Broadband antenna and method for bandwidth extension of antennas

Abstract

A broadband antenna comprises an electrically conductive base body (110) and a compensation circuit (120). The electrically conductive base body (110) has at least one slot (115) along a longitudinal dimension (X) and, in a central region (M) of the slot (115) along the longitudinal dimension (X), two opposing contact areas (111, 112). The compensation circuit (120) serves to compensate for signal attenuation in received signals due to the geometry of the at least one slot (115) and to output compensated antenna signals (125). The compensation circuit (120) couples to the opposing contact areas (111, 112).

Description

[0001] The present invention relates to a broadband antenna, a vehicle with the broadband antenna and to a method for bandwidth extension of slot antennas and in particular to active, broadband slot antennas. BACKGROUND

[0002] So-called blade antennas are conventional broadband antennas. One disadvantage of these antennas is their considerable height, which is necessary to cover as wide a frequency range as possible. Therefore, it is often impossible to install these antennas in smaller aircraft or helicopters, or in or on external load containers – especially if frequencies in the HF / VHF range (30 MHz to 300 MHz) are also required.

[0003] Other conventional antennas that are not very tall include slotted antennas. These antennas are typically combined with waveguides to couple the antenna signals in and out. However, these slotted antennas are only available as narrowband antennas, for example, for radar applications. Although they are inexpensive to manufacture, they are unsuitable for many radar applications, such as signals intelligence. The frequency range they can cover is far too small.

[0004] Therefore, there is a need for broadband antennas that can cover a frequency range of at least one order of magnitude and that can be attached to land / air vehicles (airplanes, helicopters, drones, etc.) without a large installation height and therefore exhibit only low air resistance during flight. BRIEF DESCRIPTION OF THE INVENTION

[0005] At least some of the aforementioned problems are solved by a broadband antenna according to claim 1, a vehicle according to claim 12, and a method for bandwidth extension according to claim 13. The dependent claims relate to advantageous embodiments of the subject matter of the independent claims.

[0006] The present invention relates to a broadband antenna with (at least) one electrically conductive base body and a compensation circuit. The electrically conductive base body has at least one slot along a longitudinal dimension and, in a central region of the slot along this longitudinal dimension, two opposing contact areas. The compensation circuit serves to compensate for signal attenuation in received signals due to the geometry of the at least one slot and to output compensated antenna signals. The compensation circuit couples to the opposing contact areas. The compensation circuit serves for impedance matching and amplification.

[0007] The broadband antenna is therefore an active slot antenna whose bandwidth has been broadened via the compensation circuit.

[0008] Optionally, the compensation circuit includes one or more of the following components: a transimpedance amplifier for amplifying small current signals in the received signals, a low-pass filter, a balun, a signal amplifier, an analog-to-digital converter, at least one coil, at least one capacitor, a circuit board with one or more of the aforementioned components.

[0009] Optionally, at least one slot in the base body forms a slotted antenna with a frequency-dependent impedance, and the compensation circuit is designed to compensate for this frequency-dependent impedance via a (frequency-dependent) gain. It is understood that every transimpedance amplifier exhibits frequency-dependent gain. The frequency response can be adjusted by appropriately setting the parameters (e.g., selecting resistors, capacitors, etc.).

[0010] Optionally, the base body can be waveguide-free, allowing an antenna pattern to be generated on both sides of the base body. Antenna signals only need to be coupled out via the compensation circuit. Unlike conventional slot antennas, no waveguide is required for signal input and output.

[0011] Optionally, at least one slot has at least one of the following geometries: rectangular (shape of a rectangle), a constant width perpendicular to the longitudinal extent with at least one rounded end section, a constant width perpendicular to the longitudinal extent with at least one widened end section, a constant width over the entire longitudinal extent of the slot.

[0012] For example, the compensation circuit can be configured to output antenna signals in a wavelength range around a center signal, with the slot having a length of half a wavelength of the center signal along its longitudinal extent.

[0013] According to exemplary embodiments, the slot can have a length in a range between 0.15 m and 1 m and a width in a range between 0.01 m and 0.08 m.

[0014] Optionally, the at least one slot may comprise multiple slots that have the same geometry or different geometries (e.g., different lengths). The multiple slots may also be oriented differently.

[0015] Optionally, the base body can be made of a metal such as aluminum or copper.

[0016] Optionally, the base body can be formed in one piece or have several parts, with adjacent parts being separated by a slot.

[0017] Optionally, the broadband antenna also includes a casing or housing in which at least the basic body is embedded for protection (e.g., cast in or sealed airtight or watertight).

[0018] Optionally, the basic shape can form a straight line, a curved line, a square, a circle, an oval, an L, or a quadrilateral along its longitudinal dimensions. An advantage of the non-planar design lies in the adapted radiation pattern. This allows for a reduction in dead spots (so-called "blind spots") and / or the achievement of omnidirectional reception.

[0019] Optionally, the base body can have at least one of the following geometries: planar shape, curved shape, cylindrical shape with a longitudinal direction and a circumferential direction and in which at least one slot is formed along the longitudinal direction or along the circumferential direction, multi-part design such that the slot is open and is formed between two adjacent parts (of the multiple parts).

[0020] The cylindrical shape can also be triangular, square, or cuboid, as described above. An open slot is defined as one that terminates in the air and is not completely enclosed by the base body (there is no closed flow path around the slot). For example, the base body may have two or more parts or components between which the slot or slots are formed.

[0021] Optionally, in the cylindrical form, the base body has a circumference of less than 1 / 5 or 1 / 10 of a wavelength of a received signal. This can apply to both cylindrical forms, i.e., when the slot(s) are oriented longitudinally (axially) or when the slot(s) are oriented along the circumference of the cylinder.

[0022] Optionally, the basic body is an area of ​​an outer vehicle shell or vehicle superstructure.

[0023] Exemplary embodiments also refer to a vehicle with a broadband antenna, as previously described, designed to detect sources of electromagnetic radiation. According to these embodiments, multiple broadband antennas can also be present for direction finding and location tracking. The vehicle can be a land vehicle, a seacraft, or an aircraft (e.g., an airplane, a drone, or a helicopter). In the case of a land vehicle, a flat antenna could be easily integrated visually into an existing structure (e.g., roof rails, grab handles, etc.). The same applies to seacraft.

[0024] Exemplary embodiments also relate to a method for bandwidth extension of slotted antennas. The slotted antenna(s) comprise an electrically conductive base body with a slot along a longitudinal extent. The base body includes two opposing contact areas in a central region of the slot along the longitudinal extent. The method comprises: Receiving antenna signals by coupling signals from the opposite contact areas; compensating for signal attenuation due to the geometry of the slot; and outputting compensated antenna signals.

[0025] Exemplary embodiments overcome the problems of conventional antennas by using a slotted antenna formed in a blade-like body and coupled to a compensation circuit. The antenna signals are tapped (or fed) in a central region of the elongated slot, with the two contact areas (for the antenna connections) separated by the elongated slot. Therefore, this antenna does not require a waveguide for signal transmission to / from the antenna.

[0026] The compensation circuit compensates for attenuation in frequency ranges that would otherwise be unreadable by the antenna due to the slot geometry. According to exemplary embodiments, the compensation circuit includes a transimpedance amplifier, which allows the antenna to be used across a wide frequency range. For example, measurements have shown that simple slot arrangements in a metallic aluminum base allow a bandwidth of over two orders of magnitude (i.e., a factor of 100) in the frequency domain. Thus, for instance, shortwave signals in the range of approximately 10 MHz can be received with the same antenna as microwave radiation in a frequency range of 1 GHz and above. By appropriately optimizing the compensation circuit, even distant transmitters (several hundred kilometers away) can be reliably received or detected by the broadband antenna.

[0027] Another advantage of exemplary embodiments is that vertical polarization is possible with a horizontal extension (longitudinal direction). BRIEF DESCRIPTION OF THE FIGURES

[0028] The embodiments of the present invention are better understood with reference to the following detailed description and the accompanying drawings of the different embodiments, which, however, should not be understood as limiting the disclosure to the specific embodiments, but merely serve for explanation and understanding. Fig. 1A-1D shows a broadband antenna according to exemplary embodiments of the present invention. Fig. 2A-2B illustrates antenna diagrams of the broadband antenna from the Fig. 1A-1D . Fig. 3 shows a compensation circuit according to exemplary embodiments. Fig. 4 shows a schematic flowchart for a bandwidth expansion procedure. DETAILED DESCRIPTION

[0029] Fig. 1A Figure 1 shows a broadband antenna according to an exemplary embodiment from two perspectives: looking at the XY plane (top right) and at the YZ plane (to its left). The broadband antenna comprises an electrically conductive base body 110 with a slot 115 (slot-like opening). The slot-like opening 115 has a rectangular shape with a length X and a width Y, where the length X is significantly larger than the width Y (by several times, for example). The length X and / or the width Y can, for example, be constant. On the right is a top view of the XY plane (through the opening 115), and on the left is a cross-sectional view through the section plane AA'. The freely selectable thickness of the base body 110 is measured in the Z direction (perpendicular to the section).

[0030] According to exemplary embodiments, two opposing contact areas 111 and 112 are formed along the slot 115 in a central region M, electrically contacting the slot 115 on opposite sides. The slot 115 is formed between the contact areas 111 and 112 and extends on both sides of the contact areas 111 and 112 with equal lengths along the longitudinal direction X. Antenna signals can be received at the contact areas 111 and 112 and from there forwarded to a compensation circuit 120. The compensation circuit 120 is designed to amplify signal components that would otherwise be strongly attenuated due to the geometry of the slot 115. For this purpose, a frequency-dependent amplifier can be used, which amplifies the corresponding attenuated signals. Finally, the amplified antenna signals 125 are then output by the compensation circuit 120 for further processing.

[0031] In the embodiment of the Fig. 1A The base body 110 can be formed by a metal sheet or plate (blade-like) with the slot 115. A closed current path exists around the slot 115, enclosing it. Apart from the slot 115, the base body 110 is not interrupted anywhere. The base body 110 can, however, be enclosed or embedded in a dielectric shell or housing to protect it from the elements. The contact areas 111, 112 can be soldered, welded, riveted, crimped, or otherwise permanently connected to appropriate signal lines and led out of the exemplary shell or housing. The shell can also consist of a potting compound or a plastic material that does not affect the antenna characteristics but provides reliable protection against environmental influences (rain, frost, fog, dirt, etc.).The shell can also be aerodynamically shaped to be attached, for example, to the outside of aircraft (e.g. airplanes, helicopters, drones, missiles, rockets, etc.).

[0032] The Fig. 1B bis 1D show further embodiments. In the embodiment of Fig. 1B Slot 115 is open, meaning there is no closed current path around slot 115. The basic body 110 thus comprises a first part 110a and a second part 110b, separated by slot 115. It is understood that the basic body 100 can comprise any number of parts, with each adjacent part being separated by a slot.

[0033] The planar arrangement from the Fig. 1A oder Fig. 1B can be formed into cylinders according to exemplary embodiments, with the two possibilities in the Fig. 1C and in the Fig 1D are shown. The exemplary embodiment from the Fig. 1C can be obtained, for example, by the fact that in the embodiment of the Fig. 1A oder Fig. 1B the right and left sides (edges in the X direction) are connected, while the embodiment from the Fig. 1D for example, this can be obtained by the fact that in the embodiment, the Fig. 1A oder Fig. 1B The top and bottom sides (edges in the Y direction) are connected. However, the broadband antenna can have any curved shape (flat or even, cylindrical, oval, twisted, L-shaped, triangular, tetragonal, etc.).

[0034] In the cylindrical shape made of Fig. 1C or Fig. 1D The basic body 110 can have a predetermined perimeter, where the predetermined perimeter can be a value from the following: less than one wavelength of a received signal, less than 1 / 5 of one wavelength of a received signal, less than 1 / 10 of one wavelength of a received signal, less than 1 / 50 of one wavelength of a received signal.

[0035] This can be the signal from the bandwidth with the shortest wavelength (e.g., the signal with approximately 1 GHz or 300 MHz) or a center signal from the bandwidth. This can apply to both cylindrical shapes, i.e., if the slot(s) are oriented longitudinally (axially; see Fig. 1C ) and / or if the slot(s) are formed along the circumference of the cylinder (see Fig. 1D The limitation of the circumference has the technical effect that circulating currents around the cylinder, which can occur with cylindrical geometry, have no negative effect on reception, do not interfere, or are not dampened by the geometry.

[0036] In further embodiments, a rectangular or triangular shape is used instead of a cylindrical one. Here too, one or more slots can extend along the longitudinal shape or, perpendicular to it, in the circumferential direction.

[0037] The cylindrical body 110 can also have several parts, each with a slot 115 between them. That is, the ends in the longitudinal axis of the cylinder or in the circumferential direction can also be open (as in Fig. 1B shown).

[0038] According to the examples given, the casing can also be used as camouflage (for military applications). Optionally, the casing can be adapted to or integrated into the vehicle's visual structure (e.g., into a railing or an existing grab handle). It is then not perceived as a separate component. The broadband antenna or its base can be part of an outer vehicle shell (part of the vehicle body) or a vehicle superstructure. It is advantageous if the slot is sealed or covered with dielectric material. After painting, the broadband antenna can thus be completely invisible.

[0039] The cross-sectional view (left in the Fig. 1A Figure 1 shows that the base body 110 can be formed symmetrically on both sides of the slot 115. Therefore, the antenna can receive the antenna signal on both sides in the Z direction. The broadband antenna can thus look the same on the front and back.

[0040] All limitations that apply to the exemplary embodiment from the Fig. 1A The described features can also be found in the other embodiments (e.g., from the Fig. 1B bis 1D ) be implemented.

[0041] Fig. 2A und Fig. 2B Show simulation measurement results for antenna diagrams 210, 220, 230, 240 of the broadband antenna as a function of frequency, where the Fig. 2A which represents the XY plane (360° azimuth) and the Fig. 2B The YZ plane is represented (180° elevation). The example aircraft 50 is intended to indicate the location of the broadband antenna. It is understood that if mounted on aircraft 50, the aircraft 50 itself will interfere with the antenna pattern – depending on where the antenna is installed (e.g., on the underside of the fuselage, the top of the fuselage, under a wing, etc.).

[0042] This influence will be disregarded here. Instead, the antenna diagrams are intended to show that the broadband antenna can receive signals symmetrically from both the Y and Z directions. Furthermore, antenna diagrams 210, 220, 230, and 240 illustrate the achievable bandwidth: the first antenna diagram (210) refers to a first frequency of approximately 50 MHz, the second antenna diagram (220) to a second frequency of approximately 250 MHz, the third antenna diagram (230) to a third frequency of 500 MHz, and the fourth antenna diagram (250) to a fourth frequency of approximately 1,000 MHz. The broadband antenna can therefore cover a frequency range from at least 50 MHz to 1,000 MHz without experiencing a significant loss of signal strength. At the highest frequency of 1 GHz, only side lobes appear in and against the direction of flight. However, the lateral signal strength is at its maximum for the highest frequency.Such a bandwidth of 1:20 (from the lowest to the highest frequency) without any significant signal loss is not achievable with conventional slot antennas.

[0043] This bandwidth extension was achieved by coupling the compensation circuit 120, which is described in more detail below.

[0044] According to the exemplary embodiments, the radiation pattern is omnidirectional, radiating into the free-space environment. For example, the broadband antenna with the cylindrical shape can be made from the Fig. 1C The signal is received in the entire circular plane (perpendicular to the cylinder's longitudinal axis) in a 360° arc. This variant is suitable for lateral mounting on a metallic body. In this case, the radiation pattern becomes one-sided and the impedance changes. This is very advantageous for aircraft applications, as it eliminates the need for under-aircraft installations, allowing for lateral mounting.

[0045] Fig. 3 Figure 1 shows an example of a compensation circuit 120, as it can be used according to the exemplary embodiments. The compensation circuit 120 couples to the two contact areas 111, 112 on the slot 115 of the broadband antenna. The compensation circuit includes, by way of example, a transimpedance amplifier 122, a signal amplifier 126, a balun 124, a low-pass filter 123, and an optional analog-to-digital (A / D) converter 127. The transimpedance amplifier 122 and the signal amplifier 126 can also be implemented by a single component that is frequency-selective, for example, to amplify attenuated signals. The transimpedance amplifier used for this purpose amplifies (weak) current signals into amplified voltage signals, which can then be processed more effectively.

[0046] The Balun 124 (balanced-unbalanced) is a component that converts an unbalanced input signal (with one ground contact) into a balanced output signal (the electrical potential at both contacts changes). It typically comprises two coils coupled together, with the ground connection potentially being a center contact. Because of the Balun 124 circuit, a standard coaxial cable (e.g., at the input) can be used for the unbalanced signal.

[0047] The optional low-pass filter 123 is designed to allow low-frequency signals to pass through while filtering out or suppressing high-frequency signals. This is intended to separate the desired signal from high-frequency noise. The optional A / D converter 127 can then be used, for example, to convert the analog input signals into digital signals 125, which can then be evaluated in a subsequent signal processing circuit.

[0048] The order of the individual components in the compensation circuit 120 can also be chosen differently. For example, the balun 124 can also be implemented directly at the input or at the output of the compensation circuit 120. Likewise, several amplifiers can be provided (e.g., also after the low-pass filter 123). Similarly, several low-pass filters 123 can be present to successively filter out increasing amounts of noise.

[0049] This compensation circuit 120 makes the broadband antenna an active slotted antenna, where the active components (such as the exemplary transimpedance amplifier) ​​are used to adjust the bandwidth extension according to the wishes and requirements.

[0050] It goes without saying that it doesn't necessarily have to be a transimpedance amplifier. Any amplifier with a low input impedance can be used.

[0051] Fig. 4 Figure 1 shows a schematic flowchart for a method for bandwidth extension of slot antennas. The slot antenna comprises – as previously described – an electrically conductive base body 110 with a slot 115 along a longitudinal extent X, wherein the base body 110 has two opposing contact areas 111, 112 in a central region M of the slot 115 along the longitudinal extent X. The method comprises: Receiving S110 of antenna signals by coupling signals at the opposite contact areas 111, 112; compensating S120 of signal attenuation due to a geometry of the slot 115; and outputting S130 of compensated antenna signals 125.

[0052] The base body 110 can be made of materials such as aluminum or copper, although embodiments are not necessarily limited to a specific material. Other metallic materials can also be used, into which corresponding slots 115 can likewise be formed.

[0053] According to exemplary embodiments, the slot 115 can be adapted to the requirements of the respective antenna. For example, the slot 115 can have a length X of 30 cm or more or less. The width Y can be selected in a range between 0.5 cm and 2 cm. It is understood, however, that the slot geometry can be selected almost arbitrarily and adapted to the desired broadband frequency range. In contrast to conventional slot antennas, the slot length X does not need to be half the wavelength to be received. According to exemplary embodiments, this can be significantly different (by a multiple). Exemplary embodiments allow the reception of longer or shorter wavelengths than those that would correspond to twice the slot length X.

[0054] Examples of this design can be used in particular for linear interferometers or circular group antennas and are very well suited for locating transmitters and determining their position.

[0055] Another advantage of the broadband antenna according to the exemplary embodiments is that it does not require a waveguide for coupling in / out signals. The base body 110 itself also has no interior. The broadband antenna can simply be formed as a metal plate (base body 110) with the slot 115, which can be contacted via the contact areas 111, 112 and the compensation circuit 120. Thus, signals can be received equally on both sides of the base body 110 or the slot 115. The height along the Y-direction of the base body 110 can be limited to a few centimeters and is essentially only restricted by the slot width Y. Since the slot width Y can be chosen to be very small (e.g., less than 1 cm or a few centimeters), the overall height when attached to an aircraft 50 can be very low.This offers the significant advantage that, when used in aircraft, the broadband antenna presents no noticeable air resistance and can be mounted at any point on the aircraft. For example, due to its low profile, the broadband antenna can be mounted on the underside of the aircraft, eliminating the risk of ground contact.

[0056] Due to its compact design, the broadband antenna can be mounted on the aircraft in almost any configuration. For example, the slot 115 can extend in the direction of flight, and the Z-direction can extend horizontally on both sides of the aircraft (see cross-section AA' in [reference]). Fig. 1 This results in the symmetrical antenna pattern being derived from the Fig. 2A and the Fig. 2Bachieved. According to further embodiments, several slots 115 can also be formed in the base body 110, or several antennas can be combined to enable the greatest possible coverage in a lower area as well as in the two side areas of the aircraft.

[0057] Compared to conventional "blade" antennas, which can also be made compact, these embodiments offer the advantage that vertical polarizations are possible with a horizontal slit or oriented. This is not possible with conventional "blade" antennas.

[0058] In summary, exemplary embodiments define a novel antenna design particularly well-suited for broadband applications, allowing bandwidth extension factors between the band limits of 1:20 or 1:100 or more. Therefore, the antenna is especially well-suited for military radar and communication signal reconnaissance. Further advantages include the inherent grounding of the radiator to the aircraft structure, as the base body 110 can be directly connected to metallic parts of the aircraft structure, ensuring a reliable ground connection. This also results in high resistance to electrostatic discharge, lightning strikes, and bird strikes.

[0059] The features of the invention disclosed in the description, claims and figures may be essential for the realization of the invention, either individually or in any combination. REFERENCE MARK LIST

[0060] 50 Aircraft (e.g., airplane, drone, helicopter, rage) 110 Base body 115 Slot, opening 111, 112 Contact areas 120 Compensation circuit 122 Transimpedance amplifier 123 Low-pass filter 127 A / D converter 124 Balun 125 Antenna signals 126 Signal amplifier 210, 220, 230, 240 Antenna diagram at various frequencies M Center area in slot XL Length, longitudinal direction Y Width, transverse direction Z Depth, thickness

Claims

1. Broadband antenna comprising: an electrically conductive base body (110) with at least one slot (115) along a longitudinal extent (X), wherein the base body (110) has two opposing contact areas (111, 112) in a central region (M) of the at least one slot (115) along the longitudinal extent (X); and a compensation circuit (120) for compensating signal attenuation in received signals due to a geometry of the at least one slot (115) and for outputting compensated antenna signals (125), wherein the compensation circuit (120) couples to the opposing contact areas (111, 112).

2. Broadband antenna according to claim 1, wherein the compensation circuit (120) comprises at least one of the following components: - a transimpedance amplifier (122) for amplifying small current signals in the received signals, - a low-pass filter (123), - a balun (124), - a signal amplifier (126), - an analog-to-digital converter (127), - at least one inductor, - at least one capacitor, - a printed circuit board with one or more of the aforementioned components.

3. Broadband antenna according to claim 1 or claim 2, wherein the at least one slot (115) in the base body (110) forms a slot antenna with frequency-dependent attenuation, and the compensation circuit (120) is designed to compensate the frequency-dependent attenuation via a frequency-dependent gain.

4. Broadband antenna according to one of the preceding claims, wherein the base body (110) is waveguide-free, so that an antenna pattern (210, 220, 230, 240) can be generated on both sides of the base body (110) and the coupling of antenna signals (125) takes place only via the compensation circuit (120).

5. Broadband antenna according to one of the preceding claims, wherein the at least one slot (115) has at least one of the following geometries: - rectangular, - a constant width (Y) perpendicular to the longitudinal extent (X) with at least one rounded end section, - a constant width (Y) perpendicular to the longitudinal extent (X) with at least one widened end section, - a constant width (Y) over the entire longitudinal extent (X) of the slot (115).

6. Broadband antenna according to claim 5, wherein the at least one slot (115) has several slots having the same geometry or different geometries.

7. Broadband antenna according to one of the preceding claims, wherein the base body (110) is made of metal such as aluminium or copper.

8. Broadband antenna according to one of the preceding claims, further comprising a casing in which at least the base body (110) is protected and embedded.

9. Broadband antenna according to one of the preceding claims, wherein the base body (110) has at least one of the following geometries: - planar shape, - curved shape, - a cylindrical shape with a longitudinal direction and a circumferential direction and in which at least one slot (115) is formed along the longitudinal direction or along the circumferential direction, - a multi-part design, such that the at least one slot (115) is open and is arranged between two adjacent parts.

10. Broadband antenna according to any one of claims 1 to 9, wherein the base body (110) in the cylindrical form has a circumference of less than 1 / 5 or 1 / 10 of a wavelength of a received signal.

11. Broadband antenna according to any one of claims 1 to 10, wherein the base body (110) is a region of an outer vehicle shell or vehicle body.

12. Vehicle with: a broadband antenna according to one of the preceding claims for detecting sources of electromagnetic radiation.

13. Method for bandwidth extension of slot antennas, wherein the slot antenna has an electrically conductive base body (110) with a slot (115) along a longitudinal extent (X) and the base body (110) has two opposing contact areas (111, 112) in a central region (M) of the slot (115) along the longitudinal extent (X), the method comprising: receiving (S110) antenna signals by coupling signals at the opposing contact areas (111, 112); compensating (S120) signal attenuation due to a geometry of the slot (115); and outputting (S130) compensated antenna signals (125).

Images