Broadband dual circularly polarized microstrip-to-waveguide feed antenna system

Abstract

The present invention discloses an antenna system, including: a bridge, an upper metal ground, an upper substrate, a lower substrate, a lower metal ground, a radiation patch, a mode converter, a circular waveguide, and a metal via; the antenna system is a multi-layer board structure, which is an upper metal ground, an upper substrate, a lower substrate, and a lower metal ground from top to bottom; the radiation patch is located on the upper side of the upper substrate, and the mode converter is placed above the radiation patch and connected to the circular waveguide above it; the bridge constitutes a feeding network, and the two ports of the bridge are located between the upper substrate and the lower substrate. The feed antenna system of the present invention can achieve wideband and dual circular polarization in the millimeter wave frequency band, ensure that the transceiver port has good isolation, and realize the mode conversion of the microstrip antenna to the circular waveguide. The structure is simple and efficient, and the circular polarization performance is not changed. It can be used as a feed source for various types of antennas.

Description

Technical Field

[0001] The present invention relates to the field of antenna technology, and in particular to a wide-band dual circularly polarized 77 GHz microstrip-to-waveguide feed antenna system. Background Art

[0002] In the existing technology, millimeter wave radar technology has been widely used in the fields of automotive radar, security imaging, scene monitoring radar, level measurement, etc. The main advantages of millimeter wave radar technology are: high tracking accuracy and spatial resolution; high Doppler resolution and speed measurement accuracy; strong target recognition and imaging capabilities; good anti-interference ability.

[0003] Early radar technology was mainly based on pulse radar technology, but pulse radar technology has obvious disadvantages: for example, it requires a large transmission power, requires switching between transmission and reception, has a detection blind spot, is bulky, and is easily intercepted, etc. Continuous wave (CW) radar overcomes these disadvantages. It has the advantages of simple structure, small size, and low power, and is therefore increasingly widely used. Continuous wave radar can have a variety of modulation modes, among which frequency modulation continuous wave (FMCW) radar is the most widely used. Compared with pulse radar systems, FMCW radar has become increasingly valued due to its characteristics of no distance blind spot, high receiving sensitivity, strong anti-interference ability, high resolution, low power requirement, and simple structure. However, there are still many challenges in the technical development of continuous wave radar. First, since the frequency modulated continuous wave radar requires the transmit and receive (TX / RX) ends to work simultaneously, in order to keep the transmit and receive (TX / RX) ports from interfering with each other to obtain good working performance, there are higher requirements for the isolation of the transmit and receive ports between the transmit and receive (TX / RX) ports, which adds difficulty to the design of the back-end millimeter wave devices; secondly, the resolution of the frequency modulated continuous wave radar is determined by the bandwidth of the radar antenna. In order to ensure that the receiving port has high sensitivity and resolution, the receiving antenna needs to use a broadband antenna as much as possible, which brings challenges to the design of the transceiver antenna.

[0004] In the actual application of millimeter wave radar, such as the level measurement system, the antenna is required to have high gain and a small beam angle (3°), which can improve the link gain, increase the range and reduce interference. In this type of application scenario, lens antennas, horn antennas, reflector antennas, etc. become better choices, because in the 77GHz frequency band, the sizes of these antennas are usually small and can be actually processed and applied. At present, the core RF chips of millimeter wave radar systems are mostly monolithic microwave integrated circuits (Monolithic Microwave Integrated Circuit, referred to as MMIC), and their packaging form is mainly ball grid array (BGA) packaging. It can be seen that the RF system of the radar can be divided into a feed system with MMIC, feeder, and antenna as the core and a focusing system with lens / horn as the core. The design of the feeder and antenna after the transmit-receive (TX / RX) port of the RF chip is crucial. The primary challenge is how to convert the 77GHz band signal from the planar transmission line structure to the traditional waveguide structure or other three-dimensional structure, and further stimulate the lens or horn to achieve high-gain radiation; secondly, the wavelength of the 77GHz electromagnetic wave is only 3.9mm. Whether it is the printed circuit board (PCB) process or the computer numerical control (CNC) process, its processing accuracy has a great influence on the design of the antenna. How to design a highly robust antenna to adapt to the corresponding processing accuracy is another key point. In the millimeter wave frequency band frequency modulated continuous wave (FMCW) radar system, the main challenges faced by antenna design include: working bandwidth; transmit-receive end isolation; conversion from planar transmission line structure to transmit / receive structure; robust design.

[0005] See also Figure 1A-Figure 1D As shown, in the prior art, in order to achieve the isolation of transmission and reception, the antenna feeding network system generally adopts the following solutions: Figure 1A The 3dB bridge solution shown in Figure 1B The circulator scheme shown; Figure 1C The coupler scheme shown; Figure 1D The dual antenna solution shown.

[0006] However, the inventors have found through research that in the circulator solution, the properties of ferrite materials will change dramatically in the 77GHz frequency band, so it is difficult to implement using PCB technology. In the dual-antenna solution, one antenna is used for reception and one for transmission respectively; theoretically, as long as the two antennas are far enough apart, their isolation can be very good; but as a product design, two antennas will inevitably require double the space; especially in the 77GHz radar design, in order to achieve a longer communication distance, the size of the antenna is larger, and the two antennas will inevitably occupy a larger space, making the product structure more bloated. Therefore, in order to achieve transmission and reception isolation in the prior art, a circulator or dual antenna is used, wherein the circulator will cause antenna gain loss, and the dual antenna system will increase the size of the antenna, and due to its directivity problem, it will also cause antenna gain loss.

[0007] Since the receiving and transmitting ends of frequency modulated continuous wave (FMCW) radars work simultaneously, their antennas are mostly linearly polarized, resulting in poor isolation between the receiving and transmitting ports, which affects antenna performance. To solve this problem, a circulator can be added to improve the isolation between the receiving and transmitting ports, but the circulator will bring additional attenuation and reduce the sensitivity of the antenna; or, different antennas can be used for the receiving and transmitting ends, but this method will increase the size of the device and reduce the antenna gain due to directivity issues.

[0008] See also Figure 2 As shown, in the prior art, the microstrip to waveguide conversion scheme is often adopted. The circular waveguide has polarization degeneration due to its symmetry, which will excite various modes, and it is easier to excite high-order modes due to the discontinuity of the circular waveguide. Since the main mode TE10 mode of the rectangular waveguide is very similar to the main mode TE11 mode of the circular waveguide, through Figure 2 The rectangular-circular conversion structure shown can well realize mode conversion and reduce the generation of high-order modes, so it has good working performance; however Figure 2 The scheme shown destroys the circular symmetry and cannot generate circularly polarized waves. Referring to FIG3 , in the prior art, the depth of the short-circuit piston is often adjusted through microstrip probe excitation to perform impedance matching so that the energy coupled into the circular waveguide is maximized; however, the scheme in FIG3 requires the addition of a short-circuit piston, which brings certain difficulties to its processing design in the 77GHz millimeter wave frequency band, and because it directly converts from microstrip to circular waveguide, it is very easy to generate high-order modes, and its working bandwidth cannot meet the design requirements of the system.

[0009] In the prior art, microstrip antennas usually use a single-layer patch direct excitation method. This method is simple to design and process, but the working bandwidth is narrow, usually less than 5%. In addition, due to the narrow bandwidth, the robustness is not high and it is easily restricted by the processing accuracy, and broadband design cannot be achieved. Summary of the invention

[0010] Based on this, in order to solve the technical problems in the prior art, an antenna system is proposed.

[0011] The antenna system includes an electric bridge, an upper metal ground, an upper substrate, a lower substrate, a lower metal ground, a radiation patch, a mode converter, and a circular waveguide; the antenna system has a multi-layer board structure, which includes, from top to bottom, an upper metal ground, an upper substrate, a lower substrate, and a lower metal ground; the radiation patch is located on the upper side of the upper substrate, the mode converter is placed above the radiation patch and is connected to the circular waveguide above it; the two ports of the electric bridge are located between the upper substrate and the lower substrate.

[0012] In one embodiment, the mode converter is a truncated cone waveguide, which completes the mode transition from the microstrip line to the truncated cone waveguide and finally to the circular waveguide, and realizes the gradual transition from the TM01 mode to the TE11 mode under the excitation of the radiation patch.

[0013] In one embodiment, the upper metal ground is annular and located at the inner diameter edge of the mode converter; the antenna system has a plurality of metal vias, and the metal vias are arranged in a ring shape, surrounding the outer edge of the upper metal ground, and the metal vias pass through the upper substrate and the lower substrate from top to bottom.

[0014] In one embodiment, the bridge constitutes a feeding network, and the bridge has a first port, a second port, a third port, and a fourth port; the first port and the second port are receiving ports or transmitting ports, respectively; the third port and the fourth port are located between the upper substrate and the lower substrate, below the radiation patch and separated from the radiation patch by the upper substrate.

[0015] In one embodiment, the bridge is a 3dB bridge; a signal is input from the first port or the second port, and a two-ended excitation signal with equal amplitude and a phase difference of 90 degrees is generated at the third port and the fourth port through the 3dB bridge, thereby generating a circularly polarized wave; the third port and the fourth port feed the radiation patch through a coupled feeding method.

[0016] In one embodiment, the antenna system is applied to a frequency modulated continuous wave radar;

[0017] In one embodiment, the operating frequency of the antenna system is 77 GHz;

[0018] In one embodiment, the antenna system may be used as a feed source for a lens antenna or a horn antenna.

[0019] Implementing the embodiments of the present invention will have the following beneficial effects:

[0020] The present invention adopts a coupled feeding method, and a bridge feeding network generates dual-port signals with equal amplitude and 90 degrees phase difference to simultaneously excite the radiation patch to generate a circularly polarized wave, and utilizes the polarization reversal characteristics of the circularly polarized wave reflection echo to achieve polarization isolation of the transceiver end, thereby ensuring the isolation of the transceiver port. The antenna system of the present invention also includes a truncated cone mode converter with simple structure, good performance and high conversion efficiency, which realizes the mode transition from the microstrip line to the truncated cone waveguide and finally to the standard circular waveguide. Under the excitation of the broadband microstrip antenna, the microstrip antenna is gradually changed from the TM01 mode to the TE11 mode by adding a mode converter, thereby reducing the coupling effect of the waveguide on the microstrip antenna and reducing the generation of high-order modes. Therefore, the bandwidth of the antenna system is directly determined by the excitation of the dual circularly polarized microstrip antenna, thereby reducing the coupling interference of the traditional circular waveguide.

[0021] The wideband, dual circularly polarized, microstrip-to-circular-waveguide feed antenna system proposed in the present invention has a dual rotation direction of the transmitting and receiving end signals, which can ensure that the transmitting and receiving ports of the antenna system maintain a high degree of isolation. At the same time, the antenna system utilizes a very simple microstrip-to-waveguide gradual transition conversion structure, which can be used as a feed source for a lens antenna or a horn antenna to improve the gain of the antenna and the sensitivity of the receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] in:

[0024] Figure 1A It is a schematic diagram of an antenna feeding network system implemented by using a 3dB bridge in the prior art.

[0025] Figure 1B The figure is a schematic diagram of an antenna feeding network system realized by using a circulator in the prior art.

[0026] Figure 1C The figure is a schematic diagram of realizing an antenna feeding network system by using a coupler in the prior art.

[0027] Figure 1D The figure is a schematic diagram of an antenna feeding network system implemented by using dual antennas in the prior art.

[0028] Figure 2 It is a schematic diagram of a rectangular-circular conversion structure in the prior art;

[0029] Figure 3A It is a front view of a microstrip-to-waveguide structure excited by a microstrip probe in the prior art;

[0030] Figure 3B It is a left view of a microstrip-to-waveguide structure excited by a microstrip probe in the prior art;

[0031] Figure 4 is a three-dimensional view of the antenna system of the present invention;

[0032] Figure 5 is a side view of the antenna system of the present invention;

[0033] Figure 6 is a top view of the antenna system of the present invention;

[0034] The components include an antenna system 1, a bridge 2, an upper metal ground 3, an upper substrate 4, a lower substrate 5, a lower metal ground 6, a radiation patch 7, a mode converter 8, a circular waveguide 9, a metal via 10, a first port 21, a second port 22, a third port 23, and a fourth port 24. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The invention discloses a feed antenna system with high isolation, wide frequency band and microstrip-to-waveguide working in the 77 GHz frequency band.

[0037] See also Figure 4 , 5 As shown, the antenna system 1 includes a bridge 2, an upper metal ground 3, an upper substrate 4, a lower substrate 5, a lower metal ground 6, a radiation patch 7, a mode converter 8, a circular waveguide 9, and a metal via 10;

[0038] See also Figure 5 The side view of the antenna system 1 shown in the figure, the antenna system 1 is a multi-layer board structure, which is composed of an upper metal ground 3, an upper substrate 4, a lower substrate 5, and a lower metal ground 6 from top to bottom; the radiation patch 7 is located on the upper side of the upper substrate 4, and the mode converter 8 is placed above the radiation patch 7 and connected to the circular waveguide 9 above it; wherein the mode converter 8 is a truncated cone-shaped waveguide, which is used to realize a gradual conversion from the TM01 mode to the TE11 mode;

[0039] The upper metal ground 3 is annular and located at the inner diameter edge of the mode converter 8; the antenna system 1 has a plurality of metal vias 10, which are arranged in an annular shape and surround the outer edge of the upper metal ground 3. The metal vias 10 penetrate the upper substrate 4 and the lower substrate 5 from top to bottom. The metal vias 10 are used to reduce the generation of surface waves, and there are no metal vias 10 at the feeding microstrip line of the feeding network of the bridge 2 to ensure that no interference is generated.

[0040] See also Figure 4-6 As shown, the bridge 2 constitutes a feeding network, and the bridge 2 has a first port 21, a second port 22, a third port 23, and a fourth port 24; wherein the first port 21 and the second port 22 are respectively a receiving port or a transmitting port, that is, when the first port 21 is a receiving port, the second port 22 is a transmitting port, or when the second port 22 is a receiving port, the first port 21 is a transmitting port; the third port 23 and the fourth port 24 are located between the upper substrate 4 and the lower substrate 5, below the radiation patch 7 and separated from the radiation patch 7 by the upper substrate 4;

[0041] The bridge 2 is a 3dB bridge; a signal is input from the first port 21 or the second port 22, and a double-ended excitation signal with equal amplitude and a phase difference of 90 degrees is generated at the third port 23 and the fourth port 24 through the 3dB bridge, thereby generating a circularly polarized wave; the third port 23 and the fourth port 24 are separated from the radiation patch 7 by the upper substrate 4, and the radiation patch 7 is fed by a coupled feeding method;

[0042] The 3dB bridge is also called a frequency combiner. It can continuously sample the transmission power along a certain direction of the transmission line, split the input signal of the bridge input port into two signals of equal amplitude and 90 degrees phase difference and output them. The 3dB bridge can be used for multi-signal combination to improve the utilization rate of the output signal.

[0043] The antenna system 1 in the present invention adopts a multi-layer board design, and feeds the radiation patch 7 through a feeding network composed of a bridge 2 by a coupled feeding method, and realizes impedance matching by using appropriate impedance matching technology. The working bandwidth of the antenna system 1 can be increased by 50%-70% compared with the single-layer feeding method, which not only improves the system working bandwidth, but also improves the robustness of the system.

[0044] The antenna system 1 is applied to a frequency modulated continuous wave radar. The antenna system 1 is a dual circularly polarized antenna. The circularly polarized wave emitted by the radar changes its rotation direction when reflected back. The polarization isolation of the left and right rotation of the circularly polarized antenna is used to ensure the isolation of the transceiver port. The generation of surface waves is reduced by adding metal vias 10. Through simulation, it can be seen that this structure improves the antenna bandwidth, so that the antenna bandwidth reaches 16%.

[0045] The mode converter 8 in the present invention is a transition structure of microstrip to waveguide with simple structure and high conversion efficiency, which realizes the conversion of microstrip line to circular waveguide 9. Due to the limitation of working frequency, many conversion methods in the prior art cannot be used in the 77GHz frequency band, such as the rectangular-circular transition method adopted by the commonly used microstrip to waveguide, because the rectangular waveguide TE10 mode is very close to the circular waveguide TE11 mode, and the rectangular waveguide structure has sufficient bandwidth, which can avoid the generation of high-order modes. However, in the technical solution of the present invention, the rectangular waveguide structure cannot be used due to the need for circular polarization transmission. The direct transition using the circular waveguide will excite the high-order mode, and the strong coupling effect of the circular waveguide will affect the performance parameters of the radiation patch and reduce the working bandwidth. Therefore, an efficient and simple mode converter is very important. The technical solution of the present invention realizes the gradual conversion of the microstrip from the TM01 mode to the TE11 mode by adding the mode converter 8. Compared with the direct conversion of the ordinary circular waveguide, its bandwidth is significantly improved, which can minimize the interference to the radiation patch 7.

[0046] The directivity pattern of the microstrip radiated from the circular waveguide will be slightly deteriorated. On the one hand, it is caused by the poor return loss of the antenna port. On the other hand, there will still be certain high-order modes generated in the transition section, which will have an adverse effect on the directivity pattern. By increasing the height of the mode converter (frustum waveguide) or lengthening the circular waveguide to attenuate the high-order mode during transmission or adding a corrugated structure to the mode converter (frustum waveguide), the influence of the high-order mode on the directivity pattern can be effectively reduced.

[0047] Taking processing factors into consideration, the technical solution of the present invention adopts an extended circular waveguide 9 and a mode converter 8 to accelerate the attenuation of high-order modes. From the comparison results of the directional patterns before and after the waveguide extension, it can be seen that the symmetry and equalization of the directional patterns are improved after the extension, which indirectly reflects that the axial ratio performance is also improved. From the overall axial ratio simulation results of the antenna system 1, it can be seen that the 3dB axial ratio bandwidth reaches 10%, and the performance is good.

[0048] Implementing the embodiments of the present invention will have the following beneficial effects:

[0049] The present invention discloses a 77GHz dual circularly polarized microstrip to circular waveguide feed antenna system, the simulated axial ratio 3dB bandwidth of which is 10%, meeting the broadband circular polarization requirement, having better robustness, and having better anti-interference capability than linear polarization antennas. The characteristic of circularly polarized echo changing the rotation direction is utilized, and the system has an inherent polarization isolation advantage, thereby ensuring the isolation of the transceiver port. At the same time, the antenna system has a mode converter with a simple structure and high conversion efficiency, which can realize the conversion from microstrip to waveguide, reduce the interference of high-order modes, and ensure the broadband requirement of the antenna system. The antenna system as a whole has good radiation performance and is widely used. It can be used as a feed source for various antennas such as lens antennas and horn antennas, effectively improving the gain of the antenna and the sensitivity of the receiver.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An antenna system, characterized in that: The antenna system comprises an electric bridge, an upper metal ground, an upper substrate, a lower substrate, a lower metal ground, a radiation patch, a mode converter, and a circular waveguide; the antenna system has a multi-layer board structure, which comprises an upper metal ground, an upper substrate, a lower substrate, and a lower metal ground from top to bottom; the radiation patch is located on the upper side of the upper substrate, the mode converter is placed above the radiation patch and connected to the circular waveguide above it; the two ports of the electric bridge are located between the upper substrate and the lower substrate; The mode converter is a truncated cone waveguide, which completes the mode transition from the microstrip line to the truncated cone waveguide and finally to the circular waveguide, and realizes the gradual change from the TM01 mode to the TE11 mode under the excitation of the radiation patch.

2. The antenna system according to claim 1, characterized in that in, The upper metal ground is annular and located at the inner diameter edge of the mode converter; the antenna system has a plurality of metal vias, which are arranged in a ring shape and surround the outer edge of the upper metal ground. The metal vias pass through the upper substrate and the lower substrate from top to bottom.

3. The antenna system according to claim 1, characterized in that in, The bridge constitutes a feeding network, and has a first port, a second port, a third port, and a fourth port; the first port and the second port are receiving ports or transmitting ports respectively; the third port and the fourth port are located between the upper substrate and the lower substrate, below the radiation patch and separated from the radiation patch by the upper substrate.

4. The antenna system according to claim 3, characterized in that in, The bridge is a 3dB bridge; a signal is input from the first port or the second port, and a double-ended excitation signal with equal amplitude and a phase difference of 90 degrees is generated at the third port and the fourth port through the 3dB bridge, thereby generating a circularly polarized wave; the third port and the fourth port feed the radiation patch through a coupled feeding method.

5. The antenna system according to any one of claims 1 to 4, characterized in that: The antenna system is applied to a frequency modulated continuous wave radar.

6. The antenna system according to any one of claims 1 to 5, characterized in that The operating frequency of the antenna system is 77 GHz.

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