CN113725601B - A multi-field array antenna for millimeter wave automotive radar - Google Patents

Abstract

The invention discloses a multi-view field array antenna for a millimeter wave automobile radar, which consists of three layers of dielectric materials and four layers of metals, wherein the metal layers comprise a radiation layer, an antenna reflection layer, a strip line feed layer and a bottom floor layer. The radiation layer is etched with an array formed by four or more combined antennas, and the antennas are formed by two radiation units of grid units and patch units. Each antenna is symmetrical about the central line of the array, each antenna is composed of more than two identical grid radiating units which are equidistantly arranged, the non-radiating side of each grid unit replaces the traditional straight line by a bending arc, and the radiating side replaces the traditional microstrip line with the same width by a gradual change microstrip line. And patch units are added in a blank area in the middle of the grid unit, and a series patch antenna is formed by the patch units and the connection sections between the patch units, so that the antenna area is effectively utilized. Through carrying out wave beam shaping design on the array, the directional diagram is provided with a plurality of 'flat shoulder' shaped characteristics, and different view fields divided by the 'flat shoulder' meet the detection requirements of the radar on targets in different distance ranges. The invention has simple structure, can realize the integration of multiple detection distance functions of the radar by only one transmitting chain, reduces the processing difficulty of front-end signals, and is suitable for millimeter wave band automobile radars.

Description

A multi-field array antenna for millimeter wave automotive radar

Technical field

The patent of this invention relates to wireless communication equipment, especially to vehicle radar antennas. Specifically, it is a multi-field array antenna for millimeter wave automotive radar designed using planar technology.

Background technique

With the development of smart cars and driverless technology, automotive radar is increasingly becoming an indispensable and important part of cars. Compared with radars based on ultrasonic, infrared, and laser systems, millimeter-wave automotive radar has the characteristics of large bandwidth, high resolution, small size, low cost, and can work in any harsh weather environment. At present, in millimeter-wave automotive radar, in order to achieve target detection and early warning in different ranges, more than one transmitting array antenna is generally required. For example, in order to detect large targets at long distances, the array size needs to be large enough to achieve high-gain narrow beams; in order to detect small targets at close range, a single linear array is often used to achieve low-gain wide beams. Multiple transmit arrays are activated in a time-shared working state through the front-end radio frequency chip. On the one hand, the number of chip links is required, resulting in redundant transceiver link resources. On the other hand, it also increases the difficulty of front-end signal processing.

Summary of the invention

The purpose of the patent of this invention is to overcome the shortcomings of the existing technology and provide a multi-field array antenna for millimeter wave automotive radar. The array is composed of miniaturized combined antennas and includes two forms of radiation: grid units and patch units. unit. Among them, by bending the non-radiating edge into an arc shape, the size of the grid antenna is reduced, meeting the requirements of the general array design array spacing of 0.5λ ₀ (λ ₀ is the air wavelength), and avoiding the traditional grid antenna due to the radiation edge Excessive spacing causes grating lobes in array design. A patch unit is added to the blank area in the middle of the grid unit and connected with the connecting section between the grid units to form a series patch antenna, which effectively utilizes the antenna area. The two radiating units produce two resonant mode radiations with different frequencies to achieve bandwidth expansion. . The array pattern is filled with zero points through the beamforming design, achieving radar-free detection within a range of ±60°. The pattern has a "flat shoulder" feature, and the multiple fields of view thus divided can meet the needs of the radar. Detection requirements for targets of different ranges and sizes.

The antenna provided by the patent of the present invention is characterized by being composed of three layers of dielectric materials and four layers of metal. The metal layers include the radiating layer, the antenna reflecting layer, the stripline feed layer and the bottom floor layer. The radiation layer is etched with an array composed of four or more combined antennas, and each combined antenna is symmetrical about the center line of the array. According to the number of array elements and the number of required multiple fields of view, through the array beamforming design, the specific array spacing, feed amplitude and phase distribution can be obtained to make the pattern have a "flat shoulder" characteristic.

The antenna provided by the patent of the present invention is characterized in that the combined antenna is composed of two types of radiating units: grid units and patch units. It includes two or more identical grid radiating units arranged at equal distances. By combining the grid units The non-radiating edges are replaced by curved arcs from traditional straight lines, and the spacing between the radiating edges is reduced to less than 0.3λ ₀ (λ ₀ is the wavelength of air), which reduces the size of the antenna and meets the requirement of an array spacing of 0.5λ ₀ in general array design. , avoiding the problem of grating lobes in array design caused by traditional grid antennas due to excessive radiation edge spacing. The radiating edge is replaced by a gradient microstrip line for the traditional same-width microstrip line. The minimum line width is consistent with the non-radiating edge line width, ensuring the continuity of the microstrip line at the connection between the radiating edge and the non-radiating edge. By adjusting the maximum line width, the Used to improve matching and radiation performance. The connecting section between units also has a radiating effect, so the length and width are consistent with the radiating edge. A patch unit is added to the blank area in the middle of the grid unit, and is connected to the non-radiating edge of the grid through a microstrip line. It forms a series patch antenna with the connecting section between units, effectively utilizing the antenna area. Since the area in the middle of the grid unit is smaller, the resonant mode frequency generated by the patch antenna is slightly higher than that of the grid antenna. Therefore, the two forms of radiating units form a combined antenna effect, in which the patch unit generates high-frequency resonant mode radiation, and the mesh antenna The grid unit generates low-frequency resonant mode radiation, and the two generated resonant mode radiations broaden the antenna operating bandwidth. The slotted patch unit connected in series at the end of the antenna acts as a matching load to improve the matching performance. The stripline feed layer uses vias to feed the top radiating layer, and the feed position is symmetrical about the center of the line array to achieve differential feed. The via hole passes through the through hole on the antenna reflection layer and is connected to the strip line feed layer. Near the connection point between the via hole and the strip line feed layer, there is an equivalent electrical wall composed of a ground via hole; the strip line feed layer The electrical layer contains a multi-stage T-shaped power division phase-shifting network. Each stage of the power division phase-shifting network relies on the output port line width to achieve amplitude distribution, and relies on the additional length to achieve phase distribution. The multi-stage power division phase-shifting network ensures that the array element amplitude and phase are distributed according to the shaping calculation values, thereby achieving beam forming.

The characteristic of the antenna provided by the patent of this invention is that the differential feed ensures that the current direction of the radiating edge of the grid is the same and the current direction of the non-radiating edge is opposite. The via hole is located at the intersection of the non-radiating edge of the grid and the connection section between units and is related to the combination. The antenna is symmetrical about the center.

The antenna provided by the patent of the present invention is characterized in that an equivalent electric wall formed by a grounding hole is provided near the connection between the via and the stripline feeding layer to reduce the energy loss during layer change transmission. Adjusting the size of the grounding hole and the spacing between the grounding vias can improve the matching degree of the layer change transition structure.

The antenna provided by the patent of the present invention is characterized by a T-shaped power division structure at each stage, including a quarter-wavelength line segment and a cut angle to improve port matching.

The antenna provided by the patent of the present invention is characterized in that the T-shaped power division structure input strip line matches the chip output. Its end can be connected to the feeder lead from the chip pin through a layer-changing transition structure.

The antenna provided by the patent of the present invention is characterized in that the overall structure can be realized by low-temperature co-fired ceramic technology or multi-layer printed circuit board technology.

Compared with the prior art, the advantages of the present invention are:

1. Through beamforming design, the array pattern has multiple "flat shoulders" features at ±60°

There are no zero points in the range, and the beam coverage has no blind spots. Multiple fields of view divided by "flat shoulders" can meet the radar's needs to detect targets in different ranges at the same time. The function that originally required multiple arrays of different sizes to work in time-sharing can be achieved through a beamforming array fed by a single link, which greatly reduces the antenna's demand for the number of transceiver chip links and the difficulty of signal processing.

2. The distance between the radiation edges of the miniaturized grid antenna is shortened to less than 0.3λ ₀ (λ ₀ is the wavelength of air), meeting the 0.5λ ₀ array element spacing requirement in general array design, avoiding the grating lobe problem that occurs in the array design of the traditional grid array due to the large size of the H surface. Compared with the traditional grid antenna with the same number of array elements, the beam width is wider and more suitable for radar to detect large-scale targets.

3. Add a patch unit to the blank area in the middle of the grid unit to form a series patch antenna. The two units are used to generate resonant mode radiation of different frequencies to achieve bandwidth expansion, ensuring the stability of radar performance within a wide frequency band and effectively utilizing Antenna area.

Description of drawings

Figure 1 is a structural side cross-sectional view of a multi-field array antenna for millimeter wave automotive radar patented by the present invention.

Figure 2 is a top view of the radiation layer of a multi-field array antenna for millimeter-wave automotive radar patented by the present invention.

Figure 3 is a side view of the layer-changing transition structure of a multi-field-of-view array antenna for millimeter-wave automotive radar patented by the present invention.

Figure 4 is a top view of the feed layer of a multi-field-of-view array antenna for millimeter-wave automotive radar patented by the present invention.

Figure 5 is a pattern simulation result diagram of a multi-field-of-view array antenna for millimeter-wave automotive radar patented by the present invention.

Figure 6 is a diagram showing the impedance bandwidth simulation results of a multi-field-of-view array antenna for millimeter-wave automotive radar patented by the present invention.

Detailed ways

The patent of the present invention will be described in further detail below with reference to the embodiments and drawings. However, the scope of protection claimed by the patent of the present invention is not limited to the scope involved in the embodiments.

The antenna structure provided by the patent of the present invention is shown in Figure 1. The overall structure includes three layers of dielectric materials and four layers of metal. The metal layers include the radiating layer, the antenna reflecting layer, the stripline feed layer and the bottom floor layer. The top view of the radiation layer is as shown in Figure 2. An array composed of four or more combined antennas is etched. The array spacing d ₁ , d ₂ , d ₃ , d ₄ and the feed amplitude and feed phase are symmetrical about the array center line. According to the number of array elements and the number of required multiple fields of view, through the array beamforming design, the specific array spacing, feed amplitude and phase distribution can be obtained to make the pattern have a "flat shoulder" characteristic. The combined antenna is composed of radiating units in the form of grid units and patch units, including two or more identical grid radiating units arranged at equal distances. By replacing the non-radiating edges (11) of the grid units with traditional straight lines It forms a curved arc, and the radiating edge spacing is reduced to less than 0.3λ ₀ (λ ₀ is the air wavelength), which reduces the size of the antenna and meets the general array design requirement of an array spacing of 0.5λ ₀ and avoids the traditional grid antenna due to radiation Excessive edge spacing causes grating lobes problems during array design. The radiating edge is replaced by a gradient microstrip line for the traditional same-width microstrip line. The purpose is to reduce the mismatch caused by the discontinuity of the microstrip line at the connection between the radiating edge and the non-radiating edge. The connecting section between units has the same size as the radiating edge, which has the advantage of facilitating processing. A patch unit is added to the blank area in the middle of the grid unit, and is connected to the non-radiating edge of the grid through a microstrip line, and forms a series patch antenna with the connecting section between units to improve the antenna area utilization. Since the radiation principle of both forms of radiating units is slot radiation, and the middle area of the grid is small, the operating frequency of the patch unit will be slightly higher than that of the grid unit, so the two forms of radiating units form a combined antenna effect. By adjusting the operating frequency of the unit, the two sets of resonant mode radiation generated broaden the antenna operating bandwidth. In this embodiment, the low-frequency resonance mode radiation frequency generated by the grid unit is 78 GHz, and the high-frequency resonance mode radiation frequency generated by the patch unit is 83 GHz.

The antenna uses via feeding, and the feeding point position is symmetrical about the center of the linear array to meet the symmetry of the radiation pattern. It is generally selected at the intersection of the non-radiating edge of the grid and the connecting section between the units. The via passes through the through hole on the antenna reflective layer and is connected to the stripline feeding layer, where the via and the through hole form a 50Ω coaxial line filled with dielectric material. The stripline feeder layer is described in Figure 3. Near the connection between the via and the feeder layer, there is an equivalent electric wall formed by a grounding hole. By adjusting the size of the grounding hole and the spacing of the grounding vias, the loss and mismatch of energy during layer-changing transmission can be reduced. The power division phase shift feeding network includes a multi-stage T-shaped power division phase shift structure, as shown in Figure 4. Each stage of the power division phase shift structure relies on the output port line width to achieve amplitude distribution and relies on additional length to achieve phase distribution. The multi-stage power division structure ensures that the array element amplitude and phase are distributed according to the beamforming calculation value, thereby realizing beamforming. The shortest power division path is used to reduce the parasitic loss of the power division phase shift feeding network, improve the matching characteristics, and ensure the beamforming effect. The input part of the power division phase-shift feeding network is a 50Ω stripline, and the signal line led out from the front-end chip can be connected through a layer-changing transition structure. Therefore, unlike the circuit board technology used in general vehicle-mounted radar antennas, the antenna and chip are designed and packaged as one, making it possible to expand into a packaged antenna.

An example of applying the present antenna: For the sake of generality, all dimensions of this example are normalized to electrical length for the dielectric wavelength λ _g of the antenna center frequency 79 GHz, and the calculation of the array spacing and the amplitude phase distribution of each array element is not included in the embodiment. As shown in FIG2 , the array is composed of eight combined antennas and is symmetrical about the array center line 10, d ₁ , d ₂ , d ₃ and d ₄ are 1.61λ _g , 1.1λ _g , 1.03λ _g and λ _g respectively. Each combined antenna is composed of six grid units of the same size, wherein the grid non-radiating edge 11 is composed of four semicircular arcs, the arc impedance is 75Ω, the radius is 0.08λ _g , the total length of the stretch is λ _g , and the radiating edge spacing is reduced from 1.16λ _g to less than 0.68λ _g (0.28λ ₀ ); the characteristic impedance corresponding to the maximum width of the radiating edge 12 is 55.4Ω, the length is 0.64λ _g , and the size of the connecting section between two adjacent units is consistent with the length and width of the radiating edge. The length and width of the patch unit 14 in the middle of the grid are 0.26λ _g and 0.16λ _g respectively, and the length and width of the absorption load patch 15 loaded at the end are 0.32λ _g and 0.21λ _g respectively. As shown in Figure 3, the distance between the via hole and the center of the linear array is 2.9λ _g , and the via hole 6 and the antenna reflection stratum through hole 7 form a 50Ω coaxial line filled with dielectric material. As shown in Figure 4, the grounding hole 8 takes the position of the via hole 6 as the center of the circle and has a radius of 0.21λ _g to form an equivalent electrical wall. The power division phase shift feeding network includes a total of four power division phase shift structures, all of which are T-type equal power dividers, and the output port phase difference is achieved by adding length, wherein the electrical length difference of the two power dividers 20 in the last stage is 0.08λ _g and 1.35λ _g from the inside to the outside, respectively, and the electrical length difference of the second to last power divider 19 is 0.135λ _g . The electrical length difference of the first-stage power divider 17 is 0.5λ _g , and its function is to divide the energy of the input port into two equal and opposite parts to realize differential feeding. At this time, the two middle array elements are taken as the zero phase point, and the amplitudes of the array elements from the outside to the inside are equal, and the phase distribution is 75°, 25°, 10°, and 0°. The overall structure is realized by LTCC process, and the medium is FerroA6M-E ceramic material (ε _r =5.7±0.2, tanδ=0.002), the dielectric layer thickness is 96μm, and the metal layer thickness is 8μm.

Figure 5 shows the simulation results of the azimuth plane (the plane along the non-radiating edge of the grid and perpendicular to the structure) and the pitch plane (the plane along the radiating edge of the grid and perpendicular to the structure) pattern of this antenna. The results show that after the shaped design, the azimuth pattern of the array antenna has a double "flat shoulder" feature, which divides three fields of view into ±8°, ±21° and ±44° ranges, of which the maximum gain is 19dB. At this time, the field of view is the narrowest, which can detect large targets at long distances; the widest field of view is ±44°, and the gain is greater than 5dB, which can detect small targets at close range. The side lobe level in the elevation plane is lower than -14dB, the pattern has good symmetry, and there are no zero points within ±60° of the azimuth plane, so the radar can detect without blind spots.

Figure 6 shows the simulation results of the antenna impedance bandwidth of the patented design of the present invention. The results show that the antenna impedance bandwidth can fully cover the currently established millimeter wave 76–81GHz automotive radar frequency band.

As mentioned above, the patent of the present invention can be better realized. The patent of the present invention is not limited to the embodiments given above. Those skilled in the art can make different modifications under the concept of the present invention, such as using radiators of different shapes and sizes to replace the grid radiating edges and patches, thereby Obtain functional antennas such as wide impedance band and low side lobes; the antenna feed structure can be microstrip lines, substrate integrated waveguides, coplanar waveguides, etc.

Claims (5)

1. A multi-view field array antenna for millimeter wave automobile radar is characterized by comprising three layers of dielectric materials (1) and four layers of metals; the metal layer comprises a radiation layer (2), an antenna reflection layer (3), a strip line feed layer (4) and a bottom floor layer (5);

the radiation layer (2) is etched with an array formed by four or more combined antennas (9), and the combined antennas are symmetrical about an array center line (10); according to the number of array elements and the number of required multiple fields of view, specific array spacing, feed amplitude and phase distribution are obtained through the design of array beam forming, so that the directional diagram has a 'flat shoulder' characteristic;

the combined antenna (9) is composed of two types of radiation units, namely a grid unit and a patch unit, and comprises more than two identical grid radiation units which are equidistantly arranged, the distance between the radiation sides is reduced to be below 0.3λ0 by replacing the non-radiation sides (11) of the grid units with curved arcs from traditional straight lines, λ0 is the air wavelength, the size reduction of the antenna is realized, the requirement that the distance between the array design arrays is 0.5λ0 is met, and the problem that grating lobes appear in the array design of the traditional grid antenna due to overlarge distance between the radiation sides is avoided; the radiating edge (12) replaces the traditional microstrip line with the same width by the gradual change microstrip line, wherein the minimum linewidth is consistent with the linewidth of the non-radiating edge, the continuity of the microstrip line at the joint of the radiating edge and the non-radiating edge is ensured, and the matching and radiating performance is improved by adjusting the maximum linewidth; the inter-unit connection sections (13) also have a radiation effect, so that the length and the width are consistent with the radiation edges; a patch unit (14) is added in a blank area in the middle of the grid unit, and is connected with the non-radiation side of the grid through a microstrip line, and a series patch antenna is formed by the connection section between the patch units, so that the antenna area is effectively utilized; because the area in the middle of the grid unit is smaller, the resonant mode frequency generated by the patch antenna is slightly higher than that of the grid antenna, so that the two types of radiation units form a combined antenna effect, wherein the patch unit generates high-frequency resonant mode radiation, the grid unit generates low-frequency resonant mode radiation, and the two groups of resonant mode radiation generated widens the working bandwidth of the antenna; the slotted patch unit (15) connected with the tail ends of the antennas in series is used as a matching load to improve matching performance;

the strip line feed layer (4) feeds the top radiation layer (2) by adopting a via hole (6), and the position of the via hole (6) is positioned at the intersection point of the grid non-radiation side and the connecting section between the units and is bilaterally symmetrical relative to the linear array center (16) to realize differential feed; the via hole (6) passes through a through hole (7) on the antenna reflecting layer and is connected with the strip line feed layer (4), and an equivalent electric wall (8) formed by the grounding via hole is arranged near the connection part of the via hole (6) and the strip line feed layer (4) and is used for reducing the loss of energy during layer change transmission; the strip line feed layer comprises multi-stage T-shaped power division phase shifting structures (17), (18), (19) and (20), wherein each stage of power division phase shifting structure realizes amplitude distribution by means of line width of an output port and phase distribution by means of additional length; the multi-stage power division phase shift structure ensures that the amplitude and the phase of the array element are distributed according to the wave beam forming calculation value, thereby realizing wave beam forming.

2. A multi-field array antenna for a millimeter wave automotive radar as defined in claim 1 wherein the differential feed ensures that the grid radiating side currents are in the same direction and the non-radiating side currents are in opposite directions.

3. A multi-field array antenna for a millimeter wave automotive radar according to claim 1, characterized in that each stage of T-shaped power splitting structure comprises a quarter wavelength line segment (21) and a chamfer (22) for improving port matching.

4. A multi-field array antenna for a millimeter wave automotive radar according to claim 3, characterized in that the T-shaped power splitting structure input stripline (23) matches the chip output; the tail end of the chip is connected with a feeder line led out from a chip pin through a layer-changing transition structure.

5. The multi-field array antenna for a millimeter wave automobile radar according to claim 1, wherein the overall structure is realized by a low-temperature co-fired ceramic process or a multi-layer printed circuit board process.