Method and structure for reducing air waveguide antenna leakage

Abstract

Methods and structures are provided for reducing air waveguide antenna leakage. A cavity is used within one or both halves of a split planar antenna so that parallel plate mode energy leakage from an air waveguide of the antenna through an air gap between the two halves can be controlled by redirecting the parallel plate mode energy leakage back to the air gap or blocking it from an adjacent antenna. Therefore, the radio frequency performance of the antenna is improved. An air waveguide antenna, a method of manufacturing the air waveguide antenna, and an automotive radar including the air waveguide antenna are described.

Description

Technical Field

[0001] The present disclosure relates to air waveguide antennas, vehicle radars including the same, and methods of manufacturing the same. The present disclosure relates to reducing leakage in air waveguide antennas, particularly by applying cavities to the antenna structure to return parallel plate mode energy leakage back to the air waveguide and / or redirect the leaked energy away from adjacent antennas. Background Art

[0002] Vehicle radars include a front-end antenna that transmits electromagnetic waves into free space and receives reflections from surrounding surfaces to detect nearby objects, such as vehicles. Common technologies used to construct such vehicle radars and route the electromagnetic waves along transmission lines between free space and processing circuitry are based on microstrip and substrate-integrated waveguide (SIW) technologies. Both technologies require a dielectric substrate, which is lossy and reduces antenna gain.

[0003] Air waveguide antennas have been developed to address the shortcomings associated with using a substrate, allowing electromagnetic waves to be guided through an air-filled structure rather than a solid structure. Such antennas are typically made from injection-molded metallized plastic or solid metals such as aluminum or magnesium. The injection molding process is used to form each of the two antenna halves, or "pieces," which are brought together to complete the antenna. Waveguide portions are formed in opposing surfaces of each part, so that when the two antenna halves are brought together, the waveguide portions of each antenna component face each other to complete the waveguide.

[0004] Figure 1 An example of a cross-section of a typical "split block configuration" is shown, in which the upper and lower antenna components are brought together so that the upper and lower waveguide sections face each other to complete the waveguide. During the injection molding process applied to each antenna component, manufacturing tolerances and warping mean that the opposing surfaces of the upper and lower antenna components do not fit together precisely. In practice, an air gap exists between the two antenna components. The air gap is non-uniform, typically ranging from 0 μm to 85 μm, but can be greater than 100 μm in some areas. In this disclosure, such gaps are referred to as "microgaps."

[0005] This microgap is undesirable and can be minimized through mechanical measures, such as using screws to tightly secure the two antenna parts together. However, over the lifetime of the antenna, the size of the microgap may change due to, for example, thermal expansion and contraction. Manufacturing the antenna components in a manner that ensures robustness to such changes is difficult.

[0006] A waveguide is insensitive to microgaps if the microgaps exist in regions where the current associated with the electromagnetic waves carried by the waveguide is zero. Thus, for rectangular waveguides, it is beneficial to configure the antenna so that the split plane between the two antenna elements lies in the horizontal (xy) electric field plane of the waveguide, as shown in FIG. Figure 1 In this way, if the propagation direction of the electromagnetic wave is perpendicular to the cross section of the waveguide (y direction), so that the waveguide is a horizontal waveguide, no current in the waveguide wall crosses the microgap, and no electromagnetic energy leaks through the microgap.

[0007] However, if the propagation direction of the electromagnetic wave is vertical (z direction), which may occur at the portion of the antenna where the electromagnetic wave is carried to free space via the feeding or radiating slot, or is carried to or from the monolithic microwave integrated circuit (MMIC), then since the current across the micro gap is not zero, there is leakage of electromagnetic energy through the micro gap, such as Figure 2 As shown. This leakage is referred to herein as parallel plate mode energy leakage or parasitic parallel plate mode leakage between the substantially parallel plates of the upper and lower antenna elements. This leakage degrades the radio frequency (RF) performance of the antenna due to reduced gain, angular coverage, signal-to-noise ratio, and the introduction of undesirable antenna-to-antenna coupling and crosstalk.

[0008] In the embodiments set forth in this disclosure, countermeasures are described based on adding structure to air waveguide antennas that can reduce and in some cases eliminate the effects of such parallel plate mode energy leakage by redirecting the energy leakage into the air waveguide and / or blocking leakage to adjacent antennas. Summary of the Invention

[0009] According to a first aspect, a method for manufacturing an air waveguide antenna is provided, wherein the air waveguide antenna is formed by a first antenna part and a second antenna part, the first antenna part including a first surface having a first air waveguide part therein, the second antenna part including a second surface having a second air waveguide part therein, the method comprising the following steps: forming one or more cavities in one or both of the first surface and the second surface; and assembling the first antenna part and the second antenna part together with the first surface and the second surface facing each other, so that the first air waveguide part and the second air waveguide part are opposite to each other to form an air waveguide; wherein the one or more cavities redirect parallel plate mode energy leakage of electromagnetic waves guided by the air waveguide through an air gap between the assembled first surface and the second surface.

[0010] In this manner, an effective, cost-neutral countermeasure to leakage effects is provided. The reduction in leakage can improve RF performance by at least one of maintaining signal gain, maintaining antenna angular coverage, increasing signal-to-noise ratio, and reducing undesirable antenna-to-antenna coupling and crosstalk. Furthermore, the likelihood that antennas manufactured by the process will fail to meet required performance standards and therefore be scrapped is reduced, thereby improving the yield of the manufacturing process.

[0011] In an embodiment, the one or more cavities include a cavity disposed adjacent to the respective first air waveguide portion or the second air waveguide portion such that the parallel plate mode energy leakage is reflected back into the air waveguide.

[0012] In an embodiment, the method includes forming the one or more cavities to have dimensions according to the frequency of the electromagnetic wave to be guided by the air waveguide so that the reflected energy is in phase with the guided electromagnetic wave. In this manner, the reflected energy constructively interferes with the guided wave, and thus the characteristics of the guided wave can be preserved.

[0013] In an embodiment, the method includes forming the one or more cavities at locations on the first surface and / or the second surface to reduce crosstalk between the air waveguide and one or more further air waveguides of one or more corresponding further antennas. In this way, signal coupling between different antenna feed lines, such as transmit and receive paths, can be reduced or eliminated.

[0014] In an embodiment, the method includes forming the one or more cavities to extend in an orientation along the first surface and / or the second surface such that parallel plate mode energy leakage in a direction perpendicular to the extent of the one or more cavities is blocked. In this way, both the position of the one or more cavities and their orientation can be used to optimize the blocking of parallel plate mode energy leakage for a particular situation.

[0015] In an embodiment, the method includes forming one or more cavities in the first surface and forming one or more cavities in the second surface, wherein when the first antenna portion and the second antenna portion are assembled together, none of the one or more cavities in the first surface aligns with a cavity in the second surface. In this way, cavity positions can be alternated between the first and second surfaces, which provides manufacturing advantages in addition to optimizing space usage.

[0016] In an embodiment, the one or more cavities have a depth of 0.5 mm to 0.9 mm, and in particular 0.7 mm.

[0017] In an embodiment, the method includes forming the one or more cavities adjacent to a transition portion of the air waveguide for guiding electromagnetic waves from the antenna to free space or to a monolithic microwave integrated circuit. Since such a gap between the first antenna portion and the second antenna portion in such a region is associated with significant parallel plate mode energy leakage, arranging the one or more cavities proximate to such a region increases the effectiveness of blocking leakage.

[0018] In an embodiment, the first antenna portion is an upper antenna portion and the second antenna portion is a lower antenna portion, and the vertical center of each cavity of at least one of the one or more cavities, in a direction extending between the upper antenna portion and the lower antenna portion, is horizontally aligned with the vertical center of the transition portion of the air waveguide. This alignment optimizes reflection of electromagnetic energy back into the waveguide.

[0019] In an embodiment, the transition between the first surface or the second surface and the sidewall of the cavity is curved.In this way, the mechanical integrity of the surface of the antenna part is improved.

[0020] In an embodiment, the method comprises forming the one or more cavities using injection molding.In this way, the cavities can be introduced into the antenna structure as part of the same process as forming the antenna components and waveguide routing.

[0021] According to a second aspect, an air waveguide antenna is provided, comprising: a first antenna part and a second antenna part, the first antenna part comprising a first surface having a first air waveguide part therein, the second antenna part comprising a second surface having a second air waveguide part therein; and one or more cavities in one or both of the first surface and the second surface; wherein the first antenna part and the second antenna part are arranged to be assembled together with the first surface and the second surface facing each other, so that the first air waveguide part and the second air waveguide part are opposite to each other to form an air waveguide; wherein the one or more cavities redirect parallel plate mode energy leakage of electromagnetic waves guided by the air waveguide through the air gap between the assembled first surface and the second surface.

[0022] In this manner, an antenna is provided in which the effects of parallel plate mode energy leakage on angular coverage, signal gain, and lifetime performance variations are reduced or eliminated.

[0023] In an embodiment, the one or more cavities include a cavity disposed adjacent to the respective first air waveguide portion or second air waveguide portion such that the parallel plate mode energy leakage is reflected back into the air waveguide.

[0024] According to a third aspect, a vehicle radar is provided, comprising the air waveguide antenna according to the above-described embodiment, wherein the air waveguide includes a transition portion for guiding electromagnetic waves emitted from the antenna into free space or into a monolithic microwave integrated circuit (MMIC), and at least one of the one or more cavities is disposed adjacent to the transition portion of the air waveguide. Because such a gap between the first antenna portion and the second antenna portion in such a region is associated with significant parallel plate mode energy leakage, arranging the one or more cavities proximate to such a region increases the effectiveness of blocking leakage.

[0025] According to a fourth aspect, a vehicle radar is provided, comprising a plurality of antennas being the above-mentioned air waveguide antennas, wherein the one or more cavities are arranged between each of the plurality of antennas to reduce crosstalk between the plurality of air waveguide antennas. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Illustrative embodiments will now be described with reference to the accompanying drawings, in which:

[0027] Figure 1 shows an example of a cross section of a split-block antenna configuration with a horizontal air waveguide;

[0028] Figure 2 shows an example of a cross section of a split-block antenna configuration with a vertical air waveguide;

[0029] Figure 3 shows a cross section of an air waveguide antenna according to a first embodiment;

[0030] Figure 4 shows a plan view of the lower antenna portion of the first embodiment;

[0031] Figure 5 illustrates the effect of a blocking cavity on the propagation of parallel plate mode energy leakage from an air waveguide antenna according to an embodiment;

[0032] Figure 6 A plan view showing a lower antenna portion of an air waveguide antenna according to a second embodiment;

[0033] Figure 7 shows a comparison of the effect of a blocking cavity on energy leakage from an air waveguide antenna in an embodiment;

[0034] Figure 8 shows a comparison of the effects of the blocking cavity on the forward transmission scattering parameters of the air waveguide antenna according to the third embodiment;

[0035] Figure 9shows a comparison of the effect of the blocking cavity on the input reflection scattering parameter of the air waveguide antenna according to the third embodiment; and

[0036] Figure 10 A manufacturing process according to a fourth embodiment is shown. DETAILED DESCRIPTION

[0037] Figure 3 FIG. 1 shows a cross section of an air waveguide antenna 30 according to a first embodiment. Air waveguide antenna 30 is formed of a first antenna portion 31 and a second antenna portion 32. The first and second antenna portions are assembled together such that a first surface 33 of first antenna portion 31 faces a second surface 34 of second antenna portion 32. A microgap 35 exists between first surface 33 and second surface 34.

[0038] For simplicity, the micro-gap 35 is illustrated as being uniform, but the size of the micro-gap 35 may vary along the length or width of the air waveguide antenna 30 .

[0039] The first surface 33 includes a first waveguide portion 36, and the second surface 34 includes a second waveguide portion 37. Each of the first antenna portion 31 and the second antenna portion 32 is formed by injection molding, including forming the contours of the first waveguide portion 36 and the second waveguide portion 37 in a manner known in the art. The first waveguide portion 36 is opposite to the second waveguide portion 37 to form an air waveguide 38. The first waveguide portion 36 is open at the lower surface of the first antenna portion 31 to transmit electromagnetic waves to and from the MMIC (not shown) below the air waveguide antenna 30. The MMIC can process and generate signals for propagation as electromagnetic waves through the air waveguide 38. In this way, the propagation direction of the electromagnetic waves in the air waveguide 38 is Figure 3 In the illustration of , it is in the vertical z direction. In this disclosure, such an air waveguide is referred to as a vertical transition.

[0040] Adjacent to the air waveguide 38 are cavities 39a, 39b. Figure 3 Two cavities are illustrated in FIG. In other embodiments, more than two cavities are employed, and in some embodiments as few as one cavity may be employed. Figure 3 In the first embodiment shown, the cavities 39a, 39b are in the first antenna portion 31. In other embodiments, one or more cavities are arranged in the second portion 32. In other embodiments, one or more cavities are arranged in each of the first antenna portion 31 and the second antenna portion 32.

[0041] In this disclosure, the term "adjacent" should not be interpreted as limiting the spacing between the cavities 39a, 39b and the waveguide 38 to any particular lateral distance in the horizontal x-direction, although it is preferred to use as small a distance as is physically possible within the limits of the manufacturing process for producing the air waveguide antenna of the first embodiment. In some embodiments, for metal-based air waveguide antennas (using, for example, magnesium), the manufacturing limit is on the order of 0.8 mm.

[0042] In some embodiments, a plurality of cavities are formed on each of the left and right sides of the waveguide 38, wherein the plurality of cavities are arranged in order with a first cavity closest to the air waveguide 38, a second cavity adjacent to the first cavity but farther away from the air waveguide 38 than the first cavity, etc. In this case, the cavity closest to the air waveguide 38 can be considered to be adjacent to the air waveguide 38.

[0043] In the first embodiment, the depth of each cavity 39a, 39b is between 0.5 mm and 0.9 mm, preferably 0.7 mm. Each cavity 39a, 39b has a width of about 0.8 mm, and thus the cavity width is comparable to the spacing from the air waveguide 38 to the cavity 39a, 39b.

[0044] Figure 4 A plan view of the first antenna portion 31 according to a first embodiment is shown. When viewed in plan view, the arrangement of the cavities 39a, 39b and the air waveguide 38 is such that the central axis of the vertical transition 40 of the air waveguide 38 is aligned with the central axis of the cavities 39a, 39b in the y-direction. Thus, a line substantially parallel to the x-direction can be drawn connecting the central axis of the vertical transition of the air waveguide 38 with the central axis of the cavities 39a, 39b. In some embodiments, the openings of the cavities 39a, 39b in the first surface 33 are rectangular, having a longer length in the y-direction than in the x-direction, and the central axis of the cavities 39a, 39b corresponds to the position of the center of the longer y-direction dimension.

[0045] Aligning the cavities 39a, 39b with the air waveguide 38 in this manner can optimize the RF performance of the air waveguide antenna 30, but the cavities 39a, 39b do not necessarily need to be aligned with the air waveguide 38 in this manner. Instead, the cavities can be positioned so that they exist at a desired spacing on a radius extending in any outward direction from the air waveguide.

[0046] In particular, the cavities may be distributed at additional "free" locations of the antenna that are not adjacent to vertical transitions in order to block leakage of electromagnetic energy in specific directions, as will be described below.

[0047] exist Figure 3In the illustrated embodiment, curved transitions are formed in the sidewalls of cavities 39a, 39b in the region where they interface with first surface 33. This curved transition enhances the mechanical integrity of antenna portion 31 by avoiding sharp discontinuities in first surface 33 that could otherwise present a risk of fracture. First waveguide portion 36 and second waveguide portion 37 also exhibit this curved transition.

[0048] As mentioned above Figure 2 As described, when the electromagnetic wave travels through the air waveguide 38, parallel plate mode energy leakage occurs through the micro gap 33. The energy leakage propagates to the cavities 39a, 39b, which serve to reflect most of the energy leakage back to the waveguide 38. Specifically, the electromagnetic energy enters the cavities 39a, 39b and resonates as electromagnetic waves within the cavities 39a, 39b. A portion of the electromagnetic wave is reflected back from the bottom of the cavities 39a, 39b along the micro gap 33 toward the air waveguide 38. The energy returning to the air waveguide 38 combines with the guided electromagnetic wave, so that the characteristics of the electromagnetic guided wave (represented as amplitude, phase, and frequency components) are close to the state that would exist in the absence of leakage. Therefore, the resonant cavity substantially blocks the energy leakage from the air waveguide antenna.

[0049] Figure 5 Simulations comparing the propagation of electric and magnetic fields in different configurations are illustrated. Figure 5 (a) shows a plan view of an ideal reference case, comprising an air waveguide 50 with two vertical transitions 51 and 52. There are no microgaps, resulting in a completely enclosed waveguide. Waveguides of this structure can be formed using techniques such as additive manufacturing, but this is less suitable for large-scale production than the injection molding techniques used in the embodiments. In this reference case, no energy leaks from the air waveguide 50. The electric and magnetic fields are contained within the waveguide, and the cavity has no influence.

[0050] Figure 5 (b) shows the Figure 5 (a) The same air waveguide 50, but where the air waveguide antenna structure is such that there is a micro gap of 150 μm between the two antenna halves. In this example there is no cavity, and therefore,

[0051] Figure 5 (b) shows a conventional configuration, compared to which this embodiment has superior performance. The leakage of electric and magnetic fields from the transition section is visible as a region of energy propagating outward from the waveguide, although its amplitude is lower than the amplitude of the energy contained within the waveguide.

[0052] Figure 5 (c) shows Figure 5(b) An air waveguide in which the resonant cavities 53, 54 are located adjacent to the transition sections 51, 52. Here, it can be seen that the leakage of the electric and magnetic fields from the transition sections 51, 52 of the waveguide is significantly reduced, so that the overall leakage is represented by a small area of ​​low intensity, which is consistent with the Figure 5 Thus, it can be seen that the cavities 53, 54 are a particularly effective solution to the problem of parallel plate mode energy leakage that exists in mass-produced antennas constructed from two halves.

[0053] Figure 6 A plan view of a lower antenna portion 61 of an air waveguide antenna 60 of a second embodiment is shown. The lower antenna portion 61 includes two antenna elements fed by two respective waveguides, each antenna element being associated with four radiating antenna slots. A first waveguide 62 extends substantially horizontally from a first vertical transition 63 to a MMIC (not shown) toward a first group 64 of four vertical radiating antenna slots, which may represent a portion of a transmitting antenna or a receiving antenna. A second waveguide 65 extends from a second vertical transition 66 toward a second group 67 of four vertical antenna slots. Similarly, the second group 67 may represent a portion of a transmitting antenna or a receiving antenna, and Figure 6 In FIG, the second group 67 is illustrated as part of a receiving antenna.

[0054] Lower antenna section 61 includes cavities 68a and 68b adjacent to vertical transitions 63 and 66, and cavity 69 adjacent to antenna slot groups 64 and 67. Cavity 68a is used to reflect leakage back into air waveguide 62. Cavity 68b is used to reflect leakage back into air waveguide 65. Cavity 69 blocks leakage between the two antenna elements and also reflects leakage back into waveguides 62 and 63.

[0055] Depend on Figure 6 The reduced coupling between antennas achieved by the configuration can help prevent or substantially minimize crosstalk between two transmit antennas, two receive antennas, or a transmit antenna and a receive antenna, depending on the specific configuration used. More generally, one or more of the cavities can be positioned to prevent electromagnetic energy from leaking in a particular direction.

[0056] For ease of description, Figure 6 The representations illustrated in are simplified. In practice, the specific number and positions of the cavities should be adjusted to optimize the suppression of specific coupling paths, taking into account the fabrication constraints imposed by the material choice.

[0057] Figure 7 In the case where the lower antenna portion is separated from the upper antenna portion by a micro gap of 100 μm, reference is made to a similar Figure 6 The waveguide layout shown in FIG. 1 is a waveguide layout illustrating the principle of targeted attenuation of electromagnetic energy.

[0058] Figure 7 (a) shows an example of a waveguide 70 feeding four radiating slots, without adjacent cavities. The propagation of electric field energy in the microgaps is illustrated in the field intensity diagram along with the higher intensity electric field energy of the waveguide itself. Energy leakage occurs in well-defined directions from the radiating slots, so in embodiments, cavities extending (individually or as a group) perpendicular to the expected energy leakage direction can be introduced.

[0059] Figure 7 (b) shows the Figure 7 (a) Same waveguide arrangement as in (a), but here, a set of cavities 71 is added near the radiating slot, which are arranged at an angle perpendicular to the main leakage direction 73, as shown in Figure 7 As shown in (a). Each cavity of group 71 has a rectangular opening, and for the purpose of describing this embodiment, the longer side of the rectangular opening defines the orientation of the cavity's extent. The cavities are arranged in two rows of three, with each row extending in the same direction as the longitudinal extent of the cavity. Figure 7 (b) shows that there is a significant reduction in leakage in a direction towards the upper left of the figure, which is perpendicular to the orientation of the cavity 71.

[0060] Figure 7 (c) illustrates Figure 7 An extension of the principle shown in (b) where another set of 72 cavities is added to reduce leakage towards the upper right of the cavity.

[0061] Figure 8 A simulation comparison of the effect of a blocking cavity according to a third embodiment on the forward transmission scattering parameter (S parameter) (commonly referred to as the S2,1 parameter) of an air waveguide antenna is shown. The simulation is based on a metal air waveguide transmission line having a vertical transition section formed in two antenna halves separated by a 0.15 mm air gap.

[0062] Figure 8 Three curves are shown in Figure 1, representing the S2,1 parameter as a function of frequency for the attenuation of a wave guided by an air waveguide. The dashed line 80 represents the reference case with no air gap and therefore no energy leakage from the air waveguide. There is a minimum attenuation between 76 and 81 GHz, where the curve approaches 0 dB.

[0063] The second curve 81 shows the effect of introducing a 0.15 mm air gap without introducing a cavity. The electromagnetic wave is more attenuated at all frequencies, with significant attenuation starting at 80 GHz.

[0064] The third curve 82 shows the effect of introducing a cavity into the system for the second curve, where the cavity is e.g. Figure 3The cavity is positioned such that the reflection of energy into the waveguide is in phase with the electromagnetic wave guided by the waveguide.

[0065] Compared to the second curve, the attenuation is reduced, showing the effect of reflecting energy back to the vertical transition. Comparing the relative attenuation of the second and third curves shows that more than 50% of the energy is recovered, providing sufficient bandwidth for 76 to 81 GHz operation.

[0066] Figure 9 The barrier cavity is shown according to the above Figure 8 A simulation comparison of the influence of the input reflection scattering parameter (commonly referred to as the S1,1 parameter) of the air waveguide antenna of the third embodiment is described.

[0067] The S1,1 parameter can be considered in terms of electromagnetic wave reflections back to the MMIC caused by impedance mismatch. For the reference case 90 without an air gap, it can be seen that the impedance matching results in significant attenuation of reflections at 75.6 GHz and 77.8 GHz. The second curve 91 illustrates the effect of introducing an air gap, which shows a reduction in attenuation of reflections up to 79.5 GHz. The third curve 92 illustrates the effect of the cavity in addition to the air gap, showing a slight reduction in reflections and, therefore, a slight improvement in impedance matching. Therefore, the cavity does not negatively impact impedance matching.

[0068] To optimize performance, it is desirable to reflect electromagnetic energy back into the waveguide in phase with the electromagnetic energy carried by the waveguide. This ensures that the reflected energy constructively interferes with the guided electromagnetic wave. If there are elements of destructive interference between the reflected electromagnetic wave and the guided electromagnetic wave, the amplitude and other properties of the guided electromagnetic wave will be reduced.

[0069] In embodiments, some destructive interference can be tolerated, as the overall reduction in parallel-plate mode energy leakage can outweigh the reduction in S2,1 attenuation of the guided electromagnetic wave. Furthermore, the reduction in coupling between different antenna paths can be more beneficial than a 0.5 dB reduction in S2,1 attenuation. For cavities located away from the waveguide, for example, to shield an antenna from another antenna, the blocking function may be more important than returning energy to the waveguide. Therefore, it is not necessary for the reflected energy to be in phase with the guided electromagnetic wave.

[0070] In the case of in-phase reflection, this is achieved by considering the distance between the cavity and the waveguide, which is configured so that the distance of the electromagnetic wave reflected from the waveguide to the bottom of the cavity is a multiple of the wavelength. By adopting such a configuration, a phase separation of 360° or multiples of 360° is achieved.

[0071] It should be understood that the embodiments shown above illustrate applications for illustrative purposes only. In practice, the embodiments can be applied to many different configurations, and given the teachings set forth in this disclosure, the detailed embodiments are straightforward for those skilled in the art to implement. A specific operating configuration can be designed and optimized from mathematical simulations, taking into account the antenna's operating frequency, the physical materials used, and the desired micro-gap size.

[0072] Vehicle radar antennas are particularly suitable applications for the air waveguide antenna of the described embodiment. Such antennas typically operate in the 76 to 77 GHz range. Magnesium is a suitable material for the antenna, but aluminum or metalized plastics are also suitable.

[0073] Based on full-wave simulations performed by the inventors, it has been found that the effectiveness of the cavity is independent of whether it is located in the upper or lower half of the antenna structure. Typically, the upper half of the antenna structure is associated with the radiating aperture or slot, through which electromagnetic waves are transmitted to or received from free space. The lower half of the antenna structure is typically associated with the MMIC and underlying processing electronics. However, performance simulations have shown that there is flexibility in placing the cavity in the upper or lower half, allowing the location to be optimized to account for the spatial constraints imposed by the waveguide routing.

[0074] In particular, an effective configuration is one in which the cavities are arranged on both the upper and lower antenna sections in an alternating or staggered configuration, such that the cavities on one section do not overlap with the cavities on the other section. This arrangement can optimize the use of space, allowing the cavities to be positioned closer together than if they were arranged on the same antenna section, given material constraints (such as minimum allowable wall thickness) and cavity sidewall curve specifications. The ability to distribute the cavities on both sections of the antenna is advantageous when combined with specific features such as directional attenuation, and for complex waveguide routing structures that employ slotted waveguides or fine antenna slots. Conversely, if there is an overlap of cavities, this can represent a redundant arrangement of the cavities, as it has been found that having two overlapping cavities at the same spacing from the waveguide does not improve performance.

[0075] In summary, the use of a cavity enables a cost-neutral countermeasure against leakage effects due to the air gap between the antenna pieces.By applying a resonant cavity in one or both halves or antennas, the propagating parallel plate modes in the air gap can be controlled and redirected.

[0076] The improvement in RF performance achieved can be expressed in a variety of ways, particularly a reduction in signal loss and gain degradation due to leakage, maintenance of angular coverage for devices such as radars, an increase in signal-to-noise ratio, and a reduction in inter-antenna coupling. This reduction in crosstalk applies whether considering multiple antennas on the same device (such as the transmit / receive antennas of a radar) or considering the intention to position an antenna near another antenna as part of a larger system design. In addition, air waveguide antennas produced with this configuration are more likely to meet the performance specifications required by their target devices (such as vehicle antennas), thereby reducing component waste.

[0077] Furthermore, the reduction in parallel plate mode energy leakage makes the air waveguide antenna of embodiments more robust to variations in the air gap over the lifetime of the antenna. Such variations may occur due to, for example, thermal expansion and contraction. Without the cavity of embodiments, variations in the air gap size would cause performance fluctuations in equipment such as a radar containing the antenna, potentially introducing blind spots or regions of additional azimuth and elevation errors at specific angular azimuth or elevation positions where leakage is sufficient to cause the radar to fall outside its originally calibrated operating range.

[0078] As described above, the method of manufacturing an air waveguide antenna according to an embodiment can begin after providing a first antenna portion and a second antenna portion, each of which includes a first waveguide portion and a second waveguide portion within respective first and second surfaces. According to an embodiment, the method includes adding cavities at desired locations before assembling the antenna portions together, thereby significantly reducing or eliminating any parallel plate mode energy leakage that would otherwise be introduced after the antenna portions are assembled together. In some embodiments, the cavity is formed in the antenna portion simultaneously with the waveguide portion, allowing both the waveguide routing and the cavity layout to be achieved during the same injection molding process, which improves the efficiency of the manufacturing process.

[0079] Figure 10 The manufacturing process according to the fourth embodiment is illustrated. In step S101, two antenna sections are provided, each comprising a waveguide section to be combined to form an air waveguide. Process parameters are determined to identify the location of one or more cavities that will reduce parallel plate mode energy leakage when the two antenna sections are assembled.

[0080] Such process parameters include material parameters and the desired operating frequency, which influence cavity dimensions. The resonant frequency of the cavity itself depends on the dimensions, and the lateral spacing of the cavity from the air waveguide affects the phase of the reflected energy. The position of the waveguide can take into account the desired leakage reduction, based on the principle that any reduction in leakage represents an improvement in RF performance over conventional systems and may not require the introduction of more cavities than required.

[0081] Furthermore, the positioning of the cavity on the surface of the antenna part is affected by consideration of the required minimization of inter-antenna coupling and the directionality of such minimization.

[0082] Another parameter to consider is the expected gap size that will occur after the two antenna parts are assembled together, the variability of the gap size, and the predicted evolution of the gap size over the product's lifetime. This information can be derived from the manufacturing tolerances associated with the processes and material specifications used to form the antenna parts. Historical manufacturing data can also be analyzed to derive previous gap sizes resulting from similar configurations. Mathematical simulation can also be employed.

[0083] The analysis of S101 is achieved by mathematical simulation using a computer executable program.

[0084] In step S102 , a cavity is formed using an injection molding process.

[0085] In step S103 , the two antenna parts are assembled together to form an air waveguide antenna.

[0086] It should be understood that in embodiments, the information and analysis required in step S101 can be performed by an external system, and the required information can simply be input into the manufacturing process of the embodiments. In this sense, step S101 is not essential to the embodiments. In step S102, alternatives to injection molding are also possible, such as etching, laser cutting, stamping, and additive manufacturing.

Claims

1. A method for manufacturing an air waveguide antenna, the air waveguide antenna being formed of a first antenna portion and a second antenna portion, the first antenna portion including a first surface having a first air waveguide portion therein, the second antenna portion including a second surface having a second air waveguide portion therein, the method comprising the following steps: forming one or more cavities in one or both of the first surface and the second surface; and assembling the first antenna portion and the second antenna portion together with the first surface and the second surface facing each other so that the first air guide portion and the second air guide portion oppose each other to form an air guide; The one or more cavities redirect parallel plate mode energy leakage of electromagnetic waves guided by the air waveguide through the air gap between the assembled first and second surfaces.

2. The method according to claim 1, wherein The one or more cavities include a cavity positioned adjacent to the respective first air waveguide portion or the second air waveguide portion such that the parallel plate mode energy leakage is reflected back into the air waveguide.

3. The method according to claim 1 or 2, further comprising: The one or more cavities are formed to have dimensions according to the frequency of the electromagnetic wave to be guided by the air waveguide so that the reflected energy is in phase with the guided electromagnetic wave.

4. The method according to claim 1 or 2, further comprising: The one or more cavities are formed at locations on the first surface and / or the second surface to reduce crosstalk between the air waveguide and one or more further air waveguides of one or more corresponding further antennas.

5. The method according to claim 4, further comprising: The one or more cavities are formed to extend in an orientation along the first surface and / or the second surface such that parallel plate mode energy leakage in a direction perpendicular to the extent of the one or more cavities is blocked.

6. The method according to claim 1 or 2, wherein: The step of forming the one or more cavities includes forming one or more cavities in the first surface and forming one or more cavities in the second surface, wherein when the first antenna part and the second antenna part are assembled together, none of the one or more cavities in the first surface are aligned with the cavity in the second surface.

7. The method according to claim 1 or 2, wherein: The one or more cavities have a depth of 0.5mm to 0.9mm, optionally 0.7mm.

8. The method according to claim 1 or 2, further comprising: The one or more cavities are formed adjacent to a transition portion of the air waveguide for guiding electromagnetic waves from the antenna to free space or to a monolithic microwave integrated circuit (MMIC).

9. The method according to claim 8, wherein The first antenna portion is an upper antenna portion, and the second antenna portion is a lower antenna portion, and a vertical center of each cavity of at least one of the one or more cavities in a direction extending between the upper antenna portion and the lower antenna portion is horizontally aligned with a vertical center of the transition portion of the air waveguide.

10. The method according to claim 1 or 2, wherein: The transition between the first surface or the second surface and the sidewall of the cavity is curved.

11. The method of claim 1 or 2, further comprising forming the one or more cavities using injection molding.

12. An air waveguide antenna, comprising: a first antenna portion and a second antenna portion, the first antenna portion including a first surface having a first air guide portion therein, the second antenna portion including a second surface having a second air guide portion therein; and one or more cavities in one or both of the first surface and the second surface; wherein the first antenna portion and the second antenna portion are arranged to be assembled together with the first surface and the second surface facing each other, so that the first air waveguide portion and the second air waveguide portion are opposite to each other to form an air waveguide; The one or more cavities redirect parallel plate mode energy leakage of electromagnetic waves guided by the air waveguide through the air gap between the assembled first and second surfaces.

13. The air waveguide antenna according to claim 12, wherein: The one or more cavities include a cavity positioned adjacent to the respective first air waveguide portion or second air waveguide portion such that the parallel plate mode energy leakage is reflected back into the air waveguide.

14. A vehicle radar, comprising the air waveguide antenna according to claim 12 or claim 13, wherein: The air waveguide includes a transition portion for guiding electromagnetic waves from the antenna to free space or to a monolithic microwave integrated circuit (MMIC), and at least one of the one or more cavities is disposed adjacent to the transition portion of the air waveguide.

15. A vehicle radar comprising a plurality of antennas that are the air waveguide antennas according to claim 12 or claim 13, wherein: The one or more cavities are disposed between respective antennas of the plurality of antennas to reduce crosstalk between the plurality of antennas.

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