antenna

Abstract

An antenna for radio frequency communication uses a magnetic current formed by a slot in a strip portion of a conductor, which may be formed as a loop to be mounted on or in a device. The length of the slot is selected to fit the available space and does not need to be a resonance length (i.e., a half or quarter wavelength of the nominal operating frequency). A terminator component may be used to terminate one end of the slot and make the slot appear from an electrical or radiative perspective to be a resonant length. The conductor may also be mounted on a detuning object or structure such as metal plate to mitigate detuning effects. A method for designing the antenna is described wherein the slot length is not restricted to being a half wavelength allowing the slot length to be selected to fit the available space.

Description

ANTENNACROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024902399 titled “Antenna” and filed on 1 August 2024, the content of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to the field of wireless radio frequency (RF) communications. In a particular form the present disclosure relates to antennas for wireless RF communications.BACKGROUND ART

[0003] In wireless communications, in particular consumer wireless communications, the antenna size is generally desired to be as small as possible, whilst still being of sufficient size to establish communications over typical links. This is particularly true in cases where the wireless communications apparatus will be located outside, and in particular, in remote outside locations, such as attached to equipment or infrastructure which are only infrequently visited. Another factor that may affect the size is the length of the communication link and the associated gain and / or directionality requirements to establish reliable communications. For example, wireless communications apparatus may need to communicate over long links, including over satellite links that are hundreds of kms long. Whip antennas offer good performance in such scenarios and are simple and relatively low -cost. However, they are prone to damage from hazards such as trees, birds, herd animals and other wildlife, marine animals and vessels, and humans.

[0004] There is thus a need to provide a small and / or compact antenna offering the advantages of a whip antenna whilst providing improved protection against damage, or to at least provide a useful alternative to existing antennas.SUMMARY

[0005] Embodiments of antennas that use a magnetic current formed by a slot in a strip of conductor will be discussed. The use of a magnetic current has the advantage that it is significantly immune (resistant) to detuning from nearby metallic objects so the antenna can exist close-to, on, or above a metal surface making it well suited for vehicle mounting or mounting on plastics or finite lossy ground -planes. Embodiments may be compact, e.g., formed as a loop, and may be designed so that the length of the slotfits the available space, whilst generating a desired radiation pattern such as a substantially omnidirectional radiation pattern, for example to enable satellite communication. That is slot length can be selected to fit a constrained mounting geometry or to fit, or retrofit, to an existing structure and the length of the slot does not need to be a resonance length, i.e., a half or quarter wavelength of the nominal operating frequency. A terminator component may be used to terminate one end of the slot and make the slot appear from an electrical or radiative perspective to be a resonant length. In some embodiments the conductor may also be mounted on a detuning object or structure such as metal plate with a known detuning effect (which can be designed for) in order to mitigate against the unknown and variable detuning effects of any surface on which the antenna may be mounted. That is the effects of the known detuning object will dominate any variable effects arising from mounting on different structures, and as they are known, they can be compensated for, or incorporated into, the antenna design (i.e., selection of slot length and dimensions).

[0006] According to a first aspect, there is provided an antenna comprising: a conductor with a strip portion; and a slot formed within the strip portion of the conductor, wherein when used, the slot generates a magnetic current and a slot length of the slot is not equal to a nominal half wavelength or a nominal quarter wavelength of a nominal operating frequency.

[0007] In some forms the slot length and a geometry of the conductor are selected to generate a predefined radiation pattern, such as a substantially omnidirectional radiation pattern. In some forms, the slot length may be selected to be less than the nominal half wavelength. For example, to maximise the length of the slot in the available space. In some forms, the conductor is a rigid conductor or is mounted on a substrate such that the strip portion of the conductor has either a loop shape or a loop like shape extending over an arc of at least 270 degrees. The loop shape or loop like shape may be a circular loop or a polygon. In some forms the slot length is within a predefined threshold amount of the half wavelength of the nominal operating frequency, and spans an arc of at least 270 degrees. For example, a mounting constraint may define a minimum arc length and a maximum arc length to achieve the desired radiation pattern, and the slot length may be selected to be the minimum or maximum arc length that is closest to the half wavelength.

[0008] In some forms the slot has a feed end and a slot end, where a feed point is located near the feed end and the slot end is an open end and a terminator component is located over the open end to make an electrical impedance of the slot electrically equivalent to a resonant length of the nominal operating frequency. This could be the nominal half wavelength, the nominal quarter wavelength, or a multiple of the nominal quarter wavelength. For example, this allows selection of a slot length with an arc length with the maximum arc length to achieve the desired radiation pattern or even anywhere between the minimum arc length and a maximum arc length to achieve the desired radiation pattern (for example to meet anotherspace / mounting constraint). If the slot length is between the nominal half wavelength and the nominal quarter wavelength then the terminator component is an inductive component. If the slot length is less than the nominal quarter wavelength then the terminator component is a capacitive component. The terminator component may be an electrical network.

[0009] In some forms, the slot has a feed end and a slot end, where a feed point is located near the feed end and the slot end is formed as a "T" shaped slot or a meander path.

[0010] In some forms, the nominal operating frequency is in an IEEE defined VHF (30 - 300 MHz), UHF (300 MHz - 1GHz ), L band (1 - 2 GHz), or S band (2-4 GHz) frequency ranges.

[0011] In some forms, the antenna further comprises a detuning object (e.g., a structure), and the conductor is mounted on, above or adjacent the detuning object. In some forms the detuning object is a metal plate. The antenna may be mounted (and the detuning object located) such that the detuning object is located between the antenna and the mounting surface or object so as to act as shield to mitigate against any detuning effects of the specific surface the antenna is mounted on.

[0012] According to a second aspect, there is provided a device containing the antenna of the first aspect, wherein the antenna is mounted on a housing of the device, or within the device.

[0013] According to a third aspect, there is provided a method of designing the antenna of the first aspect, the method comprising: receiving a set of design constraints comprising a mounting space constraint, a nominal operating frequency, and estimating a set of dimensions of at least the strip portion of the conductor using the set of design constraints such that the slot forms a magnetic current, wherein set of dimensions comprises at least a slot length, and the slot length is not restricted to being a half wavelength or a quarter wavelength of the nominal operating frequency.

[0014] In some forms, the mounting space constraint comprises that the strip portion of the conductor has either a loop shape or a loop like shape extending over an arc of at least 270 degrees. In a further form, the mounting space constraint comprises a minimum arc length and a maximum arc length, and estimating a set of dimensions comprises estimating a half wavelength of the nominal operating frequency and if the half wavelength is within a predefined amount of either the minimum arc length or the maximum arc length, then the slot length is set to the respective minimum arc length or maximum arc length. In some forms, estimating the set of dimensions may further comprises determining a terminator component to be placed over an open end of the slot to make an electrical impedance of the slot electrically equivalent to a resonant length of the nominal operating frequency. In some forms the designconstraints may further comprise a performance criteria comprising one or more of a threshold gain, a radiation pattern or a link budget, and the method further comprises assessing if the antenna meets the performance criteria. In some forms the antenna may further include a detuning object, and the conductor is mounted on, above or adjacent the detuning object, and estimating the set of dimensions may takes into account the detuning effects of the detuning object.

[0015] According to a fourth aspect, there is provided an antenna comprising: a conductor with a strip portion; and a slot formed within the strip portion of the conductor, wherein when used, the slot generates a magnetic current and the conductor is a rigid conductor or is mounted on a substrate such that the strip portion of the conductor has either a loop shape or a loop like shape extending over an arc of at least 270 degrees, and the slot extends over a predefined minimum arc length.

[0016] In some forms, the length of the slot is selected to be as close to, or equal to, a half wavelength of a nominal operating frequency whilst extending over the predefined minimum arc length or is equal to a predefined maximum arc length. In some forms a circumference of the loop or loop like shape is less than the half wavelength of the nominal operating frequency, and one or both ends are shaped with a plurality of shaping features, such as formed as a T shaped end or a meander path, such that slot length plus the path length of each of the shaping features has a total length equal to the half wavelength of the nominal operating frequency or another resonant length, or within a threshold amount of these lengths.BRIEF DESCRIPTION OF DRAWINGS

[0017] Embodiments of the present disclosure will be discussed with reference to the accompanying drawings wherein:

[0018] Figure 1A is a top view of an antenna formed from a strip of conductor with a slot according to an embodiment;

[0019] Figure IB is a side sectional view through section B-B of the antenna shown in Figure 1A according to an embodiment;

[0020] Figure 1C is a plot of the radiation pattern of the antenna shown in Figure 1A when in a planar orientation;

[0021] Figure 2A a schematic drawing of an embodiment of an antenna formed of a circular strip of a conductor with a first circumference such that an effective half-wavelength slot extends over a 90° range, and Figure 2B is a plot of the radiation pattern of the antenna shown in Figure 2A;

[0022] Figure 2C a schematic drawing of an embodiment of an antenna formed of a circular strip of a conductor with a second smaller circumference such that the effective half-wavelength slot extends over a 180° range, and Figure 2D is a plot of the radiation pattern of the antenna shown in Figure 2C;

[0023] Figure 2E a schematic drawing of an embodiment of an antenna formed of a circular strip of a conductor with a third smaller circumference such that the effective half-wavelength slot extends over an approximately 330° range, and Figure 2F is a plot of the radiation pattern of the antenna shown in Figure 2E;

[0024] Figure 3A a schematic drawing of an antenna formed of a circular strip of a conductor designed to operate at 400 MHz for communication with LEO satellites according to an embodiment and Figure 3B is a plot of the radiation pattern of the antenna shown in Figure 3A according to an embodiment;

[0025] Figure 4 is a schematic drawing of an antenna with a truncated slot and terminator component according to an embodiment;

[0026] Figures 5A and 5B are plots of the magnetic current distribution for an effective half-wave slot and a truncated slot, respectively, according to an embodiment;

[0027] Figure 6A a schematic drawing of an antenna formed of a truncated circular strip of a conductor designed to operate at 400 MHz for communication with LEO satellites according to an embodiment and Figure 6B is a plot of the radiation pattern of the antenna shown in Figure 6A according to an embodiment;

[0028] Figure 7 is a schematic drawing of an embodiment of an antenna formed of a truncated circular strip of a conductor 10 in which the lower strip extends past the slot end and reconnects to the first end of the antenna;

[0029] Figure 8A shows an embodiment in which the conductor is formed into a square (rectangular) loop and Figure 8B shows an embodiment in which the conductor is formed into an octagonal loop;

[0030] Figure 8C shows an embodiment in which the truncated slot conductor is formed into a square (rectangular) loop similar to Figure 8A and Figure 8D shows an embodiment in which the truncated slot conductor is formed into an octagonal loop similar to Figure 8B;

[0031] Figure 9 shows an embodiment in which the conductor is formed with a "T" shaped slot end;

[0032] Figure 10 shows an embodiment in which the PCB is located within the conductor loop;

[0033] Figure 11 shows an embodiment in which the antenna is mounted on a metal surface and incorporates a widened lower strip;

[0034] Figure 12A shows an embodiment in which the antenna feed line is separate and Figure 12B shows an embodiment in which the antenna feed line is integrated with the conductor 10;

[0035] Figures 13A to 13C each show an embodiment of a looped antenna 1 mounted in a cube shaped housing in three different orientations;

[0036] Figure 14 shows an embodiment in which the terminator component is a meandering track;

[0037] Figure 15 shows an embodiment of an antenna comprising two parallel slots where each slot length is designed for a different nominal operating frequency;

[0038] Figure 16 shows an embodiment of an antenna comprising two orthogonally orientated slot antennas to generate circularly polarized radiation;

[0039] Figures 17A to 17C show an embodiment of an antenna mounted in a float sensor illustrating the orientation of the float and antenna at three different water levels;

[0040] Figure 18 is a flowchart of a method for designing an antenna according to an embodiment; and

[0041] Figure 19 is a schematic diagram of a low Earth orbit satellite communications system including terminals using an antenna according to an embodiment.

[0042] In the following description, like reference characters designate like or corresponding parts throughout the figures.DETAILED DESCRIPTION

[0043] Embodiments of antennas which use a magnetic current formed by a slot in a strip portion of a conductor, as well as associated design methods, will be discussed. The radiation pattern can be controlled by selection of various dimensions of the conductor, or strip portion of the conductor, surrounding the slot and the shape (three dimensional geometry) of the conductor or strip portion of the conductor. The slot forms a magnetic current which has the advantage that it is significantly immune (resistant) to detuning from nearby metallic objects. Another advantage is that the antenna can exist close- to, on, or above a metal surface making it well suited for vehicle mounting or mounting on plastics or finite lossy ground-planes. The image of the magnetic current in a ground-plane is in the same direction as the excited magnetic current and does not contribute to destructive interference at close distances to theground-plane. As the magnetic current is confined within a strip of conductor, the fringing electric fields supporting the magnetic current do not project far from the strip, allowing metallic objects to be close to the strip. These allows the antenna to be integrated into a sensor or device housing and be located near objects such as Global Navigation System (GNS) antennas, Internet of Things (loT) modules, batteries or other sensing or communications components. In some embodiments the physical length of the slot is varied from a resonant length at the nominal operating frequency, for example made less than a half wavelength of the nominal operating frequency by using a terminator component to terminate one end of the slot. In some embodiments the slot length may be truncated from a resonant length such as a half wavelength, and thus we will generally refer to the antenna as a truncated slot antenna, but it will be understood that this term will include antennas in which the slot length is varied from a resonant length which is any multiple of a quarter wavelength. The terminator component makes the slot length appear, from an electrical or radiative perspective, to have a resonant length such as a half wavelength or some multiple of a quarter wavelength (including a one quarter wavelength). Thus, extending the slot length from a first resonance length is equivalent to a truncation of the slot length for the next quarter wavelength resonance length. The terminator component is selected to present the expected impedance to the currents which flow in the strip portion of the conductor around the slot in the case that the slot length was physically a resonant length such as a half wavelength, or another multiple of a quarter wavelength. The terminator component may be a single component, including a section of PCB artwork, or a composite component including an electrical network.

[0044] Embodiments allow the construction of compact antennas and may be designed to fit a constrained mounting geometry or be designed to be retrofitted to, including into, existing structures and devices. For example, an antenna may be designed to fit within the existing housing of a sensing device to provide (or enhance) communications capability and convert the sensing device to an Internet of Things (loT) device. This provides considerable design flexibility in contrast to traditional design approaches in which the length of the antenna is first fixed based on using a half or quarter wave antenna for a specific frequency, and then the designer has to work out how to incorporate the antenna into an existing product. These approaches lead to the use of vulnerable external antennas such as whip antennas, or additional expense as parts are reconfigured or redesigned to accommodate the fixed length of the antenna. Various embodiments will now be discussed to outline various features and design approaches.

[0045] Figure 1A shows an embodiment of an antenna 1 comprising a strip of a conductor 10 with a slot 20 in a planar (YZ) orientation. Figure IB shows a side sectional view through section B-B of Figure 1A. In the embodiment the antenna is a planar antenna lying in the YZ plane of a coordinate system with an origin located in the center of the slot 20, with the X axis extending out of the page. The ground plane is located in the XY plane, for example in a surface on which the strip of conductor 10 or substrate 40 is located. The slot separates the conductor 10 into an upper strip portion 12 with an upper width 13, a lowerstrip portion 14 with a lower width 15, and first end portion 16 and a second end portion 18. The upper width 13 and lower width 15 may be the same width, or they may be of different widths. The slot 20 has a length 21 extending from a feed end 22 to a slot end 24, and a slot width 25. The feed end 22 is adjacent to the feed point 23. The strip antenna has a strip length 11 and a strip width 17 which is the sum of the upper width 13, lower width 15 and slot width 25. In this embodiment the upper width 13 and lower width are the same dimensions. However as discussed below in other embodiments these may be different widths.

[0046] The conductor 10 may be strip of a conductor or part of a larger structure with a strip portion. The conductor 10 may be a flexible conductor such as a copper or aluminium foil, gold, silver, silver ink or fabric, or conductive polymers, or antenna could be made in a rigid form using alloys of copper, aluminium, brass, zinc plated steel, or other rigid conductors. The strip of conductor has a thickness 19 that only needs to be a fraction of a mm to support generation of the magnetic current in the slot, but may be thicker to provide additional mechanical support and rigidity to allow the conductor to be self- supporting (i.e., can be mounted and will hold a predetermined shape). In some embodiments the conductor is a self-supporting rigid structure and may include mounting points, which in some cases may be located outside of the strip portion. As shown by the dashed lines in Figure IB, in some embodiments the conductor is mounted directly onto a substrate 40 to provide structural support and define the three dimensional shape of the antenna. For example, in the case of flexible conductors such as thin foils, the substrate 40 may be used to provide structural support to the thin foil conductor and define the three dimensional shape of the antenna. In the case of semi-rigid conductors (e.g., thick foils), the substrate may act to supplement any intrinsic rigidity and maintain a desired shape, particularly against the effects of vibration or impacts / shocks during the operational life. In some embodiments the conductor 10 is sandwiched between two substrates (which may be of the same or different materials). Suitable substrates are typical PCB materials such as FR4, ceramics, or similar epoxy filled substrates, along with typical flexible substrates such as polyester, PET, polyimide, or PVC, and formable substrates such as ABS, polycarbonate, or acrylic, or indeed any other suitable radio frequency substrate. In some embodiments the substrate is the internal housing or internal component of a sensor, apparatus or loT device, or which will become an loT device once the antenna and supporting communications modules are added. In some embodiments the antenna may comprise multiple conductive layers (i.e., each layer is a conductive strip) with each pair of conductive layers separated by a substrate. In one embodiment the conductive layers may be formed as a grounded co-planar wave guide with metal on both sides of the substrate. In another embodiments the antenna may be a stripline configuration using three layers of metal conductor (each pair separated by a substrate). The use of multiple layers (and multiple substrates) may be used to provide rigidity to the antenna, and / or may provide improved strip conductivity which may the use of narrower strips of conductor on either side of the slot, i.e., upper width 13 and lower width 15 may beshorter / smaller than those used for a single layer antenna. The conductive layers may be unconnected, or conductive or ohmic vias may be used to connect the layers.

[0047] The antenna is designed to operate at one or more nominal operating frequencies. This may be a single frequency, multiple frequencies, one or more frequency bands, or a set of frequences defining or spanning one or more frequency bands (e.g., an upper and lower frequency for a frequency band). The one or more nominal operating frequencies may be one or more of a transmission frequency, a receiving frequency, a frequency located between a transmission frequency and a receiving frequency such as a central frequency, or a frequency or set of frequencies sufficiently close to one or both of a transmission frequency and a receiving frequency to enable communication. Sufficiently close will be understood by the skilled person to be a frequency that would support communication in the expected application (i.e., at a required gain or within a specific link budget) and / or at a predetermined level of service such as a target or threshold Bit Error Rate (BER) or other throughput performance metric. The antenna may be used for terrestrial communications or satellite communications, and may operate in the IEEE defined VHF (30 - 300 MHz), UHF (300 MHz - 1 GHz), L band (1 - 2 GHz) or S band (2 - 4 GHz) radio frequency (RF) ranges (and in the case of multiple frequencies, the frequencies may span multiple bands) . The choice of the nominal operating frequency (or frequencies) may be made based upon the intended communication standard or application (or applications). For example, in one embodiment the nominal operating frequency is selected to be 400 MHz to support an uplink operating at 399 MHz from a terminal to a LEO satellite, and a downlink operating at 401 MHz. LoRa and LoRaWAN operate in several frequency bands (depending upon the country) including around 433 MHz, (e.g., 433-435 MHz), 866 MHz (e.g., 863-870 MHz) and 915 MHz band (e.g., 902-928 MHz). As will be discussed below, in some embodiments the antenna may be designed to support multiple different frequencies using the same slot length, or the antenna may be designed with multiple parallel (spaced apart) slots, each slot designed for a different nominal operating frequency, or a network component may be used to switch or tune the antenna between multiple frequencies. These designs may be used in the case where the spacing of the transmit and receive frequencies is sufficiently large that a single slot cannot support communication on both links. For example, one L-band satellite communications system uses a 1.6 GHz uplink and a 1.5 GHz downlink (i.e., 100 MHz offset) and thus an antenna could be designed with a first slot optimised for communications at 1.5 GHz and the second slot optimised for communication at 1.6 GHz.

[0048] Radiation occurs due to electric currents flowing around the slot at the nominal operating frequency. This is illustrated in Figure 1C which is a plot of the radiation pattern, i.e., the gain as a function of three dimensional spatial position of the antenna shown in Figure 1 A at a nominal operating frequency of 400 MHz. At the nominal operating frequency, the radiation pattern is affected by the physical dimensions of the conductor such as slot length, slot width, upper width, lower width, feed point, the presence and composition of a substrate, as well as the three dimensional shape (or geometry) of thestrip of conductor and the slot. The slot length 21 is nominally selected to be equal to a resonance length such as the half wavelength or quarter wavelength of the nominal operating frequency in order to maximise the radiation efficiency of the antenna. It will be understood that whilst this is a common design aim, in some applications where there is sufficient link budget that maximum efficiency is not required, another slot length, such as close to a half wavelength or quarter wavelength could be chosen. In some embodiments the design of the antenna may take into account these effects to ensure the effective electrical length of the slot is a half wavelength or a quarter wavelength at the nominal operating frequency.

[0049] The feed point 23 is chosen to be close to feed end 22 to set the real part of the input impedance to a predefined value such as 50 ohms, or at least sufficiently close to the predefined value, e.g., within 10%, or with a minor imaginary component, or with a return loss (or SI 1 parameter) better than a threshold such as 10 dB. The feed point is based on the slot width, upper and lower strip widths, combined width and to a lesser degree the individual widths, the supporting substrate, and any surrounding plastics. The electric currents flowing around the slot establish an electric field between the upper strip portion 12 and lower strip 14, which follows a sinusoidal amplitude distribution in the Y direction, with a zero at the start of the slot (feed end 22) and increasing towards the right (slot end 24). If the feed point was at the start of the slot, the electric field is zero as it is shorted by the conductor at the left (first end portion 16). The impedance at this point is very low and is effectively zero ohms. As the feed point is moved to the right (towards the slot end 24), the electric field can exist, and the real part of the impedance is non -zero. There is a small inductive reactance associated with the feed point 23. Conceptually, this is equivalent to an inductor to the left of the feed point 23, but the overall slot length 21 is adjusted to absorb (resonate with) this inductance so the input impedance has only a real part (at the resonant frequency). It is only r+j'O ohms at the resonant frequency, but over a narrow bandwidth it is sufficiently close enough to the desired impedance to be acceptance, i.e., r + Jx where x is small near resonance. For example, a communication system may use an uplink at 399 MHz, and a downlink at 401 MHz (i.e., 2 MHz bandwidth), and the antenna may be designed to operate at a nominal operating frequency of 400 MHz. In this case, at 399 MHz z=50+ j’5, and at 401 MHz z=50 - j5. The feed point may be determined using simulations or experimental measurements.

[0050] As noted above radiation occurs due to electric currents flowing around the slot and thus the dimensions of the strip conductor 10, or strip portion of the conductor 10, including one or more of the upper width 13, lower width 15, first end portion 16 and second end portion 18, may be selected such that they have sufficient lengths and widths to present a low loss to these supporting electric currents. In embodiments in which the conductor is larger than the strip portion, the region of the conductor outside of the strip portion thus has a negligible effect on the radiation pattern of the antenna, and thus those regions of the conductor outside the strip portion may include mounting or anchoring points for the antenna on anobject, or also be used to support other objects. The slot width 25 may be selected based on the nominal operating frequency and the required gain for the intended application to ensure the slot is sufficiently wide to ensure radiation efficiency at the nominal operating frequency. For a predetermined nominal operating frequency simulation software may be used to determine a minimum slot width to support communication for the required application or gain, or whether a candidate slot length is sufficient to support communications. Alternatively, or additionally, the performance of a candidate slot length may be experimentally measured to test that the antenna can support communications for the required application. Typically, as the frequency is reduced, the slot width is increased in order to support the same radiation efficiency / gain (i.e., lower frequencies require larger slot widths).

[0051] In embodiments where the conductor is self-supporting and there is no supporting substrate, encapsulating plastic, mounting plastic or nearby plastic, and the feed end 22 and slot end 24 both have conductive shorts (i.e., first end portion 16 and second end portion 18 have non zero widths), then the slot length 21 may be physically set to a half or a quarter wavelength. When there is no supporting substrate and the slot length is set to a quarter wavelength, then the second end portion 18 has zero width (i.e., is not present and the slot just ends with nothing between the upper and lower strips). However, if the conductor 10 or the strip portion of the conductor 10 is on a supporting substrate 40, such as a plastic substrate, the fringing electric fields across the slot which pass through the supporting substrate, which may be on either or both sides of the conductor 10, make the effective dielectric constant within the slot higher than 1. In this case the physical slot length 21 is then made shorter than the nominal free-space half-wavelength or quarter wavelength to account for this effect. The addition of plastic thus makes the physical length shorter than the half or quarter wavelength (in the half wavelength case the length is between the shorting first and second end portions 16 and 18, and for the quarter wavelength case the length is between the shorting first end portion 16 and the second open end portion 18).

[0052] In some embodiments a supporting substrate 40 is only located on one side of the conductor 10. The electric field that exists within the slot 20 thus sees air, and thus the fringing field on the air side sees air, but the fringing field on the substrate side sees the substrate. Thus, the effective dielectric constant is not 1, and the fringing field passing through the substrate sees a dielectric constant greater than 1, so the overall or effective dielectric constant is greater than 1. Since the dielectric constant is greater than 1, the physical length 21 of the "half wavelength" slot is reduced to be less than the free-space half-wavelength so the effective "electric" length is a half wavelength (or appears electrically to be a half wavelength). In some embodiments the conductor 10 may be located (sandwiched) between two substrates. In this case the dielectric constant will be larger than the case with air on one side and a substrate on the other, and thus the physical slot length 21 may be further reduced.

[0053] In embodiments where the conductor 10 is mounted on a substrate or embedded between two substrates or located close to a plastic surface such as the housing of an loT device, no matchingcomponents are required to give a 50 ohm impedance at the feed point 23. The feed is simply a transmission line with the "ground" connected to one side of the slot 20, and the "centre" conductor traversing across the slot to make electrical contact with the other side of the slot.

[0054] The connection may be made with a piece of coaxial cable in which the braid is connected (e.g., soldered) to one side and the centre traversing across the slot is connected (e.g., soldered) to the other side of the slot. The feed-point is then arranged a distance from one of the shorted ends to set the real part of the antenna input impedance. The centre conductor connection does not necessarily need to be ohmic, and in some embodiments it could be capacitive allowing the feed to be of micro -stripline form for a one- piece antenna and feed cable solution.

[0055] If the feed line is coaxial cable, the centre conductor can traverse the slot gap and be soldered to one side of the slot. It could be soldered to a plate on the other side of the substrate, and capacitive coupling used to connect the centre conductor to the feed position. If the feed line is a micro -stripline, the centre conductor would be on the other side of the substrate to the slot conductor, so the end of the micro stripline could simply over-lap at the feed position and the over-lap region forms a capacitor to make the (non-ohmic) capacitively coupled connection. If the width of the micro -stripline is too narrow (the width is selected by the substrate thickness and dielectric constant), the end could be widened into a plate to increase the capacitance (which lowers the reactance of the connection) - a low capacitive reactance is sufficient to make the connection. Coupling in this way adds a series capacitance to the input impedance, but in a similar way to the selection of the feed position, this reactance can be tuned out by the overall slot length. Another way to terminate the micro -stripline is to continue the micro-stripline, after a 90 degree turn, for an electrical quarter wavelength ending with an open end. This open end is transformed to an effective short at the desired feed position. This technique is useful when widening the micro -stripline is not practical due to area constraints.

[0056] The spatial configuration (i.e., physical geometry) of the conductor 10 also affects the radiation pattern, as is shown in Figures 1A, 1C, and 2A to 2F. In the embodiment shown in Figure 1A, the conductor 10 is a planar conductor and the nominal operating frequency of the antenna is 400 MHz. The slot length 11 is selected to be equal to a half wavelength (375 mm) and as shown in Figure 1C, the subsequent radiation pattern produces a dipole pattern aligned along the X axis.

[0057] In the embodiment shown in Figure 1A the antenna is a planar antenna lying in the YZ plane of a coordinate system with an origin located in the center of the slot 20, with the X axis extending out of the page. In this embodiment the nominal operating frequency of the antenna is 400 MHz, and the slot length 11 is selected to be equal to a half wavelength (375 mm). Figure 1C plots the normalised electric field Eg in units of dBi and shows a radiation pattern comprised of two ellipsoidal lobes extending along the X axis away from the YZ plane containing the strip of conductor 10. Close to the origin of the coordinateaxis, Eg is around -6dBi, whereas at the distal most sections of the two lobes the Eg is around +6dBi. The distal most portion of In Figures 2A through 2F, the conductor 10 is a circular strip of progressively smaller diameters and Figures 2B, 2D and 2F illustrate the effect of the three dimensional geometry of the conductor strip on the radiation pattern.

[0058] Figure 2A is a schematic drawing of an embodiment of an antenna formed of a circular strip of a conductor with a first circumference such that an effective half-wavelength slot extends over a 90° range of the conductor strip 10. Figure 2B is a plot of the associated radiation pattern 30 of the antenna shown in Figure 2A. In this case the radiation pattern is similar to that shown in Figure 1 A, but with main axis of the lobes passing aligned with a radial vector passing through the center point of the slot (i.e., ([>=45 ° where ([>=0oat the X axis and is the angle within the XY plane; for reference, 0 is the angle with respect to the Z axis). Close to the origin of the coordinate axis, Eg is around -4dBi, whereas at the distal most sections of the two lobes the Eg is around +4dBi. Figure 2C is a schematic drawing of an embodiment of an antenna formed of a circular strip of a conductor with a second smaller circumference than that shown in Figure 2A such that the effective half-wavelength slot 20 extends over an arc with a 180° range. Figure 2D is a plot of the radiation pattern 30 of the antenna shown in Figure 2C. In this case the radiation pattern has a prolate spheroid like shape (i.e., approximately rugby ball shape) with a main axis (strongest gain) orientated along the Y axis, but with some gain extending along the X axis. This radiation pattern is less directional than the radiation pattern shown in Figures 1C and 2B but is still far from omnidirectional. Close to the Z axis, Eg is around -4dBi, whereas at the distal most sections of the two lobes along the Y axes the Eg is around +2dBi. Figure 2E a schematic drawing of an embodiment of an antenna formed of a circular strip of a conductor with a third smaller circumference (smaller than the second circumference shown in Figure 2C) such that the effective half-wavelength slot extends over an arc of approximately 330° range. Figure 2F is a plot of the radiation pattern 30 of the antenna shown in Figure 2E. In this case the radiation pattern is roughly spherical and effectively omni directional with Eg is around 2dBi over most of the lobe with a decrease / dimple around the Z axis where Eg is around -4dBi. Figures 2A to 2F thus show how as the slot is wrapped into smaller diameter tubes (or circumferences), the antenna pattern becomes more omnidirectional.

[0059] A further factor that affects the radiation pattern is slot length. As outlined above, the slot length 21 is nominally selected to be equal to the half wavelength or quarter wavelength of the nominal operating frequency in order to maximise the radiation efficiency of the antenna. In many applications it is desirable to have an omni-directional antenna pattern so that the antenna or the device on (or in) which the antenna is mounted, may be placed in any orientation and still maintain communications. If physical space permits and the radiation pattern is suitable then the slot length may be selected to be a half wavelength or a quarter wavelength. However, this requires the slot to span an arc of at least 270 degreesand preferably as close to 360 degrees allowing for the end portions 16 and 18 around the slot ends 22 and 24.

[0060] Figure 3A is a schematic drawing of an embodiment of an antenna 1 designed to operate at 400 MHz to support communication from a ground based terminal to a LEO satellite. At 400 MHz the nominal half wavelength is 375 mm which corresponds to a loop with a diameter of 120 mm. For this application a slot width 25 of 4 mm and a conductor 10 width 17 of 30 mm wide was found to be suitable to support the generation of the magnetic current. In this example the slot was located along the centreline of the conductor 10 such that the upper width 13 and lower width 15 were both 13 mm ((30-4) / 2). The first end portion 16 and second end portion 18 were also selected to have widths of 13 mm to keep the resistance in those sections similar to the resistance in the upper strip portion 12 and lower strip portion 14 giving a total circumference of the conductor strip 10 of 402 mm and a diameter of 127 mm. This embodiment generated a radiation pattern 30 as shown in Figure 3B. In this embodiment, an antenna gain of -5 dBi is required in order to close the link at the horizon from the terminal to the LEO satellites (i.e., a performance criteria of -5dBi). As shown in Figure 3B, the simulated antenna pattern has a maximum contour value of -5 dBi, representing -5 dBi gain or better. As can be seen in Figure 3B the resultant radiation pattern is substantially omni-directional. It will be understood that other dimensions may be suitable for this application. For example, simulations indicate that at 400 MHz, the upper and lower strip widths could be reduced to 10 mm whilst still maintaining acceptable performance (i.e., -5 dBi). In another variation, the antenna may be designed for both on and off metal mounting. In this application, simulations indicated an upper width 13 of 6 mm, and a lower width 15 of 14 mm, would also be acceptable with the tuning sufficiently immune to mounting on the different surfaces (i.e., -5 dBi achieved in both mounting scenarios).

[0061] The presence of nearby materials can lead to detuning effects and thus the nominal operating frequency may be adjusted to compensate for the detuning effect. In applications where the antenna may be mounted on a plastic substrate, the antenna nominal operating frequency may be slightly increased (or the slot length reduced) to compensate for the effect of the plastic mounting which will lower the frequency. Similarly, if the antenna is to be mounted on or above a metal surface, or a PCB the antenna nominal operating frequency may be slightly increased to compensate for the effect of the nearby metal which will act to lower the frequency. Detuning effects can also be minimised by making the strip of conductor that is closer to a detuning object wider. The detuning object may be located within the device containing the antenna, or a surface the device containing the antenna is mounted to. In some embodiments the antenna may be mounted on, above or adjacent a detuning object such as a metal plate or similar detuning object or detuning structure. The antenna can then be designed to compensate for the known detuning effects of the metal plate or similar detuning object and the antenna may be mounted such that the detuning object is located (and the detuning object located) between the antenna and themounting surface or object. This provides greater flexibility in mounting the antenna on a diverse range of surfaces including metal surfaces, plastics, or other materials such as bags of grain or produce. The metal plate, being closer to the antenna than the surface which the antenna is located or mounted on, contributes the largest detuning effects (which are known, i.e., they can be estimated or measured), and thus acts as a shield to mitigate against any detuning effects of the specific surface the antenna is mounted on. This allows the antenna to be designed to be largely insensitive to the material on which the antenna may be mounted. For example, Figures 6A and 7 show an antenna 1 mounted above a PCB 42, and thus equivalently the antenna could be mounted above a shield plate in the location of the PCB (i.e., replace PCB 42 with a shield plate) ,or the PCB 42 could be mounted on or above a shield plate. The detuning object could also be selected to have a larger diameter than the antenna. In some embodiments the detuning object could be a non-planar object with a known shape, for example to allow estimation of the detuning effects due to the non-planar shape. The detuning object could also be integrated with the antenna as the mounting arrangement. That is the substrate is mounted on the detuning object and the mounting object is formed with mounting points, surfaces, or structures which are used to mount the integrated antenna and the detuning object.

[0062] In many applications the available space, or circumference, in which the conductor is to be located is limited or predetermined, particularly if the antenna is to be placed within or on the housing of an existing device. In such cases using a slot length 21 equal to a half or a quarter wavelength may adversely affect the gain and / or directionality of the radiation pattern and thus reduce the communication efficiency or performance. For example, if the circumference of the housing on which a strip conductor 10 is to be mounted is significantly different to the half or quarter wavelength length, then the resultant radiation pattern may be directional such as that shown in Figures 2B or Figure 2D. In some cases, the available circumference or space may be less than a quarter wavelength. Varying the slot length from a half or a quarter wavelength leads to a reduction in the gain and communication efficiency. However, if the link budget is sufficient, and the difference between the available circumference and the half or quarter wavelength is not too large then it may be possible to vary the slot length 21 from the half or quarter wavelength so that it extends over an arc length of at least 270 degrees. This variation in slot length will result in a loss of gain or efficiency of the antenna whilst preserving omni-directionality. This may be acceptable is the loss is not too great, for example if it only drops by a threshold amount (i.e., the threshold is used as a performance criteria). The threshold may be a predetermined amount such as 1%, 5%, or 10%, or it may be a threshold gain level (-5 dBi), or it may be amount determined using an estimate of the link budget required to support communication in the expected application at a predetermined level of service. Note that the variation may be a reduction in the slot length to fit an available circumference (i.e., the half wavelength length would exceed 360 degrees) or it may be an extension of the slot length 21 (and length of the conductor 10) so that the slot length extends over an arc of at least 270 degrees (or a threshold arc angle) to preserve omni-directionality. Whether the variation isa reduction or an extension, and the amount of variation required may be determined based on the application and the specific directionality (or omni -directionality) requirements and radiation / link budget requirements (which may include quality of service requirements), so that a suitable electric length for efficient radiation can be selected.

[0063] Thus, in order to provide greater flexibility in designing the antenna, in some embodiments the slot length may be varied from the nominal physical half wavelength, and the second end portion 18 is removed and a terminator component 29 is placed across the open slot end 24. The terminator component 29 is selected to make the impedance equivalent to a resonant length such as a half or quarter wavelength and thus compensate for effects due to the variation in slot length (from the nominal length). The terminator component thus makes the slot length appear electrically equivalent to a half wavelength (i.e., a resonance length). More generally the terminator component can be selected such that the antenna has an electrical length sufficient to generate efficient radiation (i.e., gain and / or pattern) given the nominal operating frequency and application geometry. This is illustrated in Figure 4 that shows an embodiment in which the slot 20 has been truncated and a terminator component 29 has been placed across the open slot end 24. In this embodiment, the slot length 21 has been reduced so that it has a physical length less than the nominal half wavelength length but due to the terminator component 29, the slot still has an effective electrical length of a half wavelength. This approach allows the length of the slot to be varied (or adjusted) to fit an antenna into a housing that would otherwise not allow a half wavelength slot to fit, or where a quarter wave slot would fit but would lack sufficient radiation efficiency and / or radiation pattern for reliable communications. For example, in embodiments where the antenna is required to transmit to a satellite, a half wavelength may be preferred over a quarter wavelength due to the increased gain provided by the half wavelength case.

[0064] In many embodiments the available space or circumference is limited, and thus the slot length 21 will be reduced to a length less than the nominal half wavelength (i.e., the slot is a truncated slot), particularly when operating in VHF and UHF frequency ranges. In some applications a quarter wavelength may not fit within the available space, and thus the slot length could be reduced from a quarter wavelength to fit within the available space, and a terminator component 29 selected to make the slot length appear to be a quarter wavelength provided the radiation requirements are still met. Similarly, there may be applications where a quarter wavelength would fit within the available space but extending the slot length from a quarter wavelength would cover a greater arc length and improve the omnidirectionality of the radiation pattern. For example, a quarter wavelength slot may span an arc of 240 degrees in the available space (or circumference), and the slot length could be increased to span an arc length in excess of 270 degrees (and an appropriate terminator component 29 added). This could also be viewed as extending the slot from a nominal quarter wavelength or equivalently reducing (truncating) the slot length 21 from the nominal half wavelength. In some embodiments, the slot length 21 could beextended (or increased) from the nominal half wavelength and the terminator component 29 selected to make the electrical impedance of the slot 20 electrically equivalent to a resonance length such as a three quarters wavelength. More generally it is noted that an extension from an integer half wavelength can be considered a truncation of the next odd multiple of a quarter wavelength. Thus, all variations of slot length can be considered a truncation of the next resonance length. It is also noted that when extending the slot length beyond the nominal half wavelength the presence of reverse currents can affect the radiation pattern, and thus simulations or testing may be performed to ensure that the terminator component is still able to meet any gain and radiation pattern requirements of the specific application.

[0065] Referring back to the examples in Figures 1A and 4, we note that from an electrical perspective the upper strip portion 12 and lower strip portion 14 of the metal conductor on either side of the slot 20 form a parallel flat-conductor transmission line, so at any point the impedance across the slot 20 looking towards the slot end 24 is the impedance of the short circuit transformed by a length of transmission line. The impedance Zin is equal to + / Zotan ( > / ) where Zo is the characteristic impedance of the transmission line, I is length of the transmission line (slot length 21) and [3 = In / ' where A is the nominal wavelength in the transmission line. If the slot 20 is truncated so that slot length is shorter than the nominal half wavelength, the terminator component 29 placed across the open end 24 of the slot can be selected to be an inductor or an inductive load. Figures 5A and 5B show plots of the magnetic current distribution 32 for a physical half-wave slot and the truncated slot of Figure 4. As can be seen in Figure 5B, the terminator component 29 maintains the magnetic current distribution 32 of the magnetic current loop from the feed point end up 22 to the new truncated end 24. The last part of the half-sine current distribution, which would normally fall to zero at the short circuit (if second end portion 18 was present), is truncated (by the terminator component 29) up to the value that would have existed if the short was still present (i.e., no truncation). That is the addition of a shunt inductor as the terminator component 29 across the slot end 24 of the truncated slot 20 has allowed the antenna 1 to become shorter than the nominal half-wavelength (at the nominal operating frequency).

[0066] As a general comment, an odd number of quarter wavelengths requires an open ended slot, and an even number of quarter wavelengths (i.e., half wavelengths) requires a closed end slot. Thus if the removed section of the slot reduces the slot length to the nominal quarter wavelength length, then no impedance is required across the open end 24, and it is left as an open circuit (i.e., the terminator component is an open circuit) and there is no separate end portion 18 which would short the circuit (i.e., the end portion 18 is the end of the slot 24). If the slot length 21 is truncated so that it is less than the nominal quarter wavelength, the terminator component 29 would be a capacitor. While further shortening is possible, if the magnetic current loop becomes too short in overall length, then antenna gain drops, and may drop below a threshold required to maintain a communication link (which may be a threshold to meet a required quality of service). In some embodiments the slot length is increased to an odd number ofquarter wavelengths, for example three quarter wavelengths. In these embodiments the slot end 24 will be an open end and will not include a shorting end section 18 (i.e., terminator component is an open circuit).

[0067] The ability to vary or select the slot length in conjunction with the use of an appropriately selected terminator component 29 allows the antenna to be designed to fit a nominal space or the available space in an existing device. This allows the use of an omnidirectional antenna 1 into housings that would otherwise not allow a half wave slot to fit, or where a quarter wave slot would fit but lacks sufficient radiation efficiency for reliable communications. That is, an antenna can be designed to fit a nominal space, or the available space in an existing device, by selecting appropriate dimensions of the conductor including the length 21 of the slot to fit the space, and then selecting an appropriate terminator component 29 to ensure efficient radiation. We also comment that Figures 4 and 5B, and the figures that follow, illustrate truncated slot embodiments in which the slot length is varied by reducing the slot length (and using an appropriate terminator component 29). However, it is to be understood that these are illustrative only, and that as described above, the slot length could also be varied by extending beyond a half wavelength including beyond a three quarter wavelength or even beyond a full wavelength. That is the resonance length could be any multiple of quarter wavelengths (1, 2, 3, 4, 5, etc) provided a suitable radiation pattern is achieved. Also as noted above, any extension beyond a multiple of a half wavelength is equivalent to a truncation of the next multiple of a quarter wavelength.

[0068] Figure 6A is a schematic drawing of an antenna formed of a truncated circular strip of a conductor designed to operate at 400 MHz for communication with LEO satellites according to an embodiment. In this embodiment the slot length 21 has been truncated from a half wavelength of 375 mm (as shown in Figure 3A) to 274 mm which is equivalent to a reduction in the circumference from 120 mm to 87.5 mm. This embodiment can be compared with Figure 3B in which the slot length is 375 mm corresponding to a diameter of 120 mm. Figure 6B is a plot of the radiation pattern of the antenna shown in Figure 6A showing the truncated slot antenna has an omnidirectional radiation pattern with a gain of -5 dBi (or better; maximum dBi contour is -5 dBi). The gain pattern shown in Figure 6B is indistinguishable from the gain pattern shown in Figure 3B using a physical half wavelength slot demonstrating the effectiveness of truncating the slot and using a terminator component 29.

[0069] In Figure 6A the second end portion 18 is completely removed leaving a gap between the first end portion 16 and second end portion 18 of the conductor 10. Additionally, the conductor 10 is supported by a substrate 40 and is located above a PCB 42. Figure 7 is a variation of the antenna 1 shown in Figure 6A in which the lower strip portion 14 extends past the end of the slot end 24 to reconnect to first end portion 16 of the conductor 10. That is the second end portion 18 is formed only of the extension of the lower strip portion 14. This embodiment is useful to reduce stray electric fields present at the open end from interacting with the PCB 42 or other metal components which are located near to the lower stripportion 14 of the antenna, for example if the antenna was mounted on a vehicle roof. Continuing the lower strip portion 14 is also convenient for construction.

[0070] In other embodiments the shape of the antenna could be formed into a polygon. Figure 8A shows an embodiment in which the conductor is formed into a square (rectangular) loop and Figure 8B shows an embodiment in which the conductor is formed into an octagonal loop. Figures 8C and 8D show truncated slot antennas equivalent to those shown in Figures 8A and 8B. Other looped or loop like shapes may also be used. For example, the shape may form a loop if the missing end section 18 was present (i.e., truncation has created a gap in the loop). Similarly, a housing may be substantially circular, elliptical or polygonal in cross section, but have one or more portions which deviate from an otherwise regular shape, for example to accommodate another mounting, feedthrough, or component. The location of the feed end 22 and slot end 24 may be selected to minimise the effects of any deviations. Simulations or testing maybe performed to confirm the shape is acceptable for the intended application or to determine optimal mounting locations or optimal locations of the feed end 22 and slot end 24.

[0071] In some embodiments the one or both ends of the slot 20 may use a shaped end slot, such as "T" shaped end or a meander pattern such as a square wave pattern. The embodiments may be used if the desired circumference too small to allow the use of a half-wavelength slot to be formed. In this case one or both ends of the slot can be shaped for example by widening the end into a "T" shape to gain the extra electrical length required. That is the slot length, plus the path length of the two paths forming the top / cross piece of the T, has a total length equal to the half wavelength or another resonance wavelength. Figure 9 shows an embodiment of an antenna 1 in which the slot end 18 of the conductor is formed with a "T" shaped end. The "T" shaped end does affect the beam pattern, but the effect is minor. This embodiment may be selected for cases where device in which the antenna is to be mounted is just a bit too small to fit a half wavelength slot. The design is based on the observation that the magnetic current is proportional to the radiated field which is diminishing to zero as a sine wave amplitude moves to zero at the end. Thus, having a small length (i.e., the vertical bar of the T) radiating in the wrong direction does not affect the overall radiation very much. This is analogous to folding the end of an electric dipole where the electric current is small anyway. A "T" shape could be placed at both ends, but a "T" shape at the feed-point end makes finding the feed position for the desired impedance more challenging as the "good" position is typically quite close to the slot end (4 to 6 mm for 400 MHz). Similarly, one or both slot ends could be shaped with a meandering slot pattern (i.e., square wave slot pattern). Meandering of the slot is another way to electrically lengthen the slot but is more prone to etching tolerances and the meanders cause the magnetic current to flow in directions other than the main polarisation and radiation efficiency drops. Meandering may be used if there is plenty of gain in the antenna. The meandering maintains the overall beam pattern, think of a meander as "up" "right" "down" "right", the up and down cancel and the rights add so the pattern is substantially maintained but the gain or efficiency is lowered. Similarly, the"T" shaped end can be thought of as "right" ... "right" and finally "up and down" simultaneously which cancel. Other shapes can be selected such that the slot length plus the path length of the shaping features has a total length equal to the half wavelength of the nominal operating frequency or another resonant length, or within a threshold amount of these lengths.

[0072] Figure 10 shows an embodiment in which the PCB is located within the conductor loop. This is similar to the embodiment shown in 7. In this embodiment the PCB 42 containing the radio and sensor circuitry of the device is located within the antenna volume providing a compact antenna. In the above embodiments the width 13 of the upper strip portion 12 and the width 15 of the lower strip portion 14 are equal. However as shown in Figure 11, in embodiments where the antenna 1 or device containing the antenna is to be mounted to surface 44, such as on a metal surface of a vehicle or on a plastic surface, the width 15 of the lower strip portion 14 may be increased relative to the width 13 of the upper strip portion 12 to give immunity to, or at least substantially mitigate, detuning effects caused by the mounting surface. In this embodiment the lower strip portion is defined as the strip portion proximal to the surface.

[0073] The antenna is driven via a feed line 27 connected to a feed point 23 on the antenna. A separate feed line 27 may be used such as coaxial cable illustrated in Figure 12A , or the feed line 27 may be integrated into the flex-track which forms the antenna as shown in Figure 12B. Any form of connection between the antenna 1 and the PCB containing the supporting electronics may be used such as capacitively coupled, magnetically coupled or ohmic. Examples of ohmic connections are an RF connector, a solder joint either direct or via a suitable solderable connector, or in the case of a flex track feed line various push-fit connectors either interference or lockable.

[0074] The use of a looped strip antenna which generates an omni-directional radiation pattern allows mounting of the antenna in any orientation within a device including random orientation. This allows use in devices which are dropped from an aircraft or thrown into the ocean or other body of water. Figures 13A to 13C show an embodiment of a looped antenna 1 mounted in a cube shaped housing. In this case the antenna is mounted such that a central axis passing through the loop is not orthogonal to any of the planar surfaces forming the cube. That is there is a non-zero angle between the plane normal to a surface and central axis. Figure 13A shows the cube in a first orientation (Z axis vertical), Figure 13B shows the cube in a second orientation (Y axis now vertical) and Figure 13C shows the cube in a third orientation (X axis now vertical).

[0075] The antenna may be mounted to a surface or in a housing using a variety of methods including the use of formers. A flexible strip may be glued or attached with double -sided tape to a smooth surface of a plastic former or part of a plastic housing (for example the interior housing). In some embodiments the housing or former may have posts which may form thermal rivets, and the posts may also be used as mounts for fasteners. In some embodiments the strip conductor 10 may include a small notch or hole suchthat the feed cable can pass under, over, or through the strip in situations where it is convenient to have the cable on one side, but the electronics may be on the other side. In other embodiments where the strip is rigid (or semi-rigid), the former may have a bed-of-nails type mounting surface rather than a smooth surface to minimise the effect of the mounting material. The antenna could also be mounted in a ruggedised case in which the former is a metal which is appropriately spaced from the antenna, and the antenna is mounted with sparsely separated rivets, posts or fasteners, which may be insulated (where required). The conductor strip 10 may be mounted along a top edge of the strip, a bottom edge of the strip, or along both edges of the strip. The upper width 13 or lower width 15 may be increased in width (relative to the other width or the width necessary to support generation of the magnetic current in the slot) to accommodate mounting points or formations. Non-concentric formers may also be used.

[0076] In some embodiments the terminating component 29 may be a surface mount device (SMD) inductor with multiple mounting positions or a wide slide -style footprint for fine tuning, or a through hole component with multiple mounting holes may be used. These allow a common antenna to fit a range of device diameters. For a fixed device application, the inductor can be integrated into the antenna artwork in the form of a small track or wire which may coil or meander as shown in Figure 14 to yield a larger inductance. For a robust design, the antenna can be formed from sheet metal and the inductor can be implemented as a wire or strap, fastened, soldered or welded as appropriate.

[0077] In embodiments where the terminator component 29 at the open end is a capacitor, it may be a discrete component or integrated into the antenna by using overlapping plates. In truncated slot cases the terminating component 29 is an inductor if the slot has an electrical length greater than a quarter and less than a half wavelength. The inductor may be SMD, a through-hole, a track or a meander track. If the slot has an electrical length less than a quarter wavelength then the terminating component 29 is a capacitor and may be an SMD, a through-hole, or a plate integrated into the antenna conductor.

[0078] In some embodiments the antenna may be tuned for multiple frequencies. That is, it resonates at more than one frequency, such as a first frequency for an uplink and a second frequency for a downlink. In some embodiments the antenna could use a single slot, and the terminating component 29 is an electrical network that makes the one slot length electrically resonant at the two (or more generally multiple) frequencies. For example, the electrical network could look like a low -value inductor at a high frequency and a high-value inductor at a low frequency, making the antenna resonant at two frequencies. In another embodiment the electrical network could look like an inductor at a high frequency and a capacitor at a low frequency, making the antenna resonant at two frequencies. In another example the electrical network could look like a low -value capacitor at a high frequency and a high-value capacitor at a low frequency, making the antenna resonant at two frequencies. That is the electrical network is designed to look like the appropriate component at the desired frequencies. This approach may be used to make a single slot resonate at multiple frequencies and appear as a broad band antenna. The electricalnetwork may comprise a network of discrete components or one or more components with a network structure, or an artwork structure on the PCB, or some combination. In some embodiments the network may include one or more switches, tuning elements, or control elements to enable control or selection of the resonant frequency and length. This would allow external control of the resonant frequency. For example, a transceiver could switch or tune the antenna to be resonant at a transmit frequency whilst a transmission is made, then switch or tune the antenna to be resonant at a receive frequency and listen for any received signals. The networks or switches may be positioned at different regions along the slot length.

[0079] In another embodiment, the antenna 1 could be designed with multiple parallel (spaced apart) slots as illustrated in Figure 15. Each slot length 20 designed for a different nominal operating frequency and thus features a different slot length. One or both slots could be a slot with the length varied from a physical resonance length (e.g., truncated slot) and with a terminator component 29 where each component is tuned to the required electrical resonance length (e.g., half or quarter wavelength ). The spacing of the slots need only to be sufficient to allow the supporting electric currents to flow around the slot (i.e., width is sufficient to present a low loss to the other slot).

[0080] The embodiments shown with single slots generate linearly polarised radiation. However circular polarisation could be generated through the use of two orthogonally orientated slot antennas. Figure 16 shows an embodiment of first strip electrode 61 with a slot 62 formed in a loop around a first axis 63, and a second strip electrode 64 with a slot 65 formed into a loop around a second axis 66.

[0081] Embodiments allow the construction of compact antennas and may be designed to fit a constrained mounting geometry or be designed to be retrofitted to, including into, existing structures and devices. For example, an antenna may be designed to fit within the existing housing of a sensing device to provide (or enhance) communications capability and convert the sensing device to an Internet of Things (loT) device. Such an example is illustrated in Figures 17A to 17C.

[0082] Figures 17A to 17C shows an embodiment of an antenna 1 retrofitted into the housing of a conical float sensor 70 which is configured to measure the water level as part of a monitoring system. Figures 17A to 17C illustrate the orientation of the float sensor 70 and antenna 2 at three different water levels. In this embodiment the float 70 has a conical housing and includes an orientation sensor that detects or measures the orientation of the float with respect to the Z axis. The antenna was designed to fit the existing circumference of the conical housing near the top (or base) and was mounted on the interior surface of the housing. In Figure 17A the water level 72 is high, and the float sensor is floating and weighted to align with a vertical axis Z axis. As shown in Figure 17B, when the water level drops the base of the float sensor rests on the bottom of the fluid container but remains aligned with the vertical Z axis. In Figure 17C the water level has dropped to a low level, and the fluid level is insufficient to supportthe float which has tilted over and is lying on the base of the container. The orientation sensor detects when the float has tilted over and remains tilted, for example by the orientation angle with respect to the Z axis exceeding a threshold angle for a predetermined duration (threshold time period), and this triggers the float to send an alert signal via antenna 1 to an access point (e.g., LEO satellite) as part of a remote monitoring system. The antenna may also be used to send status signals to the monitoring system when the float is floating as shown in Figure 17A. Such a float device could be used to monitor the water level in a water trough or poly-tank. A similar float style device is also suitable for ocean deployment where waves change the device orientation. In both scenarios the use of a compact antenna designed to fit within the circumference of the float housing and to generate an omni-directional radiation pattern allows communication regardless of the orientation of the float.

[0083] Figure 18 shows a flowchart of a method 100 for designing an antenna. The method may be a computer implemented method. The method comprises receiving a first set of design constraints 110 including at least a mounting space constraint and at least one nominal operating frequency or wavelength. The mounting space constraint may be a circumference or a range of circumferences such as a maximum and minimum circumference, or other three dimensional data defining the available space or dimensions. Additional design constraints may include nearby materials such as the housing material (e.g., plastic), or nearby materials such a metal surface on which the device will be mounted, and environmental constraints such as expected temperature range, shock and vibration. The environmental constraints and / or nearby material constraints may be used to select the conductor, and whether the conductor will be a rigid conductor or a flexible conductor mounted on a substrate or between two substrates.

[0084] A set of dimensions of the conductor are then estimated 120 using the set of design constraints 110 such that the slot forms a magnetic current and thee set of dimensions estimated include at least the slot length. This may comprise using the nominal operating frequency or wavelength to estimate the slot length 21 without being subject to the limitation of a half or quarter wavelength of the nominal operating frequency. In some embodiments the nominal half wavelength may first be estimated (or determined) and compared with the available circumference. This may be performed in several ways. For example, a reference mounting circumference may be defined based on the available space, such as the circumference of the housing at a preferred mounting site. A minimum arc length is determined corresponding to an arc of a lower threshold angle such as 270, 300 or 330 degrees along the reference mounting circumference may then be estimated. A maximum arc angle is then determined corresponding to an arc of an upper threshold angle such as 350, 355, 356, etc degrees along the reference mounting circumference to provide a width for the second end portion 18, and the angle could be determined based on a minimum width for the second end portion 18. The determination of the minimum and maximum arc length can thus be used to define omnidirectionality requirements or take into account any limitations ofthe housing, for example, any formations, feed throughs or other components within the housing, or conductor dimensions.

[0085] If the nominal half wavelength is between the minimum arc length and maximum arc length, then the nominal half wavelength may be used as the slot length. If the nominal quarter wavelength is between the minimum arc length and maximum arc length, then the nominal quarter wavelength may be used as the slot length 21 provided it also satisfies any radiation requirements (e.g., gain) included in the set of design constraints. If the nominal half wavelength is within a predefined amount of either the minimum arc length or the maximum arc length, then the slot length is set to the respective nearby minimum arc length or maximum arc length. An assessment of the effect on the radiation pattern or link budget may also be performed to assess if this non-resonant slot length is suitable for maintaining communications in the intended application. Thus, in some embodiments the method includes an optional step 130 of assessing if the antenna meets a performance criteria comprising one or more of a threshold gain, a radiation pattern or a link budget. Otherwise, the slot length 21 is selected to be a length between the minimum arc length and the maximum arc length, and preferably close to or equal to the maximum arc length if it is desirable to maximise omnidirectionality. A terminator component 29 is also selected to make the slot length electrically equivalent to the resonance length (i.e., a multiple of a quarter wavelength). In some embodiments no check of the nominal half wavelength is performed and instead the maximum arc length is selected as the slot length 21 and an appropriate terminator component 29 determined using the maximum arc length. In some embodiments the mounting circumference, or the minimum arc length and the maximum arc length may require a slot length larger than a half wavelength or even a three quarter wavelength. If the slot length is selected to be an odd multiple of a quarter wavelength, then the selection of the terminator component comprises selecting no component and using an open slot end 24 (i.e., end portion 18 is aligned with the open slot end 24) and the terminator component is an open circuit. Simulations using antenna design and modelling software (e.g., ANSYS, MATLAB, etc) or even physical testing may be performed to estimate a slot length and terminator component to meet any gain and radiation pattern requirements (i.e., performance criteria) included in the set of design constraints. This could include performing optimisations to determine the optimum slot length and terminator component (which could be constructed as a joint optimisation process), or to assess if one or more candidate slot lengths and associated terminator components are able to meet any gain and radiation patterns included in the design constraints, particularly in cases where a candidate slot length is greater than a half wavelength. In some embodiments selection of the slot length and terminator component may include selecting a shaped end such as a “T” shaped end to obtain a resonance length. An optimisation process could also be constructed to evaluate shaped ends along with truncated slot lengths and terminator components.

[0086] Once the slot length 21 is estimated the remaining dimensions of the strip of conductor may be estimated taking into account the nearby materials. This may be the slot width 25, the width 13 of the upper strip portion 12, the width 15 of the lower strip portion 14, the width of the first end portion 16, and the width of the second end portion 18. The upper and lower widths 13 and 15 may be identical or one may be made wider to minimise any detuning due to a nearby detuning object wider. If a terminator component is used (i.e., the slot length is not an odd multiple of a quarter wavelength) the second end portion 18 may be aligned with the end of the slot 24, and a gap may be provided between the first end portion 16 and the second end portion 18 as shown in Figure 6A, or in the upper strip portion 12 or lower strip portion 14 of second end portion 18 as shown in Figure 7. A simulation or optimisation process could be performed to jointly assess or optimise slot length, terminator component and the remaining dimensions of the strip of conductor.

[0087] The above design method may be varied or extended. For example, if the antenna is designed to operate at multiple frequencies (e.g., 399 MHz and 401 MHz) and is to be mounted on a substrate or may be mounted on metals and plastics, then the nominal operating frequency may be adjusted to account for detuning effects of the substrate or nearby materials. The design process could be an iterative process or may be repeated using different parameters to create multiple designs, and then the performance of each design compared to select an optimum design based on one or more criteria (e.g., greatest gain). Simulations and experiments may be performed to assess performance or to refine an initial design.

[0088] Embodiments of antennas as described herein may be used in a wide range of communication devices, including in devices for use in a satellite communication system. Figure 19 is a schematic diagram of a low Earth orbit satellite communications system using a satellite 110 as an access node. The system 200 may be used to provide Internet of Things (loT) connectivity with remotely located sensors and assets 222 for a plurality of users 242. The satellite communications system 200 is comprised of one or more satellites 210 in a low Earth orbit (LEO) 212 which acts as an access node for a plurality of terminals 220. The terminals 220 may use embodiments of antennas 1 as described herein for communication with the access node 210. The satellite 210 communicates with a plurality of geographically distributed gateways 230, such as ground stations, which are in communication with core network infrastructure 240. The satellite 210 has a field of view 214 comprising multiple ground-based terminals 220 with communicate with the satellite 210 using radio frequency signals over a radio link 216, which may be a unidirectional downlink or a bidirectional link, and are connected to, mounted on, or in communication with sensors or assets 222. The satellite 210 communicate with a gateway 230 using radio frequency signals over a radio link 218, which may act as a downlink or uplink, e.g., to transmit commands and data to the satellite 210. The core network infrastructure 40 may include cloud -based servers which may manage the system and network routing, and provide an application interface to forward data to and from the terminals to a plurality of users 242 or otherwise provide an interface toallow users to access data provided by terminals 220. Multiple users may be supported, each communicating with different terminals 220. The gateway may send data and commands to the satellite 210 over radio link 218. The low Earth orbit satellite communications system may be a communication system as described in the following patent applications, which are incorporated by reference in their entirety:PCT / AU2013 / 000895 titled CHANNEL ALLOCATION IN A COMMUNICATION SYSTEM and fded on 14 / 08 / 2013 claiming priority from Australian Provisional Patent Application No. 2012903489 filed on 14 / 08 / 2012;PCT / AU2013 / 001078 titled COMMUNICATION SYSTEM AND METHOD and filed on 20 / 09 / 2013 claiming priority from Australian Provisional Patent Application No. 2012904130 filed on 21 / 09 / 2012;PCT / AU2013 / 001079 titled MULTI-ACCESS COMMUNICATION SYSTEM and filed on 20 / 09 / 2013 claiming priority from Australian Provisional Patent Application No. 2012904145 filed on 21 / 09 / 2012;PCT / AU2014 / 000826 titled A MULTIUSER COMMUNICATIONS SYSTEM and filed on 21 / 08 / 2014 claiming priority from Australian Provisional Patent Application No. 2013903163 filed on 21 / 08 / 2013;PCT / AU2015 / 000743 titled MULTICARRIER COMMUNICATIONS SYSTEM and filed on 9 / 12 / 2015 claiming priority from Australian Provisional Patent Application No. 2014904976 filed on 9 / 12 / 2014;PCT / AU2017 / 000058 titled TERMINAL SCHEDULING METHOD IN SATELLITE COMMUNICATION SYSTEM and filed on 24 / 02 / 2017 claiming priority from Australian Provisional Patent Application No. 2016900685 filed on 25 / 02 / 2016;PCT / AU2017 / 000108 titled POSITION ESTIMATION IN A LOW EARTH ORBITSATELLITE COMMUNICATIONS SYSTEM and filed on 16 / 05 / 2017 claiming priority from Australian Provisional Patent Application No. 2016901913 filed on 20 / 05 / 2016;PCT / AU2017 / 000286 titled SYSTEM AND METHOD FOR GENERATING EXTENDED SATELLITE EPHEMERIS DATA and filed on 21 / 12 / 2017 claiming priority from Australian Provisional Patent Application No. 2016905314 filed on 22 / 12 / 2016;PCT / AU2018 / 000151 titled SYSTEM AND METHOD FOR PREDICTION OF COMMUNICATIONS LINK QUALITY and filed on 28 / 08 / 2018 claiming priority from Australian Provisional Patent Application No. 2017903470 filed on 28 / 08 / 2017;PCT / AU2021 / 000027 titled SYSTEM AND METHOD FOR ADAPTIVECOMMUNICATIONS and filed on 29 March 2021 claiming priority from Australian Provisional Patent Application No. 2020901049 filed on 3 / 04 / 2020;PCT / AU2023 / 050178 titled COARSE GEOLOCATION OF REMOTE TERMINALS and fded on 14 March 2023 claiming priority from Australian Provisional Patent Application No. 2022900611 filed on 14 / 03 / 2022; andPCT / AU2024 / 051366 titled SATELLITE AND METHOD OF OPERATION and filed on 18 December 2024 claiming priority from Australian Provisional Patent Application No. 2023904225 filed on 22 / 12 / 2023.

[0089] Embodiments of the antennas discussed herein enable an antenna to be designed to fit the available space of a device, rather than designing an antenna to a half or quarter wavelength and then determining how to fit the antenna to the device. Embodiments use a slot in a strip of conductor and the slot and strip are dimensioned so that the slot forms a magnetic current. This approach has the advantage that it is significantly immune (resistant) to detuning from nearby metallic objects. Another advantage is that the antenna can exist close-to, on, or above a metal surface making it well suited for vehicle mounting or mounting on plastics or finite lossy ground -planes. This may include a plastic or polymer bag with virtually any contents such as but not limited to dry grain, wet grain, water, metal, vegetation, dry sand, or wet sand. The image of the magnetic current in a ground-plane is in the same direction as the excited magnetic current and does not contribute to destructive interference at close distances to the ground-plane. As the magnetic current is confined within a strip of conductor, the fringing electric fields supporting the magnetic current do not project far from the strip, allowing metallic objects to be close to the strip. These objects may be Global Navigation System (GNS) antennas, Internet of Things (loT) modules, batteries or other sensing or communications components. Embodiments allow an antenna to be designed to fit an existing space or geometry, rather than designing a half or quarter wave antenna for a specific frequency, and then having to work out how to incorporate the antenna into an existing product which can lead to the use of vulnerable external antennas, or additional expense as parts are reconfigured or redesigned to accommodate the antenna. Embodiments may be compact, e.g., formed as a loop, and may be designed so that the length of the slot fits the available space, whilst generating a desired radiation pattern such as a substantially omnidirectional radiation pattern, for example to enable satellite communication. That is slot length can be selected to fit a constrained mounting geometry or to fit, or retrofit, to an existing structure and the length of the slot does not need to be a resonance length, i.e., a half or quarter wavelength of the nominal operating frequency. A terminator component may be used to terminate one end of the slot and make the slot appear from an electrical or radiative perspective to be a resonant length. The slot ends can also be shaped, such as formed as a T-shaped or a meander path so that the slot length plus the path length of the shaping features has a total length equal to the half wavelength of the nominal operating frequency or another resonant length, or within a threshold amount of these lengths. This may be used where the available circumference is less than the half wavelength or a resonance length (and thus the slot length is less than the half wavelength). The conductor may also be mounted on a detuning object or structure such as metal plate with a known detuning effect (which can bedesigned for) in order to mitigate against the unknown and variable detuning effects of any surface on which the antenna may be mounted. That is the effects of the known detuning object will dominate any variable effects arising from mounting on different structures, and as they are known, they can be compensated for, or incorporated into, the antenna design (i.e., selection of slot length and dimensions).

[0090] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

[0091] Those of skill in the art would understand that information and signals may be represented using any of a variety of technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0092] Those of skill in the art would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software or instructions, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

[0093] The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. For a hardware implementation, processing may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, or other electronic units designed to perform the functions described herein, or a combination thereof.

[0094] In one embodiment a computing apparatus comprises at least one processor and at least one memory operatively connected to the at least one processor (or one of the processors) and may comprises additional devices or apparatus, and input and output devices / apparatus (the term apparatus and device will be used interchangeably). The memory may comprise instructions to cause the processor to execute a method described herein. The computing apparatus may be a unitary computing or programmableapparatus, or a distributed apparatus comprising several components operatively (or functionally) connected via wired or wireless connections. The computing apparatus may also comprise one or more graphical processing unit (GPUs), Tensor processing units (TPUs), input devices and output devices. A CPU may comprise an Input / Output Interface, an Arithmetic and Uogic Unit (AUU) and a Control Unit and Program Counter element which is in communication with input and output devices through the Input / Output Interface. The Input / Output Interface may comprise a network interface and / or communications module for communicating with an equivalent communications module in another device using a predefined communications protocol (e.g., Bluetooth, Zigbee, IEEE 802.15, IEEE 802.11, TCP / IP, UDP, etc.). The computing or terminal apparatus may comprise a single CPU (core) or multiple CPU’s (multiple core), or multiple processors, as well as GPUs and TPUs. The computing or terminal apparatus may use a parallel processor, a vector processor, or be a distributed computing device, including cloud based computing devices and resources. Memory is operatively coupled to the processor(s) and may comprise RAM and ROM components and may be provided within or external to the device or processor module. The memory may be used to store an operating system and additional software modules or instructions. Apparatus and devices, including sensing and display apparatus, may comprise unitary apparatus or devices or may be distributed apparatus or devices in which components are separated (for example based on function) and communicate over wired or wireless links.

[0095] Software modules, also known as computer programs, computer codes, or instructions, may contain a number a number of source code or object code segments or instructions, and may reside in any computer readable medium such as a RAM memory, flash memory, ROM memory, EPROM memory, registers, hard disk, a removable disk, a CD-ROM, a DVD-ROM, a Blu-ray disc, or any other form of computer readable medium. In some aspects the computer-readable media may comprise non-transitory computer-readable media (e.g., tangible media). In addition, for other aspects computer-readable media may comprise transitory computer- readable media (e.g., a signal). Combinations of the above should also be included within the scope of computer-readable media. In another aspect, the computer readable medium may be integral to the processor. The processor and the computer readable medium may reside in an ASIC or related device. The software codes may be stored in a memory unit and the processor may be configured to execute them. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art. A computer program may be written, for example, in a general-purpose programming language (e.g., Python, Java, C++, C, C# etc.) or some specialized application-specific language, and may utilise or call software libraries or packages for example to implement data interfaces (e.g., JSON) or utilise machine learning (e.g., TensorFlow, CUD A) or numerical optimisation.

[0096] Further, it should be appreciated that modules and / or other appropriate means for performing the methods and techniques described herein can be downloaded and / or otherwise obtained by the computingdevice. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., flash disk, RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a computing device can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.

[0097] The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and / or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and / or use of specific steps and / or actions may be modified without departing from the scope of the claims.

[0098] As used herein, the terms “estimating” or “determining” encompasses a wide variety of actions. For example, “estimating” or “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “estimating” or “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.

[0099] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g., comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0100] In some cases, a single embodiment may, for succinctness and / or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0101] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and / or features described or depicted herein.It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.

[0102] Please note that the following claims are provisional claims only and are provided as examples of possible claims and are not intended to limit the scope of what may be claimed in any future patent applications based on the present application. Integers may be added to or omitted from the example claims at a later date so as to further define or re -define the scope.

Claims

CLAIMS1. An antenna comprising: a conductor with a strip portion; and a slot formed within the strip portion of the conductor, wherein when used, the slot generates a magnetic current and a slot length of the slot is not equal to a half wavelength or a quarter wavelength of a nominal operating frequency.

2. The antenna as claimed in claim 1, wherein the slot length is less than the half wavelength of the nominal operating frequency.

3. The antenna as claimed in claim 1 or 2, wherein the conductor is a rigid conductor or is mounted on a substrate such that the strip portion of the conductor has either a loop shape or a loop like shape extending over an arc of at least 270 degrees.

4. The antenna as claimed in claim 3, wherein the loop shape or loop like shape is a circular loop or a polygon, wherein the slot length is within a predefined threshold amount of the half wavelength of the nominal operating frequency, and spans an arc of at least 270 degrees.

5. The antenna as claimed in any one of claims 1 to 4, wherein the slot has a feed end and a slot end, where a feed point is located near the feed end and the slot end is an open end and a terminator component is located over the open end to make an electrical impedance of the slot electrically equivalent to a resonant length of the nominal operating frequency.

6. The antenna as claimed in claim 5, wherein if the slot length is between the nominal half wavelength and the nominal quarter wavelength then the terminator component is an inductive component.

7. The antenna as claimed in claim 5, wherein if the slot length is less than the nominal quarter wavelength then the terminator component is a capacitive component.

8. The antenna as claimed in claim 5, wherein the terminator component is an electrical network.

9. The antenna as claimed in claim 8, wherein the electrical network is resonant at two or more nominal operating frequencies.

10. The antenna as claimed in any one of claims 1 to 4, wherein the slot has a feed end and a slot end, where a feed point is located near the feed end and the slot end is formed as a "T" shaped slot or a meander path.

11. The antenna as claimed in any one of claims 1 to 10, wherein the nominal operating frequency is in an IEEE defined VHF (30 - 300 MHz), UHF (300 MHz - 1GHz ), L band (1 - 2 GHz), or S band (2-4 GHz) frequency range.

12. The antenna as claimed in any one of claims 1 to 11, further comprising a detuning object, and the conductor is mounted on, above or adjacent the detuning object.

13. The antenna as claimed in claim 12, wherein the detuning object is a metal plate.

14. The antenna as claimed in any one of claims 1 to 13, wherein the strip portion comprises an upper strip portion with an upper width, a lower strip portion with a lower width, wherein the lower width is greater than the upper width, wherein when used, the antenna is mounted to a surface such that the lower strip portion is proximal to the surface, and the lower width is selected to mitigate detuning effects caused by the mounting surface.

15. The antenna as claimed in any one of claims 1 to 14, further comprising one or more additional slots formed in the strip portion of the conductor, each with a different slot length wherein the slot length of the respective additional slot is not equal to a half wavelength or a quarter wavelength of an additional nominal operating frequency, and the slots are spaced apart to allow electric currents to flow around each slot.

16. A device containing the antenna of any one of claims 1 to 15 wherein the antenna is mounted on a housing of the device, or within the device.

17. A method of designing an antenna of any one of claims 1 to 15, the method comprising: receiving a set of design constraints comprising a mounting space constraint, a nominal operating frequency, and estimating a set of dimensions of at least the strip portion of the conductor using the set of design constraints such that the slot forms a magnetic current, wherein the set of dimensions comprises at least a slot length, and the slot length is not restricted to being a half wavelength or a quarter wavelength of the nominal operating frequency.

18. The method as claimed in claim 17, wherein the mounting space constraint comprises that the strip portion of the conductor has either a loop shape or a loop like shape extending over an arc of at least 270 degrees.

19. The method as claimed in claim 18, wherein the mounting space constraint comprises a minimum arc length and a maximum arc length, and estimating a set of dimensions comprises estimating a half wavelength of the nominal operating frequency and if the half wavelength is within a predefined amount of either the minimum arc length or the maximum arc length, then the slot length is set to the respective minimum arc length or maximum arc length.

20. The method as claimed in claim 17, 18 or 19, wherein estimating the set of dimensions further comprises determining a terminator component to be placed over an open end of the slot to make an electrical impedance of the slot electrically equivalent to a resonant length of the nominal operating frequency.

21. The method as claimed in any one of claims 17 to 20, wherein the design constraints further comprise a performance criteria comprising one or more of a threshold gain, a radiation pattern or a link budget, and the method further comprises assessing if the antenna meets the performance criteria.

22. The method as claimed in any one of claims 17 to 21, wherein the antenna further includes a detuning object and the conductor is mounted on, above or adjacent to the detuning object, and estimating the set of dimensions takes into account a detuning effect of the detuning object.

23. An antenna comprising: a conductor with a strip portion; and a slot formed within the strip portion of the conductor, wherein when used, the slot generates a magnetic current and the conductor is a rigid conductor or is mounted on a substrate such that the strip portion of the conductor has either a loop shape or a loop like shape extending over an arc of at least 270 degrees, and the slot extends over a predefined minimum arc length.

24. The antenna as claimed in claim 23, wherein the length of the slot is selected to be as close to, or equal to, a half wavelength of a nominal operating frequency whilst extending over the predefined minimum arc length or is equal to a predefined maximum arc length.

25. The antenna as claimed in claim 23, wherein a circumference of the loop or loop like shape is less than a half wavelength of a nominal operating frequency, and one or both ends are shaped with a plurality of shaping features such that a slot length plus a path length of each of the shaping features has a total length equal to the half wavelength of the nominal operating frequency or another resonant length.

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