Substrate-integrated-waveguide system

Abstract

A substrate-integrated-waveguide, SIW, antenna or radio frequency, RF, filter system, the SIW system. The SIW system comprises a first SIW comprising a first substrate having first dielectric constant and / or a first thickness; and a second SIW coupled to the first SIW substantially at a centre of the first SIW such that the first SIW is a centre-fed SIW and comprising a second substrate having a second dielectric constant which is greater than the first dielectric constant and / or a second thickness which is greater than the first thickness.

Description

[0001] SUBSTRATE-INTEGRATED-WAVEGUIDE SYSTEM

[0002] Technical Field

[0003] The present invention relates to a Substrate-Integrated-Waveguide (SIW) system, such as an antenna.

[0004] Background

[0005] SIWs are waveguide structures typically used in high-frequency applications, such as RF systems in the microwave and millimetre-wave frequency ranges. An SIW comprises a dielectric substrate with conductive elements defining a waveguide structure within the substrate. The conductive elements may include a bottom ground plane and a top ground plane, with conductive elements extending between the top and bottom ground plane.

[0006] The dielectric substrate generally contains the electromagnetic waves, while the conductive elements act as walls of the waveguide, preventing the radiation of electromagnetic energy outside the structure.

[0007] SIWs may be used in various RF systems and devices, where a transmission line is required, including antennas and RF filters.

[0008] An SIW slot array is a type of antenna based on the SIW technology. A series of slots or openings are patterned through one of the ground planes. Each slot acts as an aperture through which electromagnetic waves can propagate, effectively coupling energy into or out of the SIW structure. SIW slot array antennas offer efficient operation at millimetre-wave (mm-wave) frequencies.

[0009] SIW slot array antennas offer advantages such as a wider beamwidth and a more controlled radiation pattern. However, it is difficult to connect SIW slot array antennas with other kinds of transmission lines.

[0010] Typically, the SIW will be fed at one end. However, as the wavelength changes over a broad frequency range, a progressive phase shift occurs along the array causing antenna squint which may be undesirable.

[0011] To limit the antenna squint, as well as providing a natural amplitude weighting across the array aperture, it has been proposed to feed the SIW slot array antenna in the centre. However, this approach generally does not offer a wideband impedance match from the feed point. Other RF devices, such as filters, may also require a centre coupling between SIWs and would benefit from an improved impedance match.

[0012] Summary

[0013] Techniques described herein relate to improving the performance of a centre- fed SIW, for example as might be used in RF devices such as an RF filter or a slot array antenna. The inventors have found that an improved broadband impedance match is provided between a feed SIW and a destination SIW, such as an antenna SIW, comprises a substrate with a lower dielectric constant than a substrate of the feed SIW. An improved broadband impedance match is also provided when the feed SIW is thicker than the destination SIW. Moreover, these two features can be combined to further improve a broadband impedance match.

[0014] According to a first aspect of the present invention, there is a substrate- integrated-waveguide, SIW, system. The system comprises a first SIW comprising a first substrate having first dielectric constant; and a second SIW coupled to the first SIW substantially at a centre of the first SIW and comprising a second substrate having a second dielectric constant which is greater than the first dielectric constant.

[0015] The difficulty in connecting SIWs to various other transmission lines extends to the coupling of an SIW to another SIW such as the coupling between the first and second SIW in the antenna of the first aspect. This difficulty is at least partially addressed by the antenna of the first aspect. Specifically, the inventor has found that the difference in the first and second dielectric constants allows for an efficient, broadband, centre-fed SIW transition. In particular, it has been found that the difference between the first and second dielectric constants broadens the bandwidth over which a characteristic impedance is maintained from the second SIW to the first SIW. This improves the bandwidth over which an acceptable impedance match is achieved, reducing signal reflections at an interface between the first and second SIWs. The result is improved antenna performance over a broad range of frequencies.

[0016] This is a somewhat surprising result, as even if it were considered that using substrates having different dielectric constants may have an impact on impedance bandwidth, traditional belief would lead to the idea that the first dielectric constant should be the same as the second dielectric constant. However, it has been found that this is not the case and improved performance arises from the first dielectric constant being less than the second dielectric constant.

[0017] According to transmission line theory, reducing the dielectric constant in the first SIW actually increases a waveguide characteristic impedance. However, the centre-fed nature of the first SIW means that the transition essentially acts as a tee- junction. The impedance seen at a feed input of the first SIW is lower than the characteristic impedance of a single transmission line. Therefore, the combined characteristic impedance of the first SIW remains constant with respect to the second SIW over a wider range of frequencies.

[0018] The substrate may be formed from a single PCB core from two or more PCB cores in a laminated multilayer PCB structure.

[0019] The coupling between the first and second SIWs allows electromagnetic radiation to be transmitted from the second SIW to the first SIW. For this reason, the second SIW may be referred to as a feed SIW, since it is arranged to feed the first SIW with the electromagnetic radiation. In some examples, the first and second SIWs are arranged such that the second SIW feeds the first SIW from behind, or under, the first SIW.

[0020] The second SIW may be arranged to receive an electromagnetic radiation signal from a source. The signal is guided by the second SIW waveguide structure to the region of coupling between the first and second SIWs, which may be referred to as a transition structure. The first SIW’s structure is configured to couple the signal to a radiating structure on a surface of the first SIW such that at least a portion of the signal is radiated externally from the antenna. The first SIW may be referred to as a centre-fed SIW because of the substantially central coupling between the first and second SIW.

[0021] The reference to “substantially at a centre” of the first SIW is used to refer to a “Tee” type connection between the first and second SIW. The centre may be a centre of a longest dimension of the first SIW, such as a centre along a length of the SIW.

[0022] In some examples, the first dielectric constant is between 10% to 40% less, 15 to 30% less, or 16% to 27% less than the second dielectric constant. This difference in dielectric constants has been shown to result in good characteristic impedance matching behaviour across the transition. In some examples, the first dielectric constant may be less than or equal to 3, in other examples the first dielectric constant may be less than 3.

[0023] In one example, the first dielectric constant may be around 2.2. A second dielectric constant around 3 and a first dielectric constant around 2.2 have been shown to provide good performance.

[0024] Materials having dielectric constants below 3 may be more expensive than those with dielectric constants 3 or above. With this in mind, the first dielectric constant may be around 3 and the second dielectric constant may be higher, for example around 3.6. This may also provide improved broadband impedance matching while being reducing component costs.

[0025] SIW systems according to this disclosure may have a return loss for signals travelling from the second SIW to the first SIW of at least 10 dB across a percentage bandwidth of at least 10% about a centre frequency. The percentage bandwidth is defined as the ratio of the absolute bandwidth to the centre frequency, expressed as a percentage. In some cases, the return loss of at least 10 dB may be across a percentage bandwidth of at least 15%, at least 20%, or at least 25%. The centre frequency may be above around 8 GHz, such as from around 8 GHz to around 100 GHz. Such large relative bandwidths are difficult to achieve at centre frequencies above 8 GHz.

[0026] Alternatively, or additionally, SIW systems according to this disclosure may have a return loss for signals travelling from the second SIW to the first SIW of at least 10 dB across a bandwidth of at least 10 GHz, or at least 20 GHz. Such a low return loss across these bandwidths has not previously been possible for centre-fed SIW antennas. In an example, the operating frequency range over which this return loss is achieved may be between 55-75 GHz, while in another example the frequency range may be 70- 90 GHz. More generally, the 25% bandwidth may be in the range of X-band (around 8 GHz) to W-band (around 100 GHz). Return loss can be determined in any suitable manner, for example by injecting a signal of known rms amplitude and measuring the rms amplitude of the reflected signal, or by simulating the design in software such as SEMCAD X Matterhorn commercially available from Schmid and Partner Engineering AG, or CST Studio Suite(RTM) commercially available from Dassault Systemes.

[0027] A transition between the first and second SIWs may comprise a blind via and an internal slot, each positioned substantially at the centre of the first SIW. This arrangement defines a T-section split between the second SIW and the first SIW. The blind via may be arranged to prevent a signal travelling past the internal slot, such as by filling it with conductive material, while the slot may be arranged, designed, or configured to provide the means to couple the first and second SIWs. Dimensions of the slot may be determined based on known optimisation techniques such as those provided in simulation software. Some examples have a generally rectangular slot with a ratio of longest to shortest dimension of between 4 and 7, or between 5 and 6. In one example the slot has a longest dimension of around 1.6 mm and a shortest dimension of around 0.3 mm.

[0028] The first substrate may have a thickness which is less than a thickness of the second substrate. This has been shown to provide further improvements in broadband impedance matching. Thickness is the dimension perpendicular to the plane of the substrate. In some examples, the first substrate may be 70% to 80% of the thickness of the second substrate, such as around 75% of the thickness of the second substrate. Put another way, a minimum dimension of the second SIW may be larger than a minimum dimension of the first SIW. The first and second SIW may have substantially planar geometries (e.g. rectangular parallelepipeds) wherein the minimum dimension (e.g. thickness) of the second SIW is greater than that of the first SIW.

[0029] The second SIW (also referred to as the feed SIW) may be coupled to a source in any suitable way. In one example, a grounded-coplanar-waveguide (GCPW) may be provided as a source of the electromagnetic radiation signal and may be coupled to the second SIW via the techniques described in “Practical Low-Loss Substrate-Integrated- Waveguide Feed Network for mm-Wave PCB Antenna Designs,” 2020 14th European Conference on Antennas and Propagation (EuCAP), Copenhagen, Denmark, 2020, pp. 1-5, J. R. Henderson and M. C. Walden. Coupling to a GCPW may provide a simple- to-manufacture, yet efficient, feed network for a low-loss SIW.

[0030] The antenna may be implemented in a multi-layer printed circuit board (PCB), comprising at least three layers. In some examples, the antenna may be implemented in a PCB comprising at least six layers.

[0031] The antenna may comprise a plurality of through-hole vias are arranged to confine the signal within the first SIW and / or the second SIW. For example, the plurality of through-hole vias may be filled with a conductive material. The SIW system may form part of an antenna, wherein the first SIW is configured to radiate electromagnetic radiation via a plurality of radiating slots. For example, these slots may be formed in an outer conductive layer of the first SIW. The slots may be providing an any suitable arrangement and may form a slot array.

[0032] The first SIW may be configured to radiate electromagnetic radiation in any suitable way, such as by providing one or more slots through which electromagnetic waves can transition out of the first SIW. In some examples, the first SIW may be an SIW slot array antenna. A slot array antenna may comprise a series of slots, apertures, or openings patterned on the surface of the first substrate. Each slot acts as an aperture through which electromagnetic waves propagate, effectively coupling energy into or out of the first SIW. The slots may be arranged in a regular pattern, such as a linear array or a two-dimensional array. The dimensions and spacing of the slots are chosen to achieve desired antenna characteristics, such as radiation pattern polarization. The dimensions and arrangement of the slots may be determined, or designed, to tailor the performance of the SIW slot array to meet specific requirements. This includes optimising characteristics such as antenna gain, bandwidth, efficiency, and radiation pattern. The optimisation may be performed using known techniques including through the use of simulation software such as SEMCAD X Matterhorn or CST Studio Suite(RTM).

[0033] According to a second aspect of the present invention, there is provided a centre- fed substrate-integrated-waveguide, SIW, antenna, comprising: an antenna SIW configured to radiate electromagnetic radiation; and a feed SIW coupled to the antenna SIW. The antenna SIW comprises a substrate having a dielectric constant which is lower than a substrate of the feed SIW. The SIW antenna of the second aspect may share any of the properties with the antenna of the first aspect.

[0034] According to a third aspect of the present invention, there is provided a substrate-integrated-waveguide, SIW, system. The system comprises a first substrate having a first thickness; and a second SIW coupled to the first SIW substantially at a centre of the first SIW and comprising a second substrate having a second thickness which is greater than the first thickness.

[0035] It has also been shown that a change in substrate thickness across the transition has a significant improvement on the transition bandwidth, independently of the difference in dielectric constants between the first and second substrates. The system of the third aspect may also include one or more of the features as discussed above for the first aspect.

[0036] According to a fourth aspect of the present invention, there is provided a system comprising a first SIW system and a second SIW system. The first and second SIW systems may be defined according to any of the first, second or third aspects. The first SIW system is positioned adjacent to the second SIW system. Adjacent in this context means that the SIW systems are positioned next to each other, for example in a side- by-side arrangement within the same plane. In some examples, the first and second SIW systems are directly adjacent each other, such as directly adjacent within the same plane. The first and second SIW systems may be arranged such that a longest dimension of the first SIW system is positioned parallel to a longest dimension of the second SIW system.

[0037] The system may comprise additional SIW systems, for example, forming an array such as a linear array, a two-dimensional rectangular array, a circular array, or other suitable configurations depending on the desired electromagnetic radiation pattern and application requirements.

[0038] Two or more SIW systems can work together to provide enhanced electromagnetic performance compared to a single SIW system. For example, by arranging multiple SIW systems in an array configuration, the system can achieve improved gain, directivity, and bandwidth characteristics, when implemented as an antenna system.

[0039] A spacing between the first and second SIWs may be referred to as an SIW pitch. The SIW pitch may be determined based on a predetermined wavelength of electromagnetic radiation that the system is configured to operate with. In some examples, the first and second SIW systems may be spaced at an SIW pitch of substantially half the predetermined wavelength. Spacing adjacent SIW systems on a half-wavelength pitch avoids the onset of grating lobes, which are undesired radiation lobes that form at angles other than a main beam direction. Placing a feed structure behind the first SIW of each SIW system allows the first and second SIW systems to be positioned contiguously. This is in contrast to conventional systems wherein an array element is fed from the side, parallel to the planar array. In this case, this increases the width of the array element and feed structure such that the next array element cannot be placed within half a wavelength.

[0040] The first SIW system may comprise a plurality of through-hole vias that are arranged to confine a signal within at least one of the first SIW and the second SIW. The second SIW system may share the plurality of through-hole vias with the first SIW system. The plurality of through-hole vias may be referred to as a via wall. Sharing a common via wall allows the SIW pitch required for operation at a given wavelength to be maintained, thereby avoiding the onset of grating lobes while preserving the electromagnetic isolation required for proper waveguide operation.

[0041] According to a fifth aspect of the present invention, there is provided a transceiver including an antenna comprising an SIW system or system according to any of the above-described aspects when applied to an antenna.

[0042] According to a sixth aspect of the present invention, there is provided a radar system comprising the transceiver of the fifth aspect.

[0043] According to a seventh aspect of the present invention, there is provided a radio frequency system comprising the SIW system or system of the first, second third, or fourth aspect.

[0044] Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

[0045] Brief Description of the Drawings

[0046] Figure 1 shows an external view of antenna according to an example;

[0047] Figure 2 shows an internal view of a radiating antenna according to an example;

[0048] Figure 3 shows an alternative internal view of the radiating antenna shown in Figure 2;

[0049] Figure 4 shows an example PCB stack in which an SIW antenna may be implemented;

[0050] Figure 5A shows an electric field distribution around an antenna according to an example;

[0051] Figure 5B shows a cross sectional view of the electric field distribution around the antenna shown in Figure 5A; and Figure 6 shows a plot of return loss across a range of frequencies showing the benefits of an embodiment of an SIW system.

[0052] Detailed Description

[0053] As has described above, SIWs are difficult to connect with or transition to other kinds of transmission lines, including other SIWs. An inefficient transition results in a large amount of reflection of a signal back towards a source. It is desirable to make a transition more efficient across a broad range of signal frequencies. This is equivalent to improving the impedance match at the transition across a broad range of frequencies. The present disclosure relates in general to improving the transition between a first SIW and a second SIW and is particularly applied to centre-fed SIW antennas.

[0054] Figure 1 shows a diagrammatic external view of an antenna 100 formed in a multi-layer PCB structure according to an example. The antenna 100 comprises a first SIW 102 and a second SIW 104. The first and second SIWs 102, 104 are substantially rectangular parallelepipeds and are arranged such that the second SIW 104 is positioned directly below the first SIW 102, separated by a layer 106 of electrically conductive metal, such as copper. It should be noted that edges of the first SIW and second SIW are defined by internal through-vias and blind vias filled with conductive material and not visible in Figure 1. That is, the first SIW and second SIW do not occupy the whole of the illustrated layer but at confined to a part of it by the through-vias and blind vias.

[0055] The second SIW 104 is arranged to receive an electromagnetic radiation signal from a source positioned towards one end of the second SIW 104. This is achieved via a coupling 108 that allows for transmission between the source and the second SIW 104. The source may comprise any component configured to feed the second SIW 104 with an electromagnetic signal that can be carried by the second SIW 104. For example, the source may comprise at least one of a grounded-coplanar-waveguide (GCPW), a microstrip, a stripline, and so on.

[0056] The signal is guided by the second SIW 104 to a central, internal region coupling the first SIW 102 to the second SIWs 104. The first SIW 102 comprises an array of radiating slots 110 delimited within a top or external ground plane of the first SIW 102. The radiating slots 110 allow the signal to radiate out of the antenna 100. The first SIW 102 comprises a first substrate having a first dielectric constant, Sri, and the second SIW 104 comprises a second substrate having a second dielectric constant, Sr2. Importantly, the second dielectric constant is greater than the first dielectric constant, st2 > Sri. It has been found that this relative difference in dielectric constant across the first SIW-second SIW transition may provide a more wideband impedance match than using the same dielectric constant for both the first and second SIWs 102, 104. This results in a reduction in signal reflections at the interface between the first and second SIW across a broad range of frequencies, meaning that more of the signal is transmitted to the first SIW 102 and thus radiated out of the antenna 100.

[0057] While this difference in dielectric constants leads to improved antenna performance, it has also been found that when the thickness of the second SIW 104 is greater than the thickness of the first SIW 102 a better impedance match is provided, allowing more of a signal to be transmitted across the transition. Thickness is understood as relating to the dimension of the SIW in the plane of the substrate, it is the dimension illustrated with a “z” in Figure 1. As shown in Figure 1, the thickness of the second SIW 104 is greater than the thickness of the first SIW 102.

[0058] Figure 2 shows another view of the antenna 100 in which more of the internal structure can be understood by generally showing PCB core material as transparent. In addition, a relative strength of electromagnetic radiation within the SIW is shown with shading. In this way, Figure 2 shows the internal structure of the antenna 100 and a distribution of an electric field 114 within the bottom and top ground planes of the first and second SIWs 102, 104. The coupling 110 between the signal source and the second SIW 104 can be seen as a series of blind vias filled with conductive material and arranged to couple the signal received from the source into the second SIW 104. A series of through vias 112 filled with conductive material are arranged to confine the signal within the antenna 100. In this way, the through vias 112 act as vertical walls to prevent the signal from escaping the antenna 100. Although through vias 112 are only shown in Figure 1 as being present towards the ends of the antenna 100, this is for illustration purposes only. Vias filled with conductive material are arranged to define the sides of the antenna 100 to confine the signal internally both length-ways and sideways. The coupling between the first and second SIWs 102, 104 comprises two blind vias 116 and an internal slot 118. The blind vias 116 and internal slot are positioned substantially at the centre of the first and second SIWs 102, 104, hence the first SIW 102 may is centre-fed. The blind vias 116 are arranged to define an end of the second SIW 104, while the internal slot 118 is arranged to allow transmission of the signal from the second SIW 104 to the first SIW.

[0059] While the coupling via blind vias 116 and internal slot 118 in the antenna 100 has been found to provide an efficient transition between the first and second SIWs 102, 104, other couplings could be used. For example, the coupling may comprise an E-field probe inserted into the centre of the first SIW using a via as described in “Bandwidth enhancement of substrate integrated waveguide (SIW) slot antenna with center-fed techniques,” 2011 International Workshop on Antenna Technology (iWAT), Hong Kong, China, 2011, pp. 348-351, doi: 10.1109 / IWAT.2011.5752314, M. Chen and W. Che.

[0060] In an example that has been shown to provide particularly effective impedance matching behaviour, a thickness of the first SIW 102 is 0.38mm and a thickness of the second SIW 104 is 0.49mm. The through vias 112 have a diameter of 0.30mm and a pitch (distance between neighbouring through vias) of 0.65mm. The internal slot 118 has a length 0.30mm and width 1 ,60mm. These dimensions of the internal slot 118 have been found to provide improved transmission between the first and second SIWs 102, 104. The dimensions, along with the position of through and blind vias are shown in Figure 3.

[0061] The dimensions of Figure 3 are an example only. Other constructions and dimensions may be determined using known techniques based on a desired antenna operating performance, providing that the dielectric constant associated with the second SIW is greater than the dielectric constant associated with the first SIW.

[0062] Figure 4 shows a diagrammatic representation of an example multi-layer PCB 400 in which an antenna can be implemented. For example, the antenna 100 shown in Figures 1 and 2 may be realised as the multi-layer PCB 400. For clarity, the thicknesses of all elements in the structure are shown as the same, although in practice the layers have different thicknesses as discussed in more detail below. With reference to Figure 1, the section shown in Figure 4 generally corresponds to the line A-A, showing the transition between the first SIW and the second SIW, a radiating slot and vias which define the extent of the SIW within the substrates. A top surface as illustrated in Figure 1 corresponds to a bottom surface in Figure 4 (the section of Figure 4 is inverted compared to Figure 1).

[0063] The multi-layer PCB 400 comprises six conductive PCB layers 402, 404, 406, 408, 410, 412 formed from layers of copper disposed either side of three PCB cores or laminates 414, 416, 428. The PCB laminates 414, 416, 428 are stacked on top of one another and adhered via prepreg layers 420. In practice, the prepreg layers are significantly thinner than the other layers so that in the final construction PCB layers 408 and 410 are closely adjacent to each other, as are PCT layers 404 and 406.

[0064] The first SIW, within the meaning discussed with regards to Figures 1 and 2, exists between PCB layers 408 and 412 and the second SIW exists between PCB layers 402 and 408.

[0065] The multi-layer PCB 400 comprises a plurality of through vias 422 filled with conductive material (one is shown in Figure 3 for clarity). These are equivalent to the through vias 112 of the antenna 100 shown in Figure 2. By definition, through-vias extend through the whole of the multi-layer PCB and define common edges of the first SIW and the second SIW. The multi-layer PCB 400 also comprises blind vias 424 extending from PCB layer 402 to 408, to define an end of the second SIW. These are equivalent to the blind vias 116 of the antenna 100 shown in Figure 2.

[0066] In the waveguide sections of the first and second SIWs, all of the copper has been removed from PCB layers 404, 406, and 410 so that, in use, the electric field is confined between PCB layers 402 and 408 in the second SIW and between PCB layers 408 and 412 in the first SIW. Radiating slots 428 are etched out of the copper in PCB layer 412, while the internal slots are etched out of PCB layer 408.

[0067] Example dimensions and materials of each layer are given in the table below:

[0068] Astra® MT77 is commercially available from Isola Group. RT / duroid® 5880 is commercially available from Rogers Corporation. The thicker second SIW is provided by the combination of the 0.127mm and 0.381mm Astra® MT77 laminates, which together provide a thickness of 0.508mm. These are examples of PCB materials which have been found to work well in the construction of Figures 1 to 3, the present disclosure is not limited to these materials and others can be used, providing that different Sr for the laminate is possible.

[0069] Figure 5A shows an alternative slot array antenna 500 according to an example. While the slot array of Figure 1 consisted of a single line of alternating slots either side of a common line, the slot array of Figure 5 A comprises a plurality of alternating slots 510 either side of respective common lines. The layer structure of antenna 500 is otherwise the same as Figure 1, with a different slot pattern etched on the outer layer of the structure. For the purpose of illustration only, a distribution of electric field external to the antenna is depicted in the section 514. The complete section 514, including internal field strength, can be seen in Figure 5B. A lighter area indicates a stronger field strength.

[0070] Referring to Figure 5B, it can be seen that the first SIW 502, formed from lower dielectric constant material, is thinner than the second SIW 504, formed from higher dielectric constant material. An incoming signal is coupled to the second SIW 504 at transition 506. The second SIW is coupled to the first SIW at transition 508 via blind vias and an internal slot as discussed above for Figures 1 to 3. Finally, radiation is emitted from the slots in regions 512. Figure 6 shows a plot 600 of return loss in dB on the vertical axis against frequency in GHz on the horizontal axis obtained from simulation software, CST Studio Suite in this case, for a first SIW system 602 and a second SIW system 604. The first SIW system 602 comprises a first SIW with a dielectric constant of 2.2 and a second SIW with a dielectric constant of 3, whereas the second SIW system 604 comprises SIWs with the same dimensions but a continuous / homogeneous dielectric constant of 3 throughout. The simulation is run by simulating the first SIW and second SIW of Figures 2 and 3 and the transition between the first SIW and second SIW, but omitting the radiating slots and replacing them with matched loads at both ends of the first SIW. As can be seen, the plot for the first SIW system 602 using different dielectric constants and different thicknesses shows a better than 10 dB impedance match from 69.2 (602A) - 91 GHz (602B), or equivalently a percentage bandwidth of 27.2%. On the other hand, the plot for the second SIW system 604 with constant dielectric constants but retaining different thicknesses shows a better than 10 dB impedance match from 84.8 (604A) - 94.8 GHz (604B), or equivalently, a percentage bandwidth of 11.1%.

[0071] On Figure 6, return loss is shown as a negative number in dB reflecting that the reflected signal is lower than the input signal. (References to a greater return loss mean that the reflected portion of the signal is smaller, a greater return loss is preferred so that as much of the signal as possible is transferred from the second SIW to the first SIW.) This provides an effective demonstration of the wideband performance of the transition from the second SIW to the first SIW in systems according to the present disclosure.

[0072] The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, although antenna structures have been described, the present disclosure applies to any RF device or apparatus connecting two SIWs via a centre or “Tee” junction. By omitting the radiating slots, other embodiments may be used in RF filters, for example.

[0073] Additionally, it is understood that the multiple SIW systems as described herein may be arrayed together. For instance, multiple of the antennas illustrated in Figs 1-3, 5 A and 5B may be positioned adjacently to operate together to provide enhanced electromagnetic performance. The feed structure being positioned behind the first SIW allows adjacent antennas to be spaced at an SIW pitch of substantially half the operating wavelength. Adjacent antennas may share a via wall, allowing the SIW pitch required for operation at a predetermined wavelength to be maintained.

[0074] It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

CLAIMS1. A substrate-integrated-waveguide, SIW, system, wherein the SIW system is an antenna or radio frequency filter, the SIW system comprising: a first SIW comprising a first substrate having first dielectric constant; and a second SIW coupled to the first SIW substantially at a centre of the first SIW such that the first SIW is a centre-fed SIW and comprising a second substrate having a second dielectric constant which is greater than the first dielectric constant.

2. The SIW system of claim 1, wherein the first dielectric constant is between 10% to 40% less than the second dielectric constant.

3. The SIW system of any preceding claim, wherein the first dielectric constant is less than or equal to 3.

4. The SIW system of any preceding claim, wherein the first substrate has a thickness which is less than a thickness of the second substrate.

5. A substrate-integrated-waveguide, SIW, system, wherein the SIW system is an antenna or radio frequency filter, the SIW system comprising: a first SIW comprising a first substrate having a first thickness; and a second SIW coupled to the first SIW substantially at a centre of the first SIW such that the first SIW is a centre-fed SIW and comprising a second substrate having a second thickness which is greater than the first thickness.

6. The SIW system of any preceding claim, having a return loss for signals travelling from the second SIW to the first SIW of at least lOdB across a bandwidth percentage of at least 10% about a centre frequency.

7. The SIW system of any preceding claim, having a return loss for signals travelling from the second SIW to the first SIW of at least 10 dB across a bandwidth of at least 10 GHz.

8. The SIW system of any preceding claim, wherein a transition between the first and second SIWs comprises a blind via and an internal slot, each positioned substantially at the centre of the first SIW.

9. The SIW system of any preceding claim, further comprising a grounded- coplanar- waveguide, GCPW, arranged to feed the second SIW with electromagnetic radiation.

10. The SIW system of any preceding claim, implemented in a multi-layer printed circuit board comprising at least three layers.

11. The SIW system of any preceding claim, comprising a plurality of through-hole vias that are arranged to confine a signal within at least one of the first SIW and the second SIW.

12. The SIW system of any preceding claim, wherein the first and second SIWs are arranged such that the second SIW feeds the first SIW from behind the first SIW.

13. The SIW system of any preceding claim, wherein the SIW system is an antenna, and wherein the first SIW is configured to radiate electromagnetic radiation via a plurality of radiating slots.

14. A system comprising a first SIW system according to any preceding claim and a second SIW system according to any preceding claim, wherein the first SIW system is positioned adjacent to the second SIW system.

15. The system of claim 14, configured to operate with electromagnetic radiation having a predetermined wavelength, and wherein the first SIW system is spaced at a pitch of substantially half the predetermined wavelength from the second SIW system.

16. The system according to claim 14 or claim 15, wherein the first SIW system comprises a plurality of through-hole vias that are arranged to confine a signal within at least one of the first SIW and the second SIW, and wherein the second SIW system shares the plurality of through-hole vias with the first SIW system.

17. A transceiver including the SIW system of claim 13 or the system of any of claims 14 to 16 when dependent on claim 13.

18. A radar system comprising the transceiver of claim 17.

19. A radio frequency system comprising the SIW system of any of claims 1 to 12 or the system of any of claims 14 to 16 when dependent on any of claims 1 to 12.

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