Low sidelobe level integrated cavity backslot array antenna system

Abstract

The antenna system operates in a hybrid coplanar waveguide and rectangular waveguide mode. A slot array having a conductive layer is disposed on a substrate and defines a coplanar waveguide that connects a plurality of side slots arranged in a row to form a slot array. Another substrate is spaced apart from the substrate and defines a ground plane thereon. A defined volume waveguide is disposed between the substrates. The array is configured to radiate a radiation pattern in a hybrid mode, the radiation pattern being generated by the combination of the slot array and the defined volume waveguide. To reduce sidelobe levels, the side slots may be elliptical.

Description

Technical Field

[0001] The technical field relates generally to antennas and, more particularly, to cavity-backed slot array antenna systems that provide reduced sidelobe losses and improved bandwidth in sub-terahertz applications such as radar imaging.

[0002] Generally, range, velocity, azimuth, and other target properties are measured by radar devices. In some applications, such as radar systems for vehicles, it may be desirable to provide information representing or relating to the characteristics of a target or object detected by the radar system. This information can be used to evaluate the detected target or object. In applications such as object detection and classification, the ability to quickly and accurately identify approaching objects is required. The azimuth and elevation of an object are typical parameters of interest. Receiving accurate object information for processing requires an antenna that supports the identification requirements, including by operating reliably over a sufficiently wide frequency bandwidth.

[0003] Antennas radiate energy in a pattern, and any lobes of radiation in that pattern that extend in directions other than the intended coverage direction are called side lobes. The sidelobe level (SLL) refers to the relationship between the side lobes and the main lobe of the radiation pattern. A large SLL may result in receiving less than optimal information about the target or may interfere with accurate target identification. Therefore, a low SLL is desirable because it means minimal power is radiated in unwanted directions and maximum power is radiated in the intended coverage direction.

[0004] Waveguide slot antennas are antennas used for high-frequency and high-power applications. Waveguide slot antennas are typically fed by a closed waveguide that serves as a wave transmission carrier to feed the slot. However, the closed waveguide with different levels of radiation and grounding elements requires a considerable amount of space to transmit the waves to the slot. In addition, slot antennas can be complex to manufacture and have relatively high manufacturing and assembly costs. Printed antennas with coplanar waveguides have advantages such as small form factor, light weight, small size, use of thin coplanar feeding and grounding elements, and small footprint. However, one of the limitations of antennas fed by coplanar waveguides is that their radiation is not directional enough. In addition, managing the SLL in array printed antennas is challenging.

[0005] Electromagnetic wave propagation in a waveguide is characterized by having a variety of waveforms. One form is the transverse electric (TE) mode, a waveguide mode that relies on transverse waves, in which the wave's electric vector is perpendicular to the direction of propagation. Another form is the transverse magnetic (TM) mode, in which the wave's magnetic vector is perpendicular to the wave's direction of propagation. A third form is the transverse electromagnetic (TEM) mode, in which both the wave's electric and magnetic vectors are perpendicular to the direction of propagation. Yet another form is the quasi-transverse electromagnetic (quasi-TEM) mode, characterized by waves with propagation-axis oriented components of both the electric and magnetic vectors. A given waveguide typically has only one dominant mode. Thus, a closed or coplanar waveguide will have only one of the TE, TM, or TEM modes as its dominant mode.

[0006] Therefore, it is desirable to provide an antenna system that provides desirable performance characteristics, such as improved SLL, greater bandwidth, and wider operating modes. Moreover, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. Summary of the Invention

[0007] The antenna system operates in a hybrid coplanar waveguide and rectangular waveguide mode. In various embodiments, a slot array having a conductive layer is disposed on a substrate and defines a coplanar waveguide that connects a plurality of side slots arranged in a row to form a slot array. Another substrate is spaced apart from the substrate and defines a ground plane thereon. A defined volume waveguide is disposed between the substrates. The system is configured to radiate a radiation pattern in a hybrid mode that is a combination of the slot array and the defined volume waveguide. To improve sidelobe level reduction, the side slots can be elliptical.

[0008] In further embodiments, a plurality of conductive posts ground the conductive layer to a ground plane and define the defined volume waveguide together with the conductive layer and the ground plane.

[0009] In further embodiments, the defined volume waveguide is rectangular.

[0010] In further embodiments, each of the plurality of side grooves is oval.

[0011] In further embodiments, the elliptical shape of the side grooves is elongated in a direction perpendicular to the coplanar waveguide.

[0012] In further embodiments, signal coupling is provided between the coplanar waveguide and the defined volume waveguide.

[0013] In another embodiment, the coplanar waveguide is configured in a quasi-TEM mode, and the confined volume waveguide is configured in a TE mode. The radiation pattern is generated by a mixed mode of the quasi-TEM mode and the TE mode.

[0014] In further embodiments, a transceiver module is disposed between the substrates and coupled to the coplanar waveguide and the defined volume waveguide.

[0015] In further embodiments, one of the substrates is a radio frequency printed circuit board, and the ground plane is disposed on the radio frequency printed circuit board.

[0016] In another embodiment, the radar processing module is disposed on a radio frequency printed circuit board and is coupled to the coplanar waveguide and the defined volume waveguide through the transceiver module.

[0017] In various additional embodiments, an antenna system includes a slot array defined by a conductive layer disposed on a substrate. The conductive layer defines a coplanar waveguide that connects a plurality of side slots arranged in a row to form the slot array. The side slots are spaced apart from each other and each has an elliptical shape. A ground plane is defined on another substrate, the other substrate being spaced apart from the substrate on which the slot array is disposed. A defined volume waveguide is disposed between the two substrates. The system is configured to radiate a radiation pattern in a hybrid mode generated by the combination of the slot array and the defined volume waveguide.

[0018] In further embodiments, a plurality of conductive posts ground the conductive layer to a ground plane and define the defined volume waveguide together with the conductive layer and the ground plane.

[0019] In another embodiment, the elliptical shape of the side groove is elongated in a direction perpendicular to the coplanar waveguide.

[0020] In another embodiment, a transition portion is provided between each side slot and the coplanar waveguide, wherein the transition portion is arranged near an end of the ellipse.

[0021] In further embodiments, signal coupling is provided between the coplanar waveguide and the defined volume waveguide.

[0022] In another embodiment, the coplanar waveguide is configured in a quasi-TEM mode, and the confined volume waveguide is configured in a TE mode.The radiation pattern is generated by a hybrid mode that is a combination of the quasi-TE mode and the TE mode.

[0023] In further embodiments, a transceiver module is disposed between the substrates and coupled to the coplanar waveguide and the defined volume waveguide.

[0024] In further embodiments, one of the substrates is a radio frequency printed circuit board, and the ground plane is disposed on the radio frequency printed circuit board.

[0025] In another embodiment, the radar processing module is disposed on a radio frequency printed circuit board and is coupled to the coplanar waveguide and the defined volume waveguide through the transceiver module.

[0026] In many other embodiments, an antenna system includes a substrate made of a dielectric material. A conductive layer on the substrate defines a feed slot connecting a plurality of side slots arranged in a row to form an antenna array in the conductive layer. The side slots are spaced apart from each other, and the array is disposed on the first substrate. The side slots are elliptical in shape. A coplanar waveguide is configured to transmit signals to the antenna array. A radio frequency printed circuit board substrate is spaced apart from the dielectric substrate. A ground plane is disposed on the radio frequency printed circuit board substrate. A plurality of conductive posts ground the conductive layer to the ground plane. The conductive layer, the ground plane, and the conductive posts define a confined volume waveguide. The system is configured to generate a radiation pattern of electromagnetic energy from the antenna array and the confined volume waveguide. The coplanar waveguide is configured for a quasi-TEM mode, while the confined volume waveguide is configured for a TE mode, and the radiation pattern generates a hybrid mode that is a combination of the quasi-TEM mode and the TE mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Exemplary embodiments will be described below with reference to the following drawings, wherein like reference numerals represent like elements, and wherein:

[0028] Figure 1 is a functional block diagram of an antenna system according to one embodiment;

[0029] Figure 2 is a schematic diagram of azimuthal coverage of an antenna system in a vehicle according to one embodiment;

[0030] Figure 3 is a schematic diagram of elevation coverage of an antenna system in a vehicle according to one embodiment;

[0031] Figure 4 According to one embodiment Figure 1 Schematic detailed illustration of a part of the antenna system

[0032] Figure 5 According to one embodiment Figure 1 A schematic plan view of a portion of an antenna system;

[0033] Figure 6 According to one embodiment Figure 5 a schematic side view of an antenna system; and

[0034] Figure 7 yes Figure 4 Far-field comparison of the antenna system with elliptical slots and the antenna system with non-elliptical slots. DETAILED DESCRIPTION

[0035] The following detailed description is merely exemplary in nature and is not intended to limit application and use. In addition, it is not intended to be bound by any theory, expressed or implied, presented in the preceding technical field, background technology, summary of the invention, or the following detailed description. As used herein, the term module refers to a dedicated integrated circuit, an electronic circuit, a processor (shared, dedicated, or grouped) and a memory that executes one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the functionality.

[0036] This specification discloses configurations and implementations of antenna systems for operating at very high frequencies (e.g., 228-240 GHz, in the sub-terahertz frequency range used for applications such as radar imaging). Embodiments of the antenna architectures and components disclosed herein can typically utilize a thin interposer substrate of dielectric material (e.g., silicon) that supports a hybrid antenna configuration in a small package. In many embodiments, the antenna system efficiently radiates electromagnetic energy for a radiation pattern with beneficial coverage and low SLL. The antenna radiating structure typically includes an array of slotted layers and a defined volume waveguide. The defined volume waveguide can be rectangular and can be defined by a slotted layer, a plurality of conductive posts, and a ground plane. The ground plane can be located on a radio frequency printed circuit board (RF-PCB), which can contain additional integrated circuits and electronic components. Feed lines connect the transceiver (Tx, Rx chip) directly to the antenna to send and receive inputs / outputs from the radio frequency integrated circuit. The transition from the coplanar waveguide to the slotted array is used to excite the array and provides signal coupling between the coplanar waveguide and the rectangular waveguide for dual excitation. The design of the hybrid radiating system advantageously produces a high-power radiated signal. The elongated nature of the system produces a relatively narrow beamwidth in elevation and a relatively wide beamwidth in azimuth. In many embodiments, multiple antennas, such as three or four, can be arranged in azimuth to provide narrow beams and beam scanning capabilities. Providing multiple antennas, each with a narrow beam, provides better scanning resolution. In other applications, the antennas can be customized to have different beamwidths corresponding to the field of view of interest. In many embodiments, the antenna system provides low SLL over a 12 GHz bandwidth and provides a desired radiation pattern in a compact, low-cost architecture.

[0037] refer to Figure 1, a functional block diagram of an antenna system 100 for radar applications includes a transceiver module 102 that provides transmit (Tx) and receive (Rx) functionality. The transceiver module 102 is coupled to a cavity-backed slot array (CBSA) antenna module 104, which includes a transmit / receive antenna structure having a coplanar waveguide 106 and a defined volume waveguide 108 in the form of a rectangular waveguide. Signal coupling 110 is provided between the coplanar waveguide 106 and the waveguide 108, and radiation occurs in a mixed-mode configuration. According to features further described below, the antenna module 104 is configured to radiate 112 and receive 114 electromagnetic energy. In transmission, the antenna module 104 receives a signal from the transceiver module 102 and radiates 112 a radio frequency signal. In reception 114, the antenna module 104 detects any reflections from potential targets and passes the signal to the transceiver module 102. In the current embodiment, the transceiver module 102 is directly coupled to the antenna module 104.

[0038] Radar processing module 116 interfaces with transceiver module 102 via physical signal coupling 118, as described further below. In some embodiments, the processor and transceiver functionality can be on the same chip. In the current embodiment, processing module 116 includes a processor that sends control signals to transceiver module 102, processes received signals to identify targets and their attributes, and can act as an interface with other controllers (such as the vehicle's electronic control unit) via vehicle interface physical layer 119. For example, processing module 116 can receive data about reflections, compare them with the transmitted signal, and determine the target's range, angle, and velocity. In the current embodiment, transceiver module 102 is a single-chip, standalone frequency-modulated continuous wave (FMCW) transceiver solution for the desired GHz frequency band. Other embodiments may utilize separate transmitter and receiver devices. In the current embodiment, transceiver module 102 contains circuitry, including a power amplifier, low-noise amplifier, phase shifters, switches, filters, DC bias, etc., for operating and connecting to antenna module 104. The transceiver module 102 may communicate communication data to and from the radar processing module 116, from which the data is in turn communicated to and from the antenna module 104. In the current embodiment, the transceiver module 102 is contained on a single chip and may be implemented as a monolithic microwave integrated circuit (MMIC) chip.

[0039] refer to Figure 2 and 3, the antenna system 100 can be applied to a vehicle 120 to cover a specific area, in this example, the area in front of the vehicle 120. It should be understood that additional antennas and / or antenna systems can be included to, for example, provide radars with different ranges, such as long range and medium range. Additional radars can be used to detect targets in multiple directions, such as to the side of the vehicle 120 and / or to the rear of the vehicle 120. The radar radiation can be three-dimensional, but for the purposes of this disclosure, it is represented by horizontal (azimuth) and vertical (elevation) radiation patterns.

[0040] The radiation pattern of antenna system 100 depends on the structure of antenna module 104 , as described further below, and its mounting, in this example on vehicle 120 . Figure 2 The radar's beamwidth 122 is depicted in an azimuth plane 124, assuming the radar is at the front bumper of a vehicle 120. In some embodiments, multiple antennas, such as three or four, can be arrayed, and the beamwidth can be tailored to cover road lanes 126 with a viewing angle 123 of approximately ±15 degrees, or a total of 30 degrees, while avoiding detection of vehicles in adjacent lanes 130. In other embodiments, the field of view is selected for the application. Figure 3 The beamwidth 132 of the radar is depicted in a vertical plane 134. In the vertical plane 134, the coverage may be narrower, such as ±5 degrees or a total of 10 degrees.

[0041] refer to Figure 4The structure of antenna system 100 is schematically shown in cross-section. Antenna system 100 includes integrated components connected to a radar integrated circuit, including a radar processing module 116 located on a radio frequency printed circuit board (RF-PCB) 140. An interposer component 142 is mounted on RF-PCB 140 via conductive posts, which in this embodiment are copper posts 144. The copper posts extend from an interposer substrate 146 to conductors on RF-PCB 140. In this embodiment, the conductors include a ground plane 148 and conductive patches 150, and interposer substrate 146 comprises a dielectric, particularly silicon. RF-PCB 140 has a metal layer printed or otherwise deposited or applied to a surface 152 of substrate 156. This metal layer serves as a conductor, including ground plane 148 and conductive patches 150, which provide connections between radar processing module 116 and transceiver module 102 / antenna module 104. Copper pillars 144 support and ground interposer 146 at a location spaced apart from ground plane 148 of RF-PCB 140. Surface 154 of interposer 146 is free of any additional layers above the silicon and, in this embodiment, contains no electronic components that would otherwise need to be coupled through interposer 146, thereby limiting complexity. An array antenna layer 158 is defined by a conductive material and is disposed on surface 160 of interposer 146 facing ground plane 148. Array antenna layer 158 includes coplanar waveguides 106. The need for any structure passing through interposer 146 (which would otherwise be used to couple to electronic components at surface 154) is avoided because it is clear.

[0042] On a surface 160 of the interposer substrate 146 that faces the ground plane 148, a redistribution layer 162 includes a conductive material 164, such as a metal, in this embodiment copper, that is printed or otherwise applied to the surface 160. The redistribution layer 162 provides a transition from the transceiver module 102 to the conductive feed for the CBSA antenna module 104.

[0043] The transceiver module 102 is connected to, and in particular from, the redistribution layer 162 via transitions 166, 168. Transitions 166, 168 provide low-loss feed transmission from the transceiver module 102 to the antenna module 104 for efficient excitation. The structure of the antenna system 100 illustrates that the feed is connected through the transceiver module 102, which is effectively located between the substrate 156 and the interposer substrate 146 of the RF-PCB 140. The antenna feed can be located on the same surface 160 of the interposer substrate 146 as the transceiver module 102 and the array antenna layer 158. Consequently, the illustrated embodiment is advantageous from a cost and manufacturing complexity perspective.

[0044] An air cavity in the form of a waveguide 108 is formed between the interposer substrate 146 and the RF-PCB substrate 156. Specifically, the waveguide 108 has a volume defined and bounded by the array antenna layer 158, the ground plane 148, and the copper pillars 144. Thus, the shape of the waveguide 108 is rectangular. In other embodiments, other shapes of the waveguide 108 may be used.

[0045] Processing module 116 communicates via RF-PCB 140, and interposer assembly 142 includes an interposer substrate 146 and transceiver module 102, with appropriate transmission line connections. Antenna system 100 enables transmit signals from processing module 116 to be connected to antenna module 104 via transceiver module 102. In reception, antenna module 104 collects incoming signals, which are sent by transceiver module 102 to processing module 116. When coupled with an antenna having the geometry described below, this configuration provides a compact package and desirable RF performance at applicable operating frequencies. It will be appreciated that the operating frequency of the antenna system can be over a bandwidth such as 12 GHz, for example, 228-240 GHz.

[0046] The components of the antenna system 100 are Figure 5 and 6 108, specifically showing details of the array antenna layer 158 and the waveguide 108. The antenna array 170 is a slot array and is defined in the array antenna layer 158. The antenna array 170 includes a conductive layer 172, which in this embodiment is a copper material, provided on the entire or substantially the entire surface of the substrate 174. The conductive layer can be connected to Figure 4 The antenna array 170 is configured as a traveling wave array for wide bandwidth and low loss. The antenna array 170 includes a plurality of side slots 176 fed by the coplanar waveguide 106. Two feeding slots 178, 180 of the coplanar waveguide 106 are formed completely through the thickness of the conductive layer 172 and extend a length from the feeding end 182 to the opposite end 184 and are connected together at the end 184. The feeding slots 178, 180 are parallel to each other and are defined on opposite sides of the conductive signal line 186 and are defined on a gap 188 of 120 μm.

[0047] Feed slots 178, 180 are connected to several side slots 176, which are arranged in pairs along antenna array 170, in this case, eight pairs of 16 slots. In other embodiments, a different number of side slots 176 can be used to achieve the desired coverage and resolution. For example, adding additional pairs of side slots along the length of antenna array 170 can increase resolution. The radiating elements of antenna array 170 are side slots 176, each directly coupled to one of the feed slots 178, 180 to receive the propagating waves. The side slots 176 radiate individually, and due to their array configuration, the radiation from all elements is combined to form the antenna array's radiation beam, which has high gain and high directivity with minimal losses. Antenna performance is a function of the configuration of antenna array 170. In the current embodiment, the side slots 176 are elliptical, with their long dimension extending transversely at 90 degrees relative to the feed slots 178, 180, which has been found to be beneficial for reducing SLL. The transition 191 between the side slots 176 and the feed slots 178, 180 is defined near the narrow end 193 of the elliptical shape, opposite the elongated side 195 of the elliptical shape for active signal feeding. The side slots 176 have a uniform spacing 190 of 555 μm, and each pair of aligned side slots 176 has a length 192 of 641 μm and a width 194 of 140 μm for optimal performance in the 228-240 GHz range.

[0048] like Figure 6 As shown, copper pillars 144 extend from the conductive layer 172 to the ground plane 148. A cavity 196 of the waveguide 108 is disposed between the conductive layer 172 and the ground plane 148 and is defined by the copper pillars 144. The copper pillars 144 surround the antenna array 170 and have a height such that the height 198 of the waveguide 108 is defined as 75 μm. The copper pillars 144 are positioned with a width 200 of 641 μm, which is consistent with the slot length 192 to reduce wave leakage. The coplanar waveguide 106 and the waveguide 108 are coupled to the transceiver module via a ground-signal-ground feed at a coplanar waveguide transition 202.

[0049] The combination of elliptical side slots 176, coplanar waveguide 106, and waveguide 108 provides an efficient, low-SLL, strong radiation pattern, sub-THz CBSA antenna. The elliptical shape of the side slots 176 supports a beneficial radiation pattern that, when coupled with radiation from the signal coupling waveguide 108, produces an electric field radiation pattern at the array antenna layer 158 that extends substantially laterally across the 641 μm distance of the side slot length 192 and the column width 200. By using elliptical side slots 176, hybrid transmission modes are enhanced, significantly improving SLL compared to non-elliptical slots. The coplanar waveguide transition 202 connects to the transceiver module 102 and is the primary transmission line for signal flow. The waveguide 108 prevents backside radiation, and its transmission mode combines with the coplanar waveguide mode to form a hybrid mode that also improves SLL. At 240 GHz, the CBSA antenna module has been found to improve overall SLL by 33%. Figure 7 An example reduction is shown in FIG, where approximately 30 degrees of effective coverage with reduced SLL is shown by curve 210 compared to curve 212. The solid line of curve 210 is for the antenna system 100 with the elliptical side slots 176, while the dashed line of curve 212 is for the antenna system without the elliptical side slots (corner side slots 216) and without signal coupling between the coplanar waveguide and the rectangular waveguide. In particular, the side lobes 214 are significantly reduced, which improves detection accuracy. By using the elliptical side slots 176 and the antenna array 170 supported by the waveguide 108, a hybrid transmission mode is delivered, which is a combination of the quasi-TEM mode from the coplanar waveguide 106 and the TE transmission mode from the waveguide 108. The hybrid mode improves the SLL at the higher frequency edges, thereby increasing the bandwidth.

[0050] According to the embodiments described herein, an antenna configuration operating in the 228-240 GHz frequency range is provided for applications including radar imaging. The antenna system utilizes coplanar waveguide-fed slot radiators and rectangular waveguide radiators in a hybrid arrangement. This configuration provides desirable performance characteristics and simplifies manufacturing and assembly. These embodiments can be used to cover multiple areas, such as the perimeter of a vehicle. The feed transitions connect relatively directly to the transmit and receive elements. It has been discovered that the design of the radiating element with an elliptical slot results in an unexpectedly strong radiation pattern and reduced SLL.

[0051] Although at least one exemplary embodiment has been given in the foregoing detailed description, it should be understood that there are a large number of variations. It should also be understood that one or more exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. On the contrary, the foregoing detailed description will provide those skilled in the art with a convenient roadmap for implementing one or more exemplary embodiments. It should be understood that various changes may be made to the function and arrangement of elements without departing from the scope of the present disclosure as set forth in the appended claims and their legal equivalents.

Claims

1. An antenna system comprising: a first substrate; a slot array defined by a conductive layer disposed on the first substrate, wherein a coplanar waveguide connects a plurality of side slots arranged in a row to form the slot array; a second substrate spaced apart from the first substrate; a ground plane defined on the second substrate; and a confined volume waveguide disposed between the first substrate and the second substrate, wherein the coplanar waveguide extends along the first substrate parallel to the confined volume waveguide, the slot array and the confined volume waveguide each substantially fill an area of ​​substantially the same size surrounding the first substrate, Wherein the system is configured to radiate a radiation pattern in a hybrid mode from a combination of the slot array and the defined volume waveguide. 2 . The system of claim 1 , comprising a plurality of conductive posts grounding the conductive layer to the ground plane and defining the defined volume waveguide together with the conductive layer and the ground plane.

3. The system of claim 2, wherein the defined volume waveguide is rectangular.

4. The system of claim 1, wherein each of the plurality of side grooves is oval in shape.

5. The system according to claim 4, wherein: The elliptical shape of the side groove is elongated in a direction perpendicular to the coplanar waveguide.

6. The system of claim 1 , comprising signal coupling between the coplanar waveguide and the defined volume waveguide.

7. The system of claim 1 , wherein the coplanar waveguide is configured for a quasi-transverse electromagnetic (quasi-TEM) mode and the confined volume waveguide is configured for a transverse electric (TE) mode, and the radiation pattern is produced by the hybrid mode, which is a combination of the quasi-transverse electromagnetic mode and the transverse electric mode.

8. The system of claim 1, comprising a transceiver module disposed between the first substrate and the second substrate, the transceiver module coupled to the coplanar waveguide and to the defined volume waveguide.

9. The system of claim 8, wherein the second substrate comprises a radio frequency printed circuit board, wherein the ground plane is disposed on the radio frequency printed circuit board.

10. The system of claim 9, comprising a radar processing module disposed on the radio frequency printed circuit board, the radar processing module being coupled to the coplanar waveguide and the defined volume waveguide through the transceiver module.

Images