CN111707991A - Front-end structure of unmanned aerial vehicle-borne FM continuous wave radar - Google Patents

Abstract

The invention discloses an unmanned aerial vehicle-mounted frequency modulation continuous wave radar front end structure, which comprises a radar front end antenna structure, a radar front end transmitting circuit structure and a radar front end receiving circuit structure, wherein the radar front end antenna structure is connected with the radar front end receiving circuit structure; the radar front-end antenna structure is arranged on the top layer of the multilayer dielectric plate and also comprises a microstrip line, a microstrip line power dividing network and a microstrip patch array structure; the radar front-end transmitting circuit structure is composed of a multi-layer dielectric plate structure, an integrated chip and a metal piece structure. The radar front end receiving circuit consists of a multilayer dielectric plate structure and an integrated chip. The invention has compact structure, adopts miniaturized design to meet the load requirement of the micro unmanned aerial vehicle, can meet the linearity of broadband sweep frequency signals, and has remarkable high-resolution imaging capability.

Description

Front-end structure of unmanned aerial vehicle-borne FM continuous wave radar

technical field

The invention belongs to a microwave and millimeter-wave system circuit, and in particular relates to a front-end structure of an unmanned aerial vehicle-borne FM continuous wave radar for an unmanned aerial vehicle platform.

Background technique

Radar has a development history of more than 60 years and has been widely used in civil and military fields. Compared with sensors such as optics and lasers, radar has the advantages of all-weather, all-day and long-range action, and has a unique role in target detection.

Compared with the traditional pulsed synthetic aperture radar, the frequency-modulated continuous wave radar can realize a miniaturized and low-cost high-resolution imaging system. Therefore, the frequency-modulated continuous wave radar system plays an important role in airborne earth observation and regional imaging, and has become a commonly used working mode of radar, and its imaging technology is also an important development direction. At the same time, it is widely used in vehicle driving assistance systems and unmanned aerial vehicle imaging systems. In vehicle radar, 24GHz and 77GHz FM continuous wave radars have corresponding solutions. With the advantages of miniaturization and the rapid development of UAV technology, FM continuous wave radars are widely used in large and small UAVs. , FM continuous wave radar is also developing towards miniaturization and high resolution.

SUMMARY OF THE INVENTION

Purpose of the invention: The purpose of the present invention is to provide a front-end structure of an unmanned aerial vehicle-borne FM continuous wave radar, which adopts a miniaturized design to meet the load requirements of a miniature unmanned aerial vehicle. imaging capabilities.

Technical solution: a front-end structure of an unmanned aerial vehicle-borne FM continuous wave radar, including a radar front-end antenna structure, a radar front-end transmitting circuit structure and a radar front-end receiving circuit structure;

The radar front-end antenna structure is realized by the top layer of a multi-layer dielectric board; the radar front-end transmitting circuit structure is composed of a multi-layer dielectric board structure, a metal structure and a number of transmitting circuit devices; the radar front-end receiving circuit structure is composed of a multi-layer structure. It consists of a dielectric board structure and several receiving circuit devices.

Specifically, the transmitting circuit device includes a radio frequency integrated chip, a radio frequency power amplifier, an oven controlled crystal oscillator, a clock buffer, a direct digital frequency synthesizer, two low-pass filters, a clock signal power amplifier, and a phase-locked loop frequency synthesizer. , Micro Control Units and Power Devices. The receiving circuit device includes a clock divider by 4, a digital-to-analog signal converter, two differential low-pass anti-aliasing filters, two variable gain amplifiers, a micro control unit and a power supply device.

Further, the multi-layer dielectric board includes, from top to bottom, a top metal layer, a first dielectric core board layer, a second metal layer, a first dielectric adhesive layer, a third metal layer, a second dielectric core board layer, a third Four metal layers, the second dielectric adhesive layer, the fifth metal layer, the third dielectric core layer and the bottom metal layer; the top metal layer, the second metal layer, the third metal layer, the fourth metal layer, the fifth metal layer Both the metal layer and the underlying metal layer have etched circuit structures. Specifically, the top metal layer is etched with radio frequency circuit lines and radar front-end antenna structures, the second metal layer and the fifth metal layer are etched with radio frequency circuit grounds, and the third metal layer is etched with power supply related circuits The fourth metal layer is etched with control signal related circuit lines, and the bottom metal layer is etched with radio frequency circuit lines.

Further, the radar front-end antenna structure is composed of a top metal layer, a first dielectric core layer and a part of the second metal layer, and specifically includes a microstrip line, a microstrip line power division network and a microstrip patch array structure.

Further, the multilayer dielectric board structure further includes a plurality of first metallized vias connecting the top metal layer to the bottom metal layer and a plurality of second metallized vias connecting the third metal layer to the bottom metal layer;

The transmitting circuit device and the receiving circuit device are respectively fixed on the top metal layer and the bottom metal layer of the multilayer dielectric board structure by soldering, and pass through the top metal layer, the second metal layer, the third metal layer, the first metal layer, and the The four metal layers, the fifth metal layer, the bottom metal layer, the first metallized via hole and the second metallized via hole realize circuit connection.

Further, the structural size of the metal piece is 29-31mm wide, 33-37mm long and 7-9mm high.

More preferably, the metal structure is an aluminum metal structure processed by a CNC machine tool. The hollow grooves milled out of the metal part structure and the top metal layer of the multi-layer dielectric board structure form a shielding cavity, which shields and assists heat dissipation of some circuit devices; the depth of the hollow grooves milled out of the metal part structure is 4-6mm .

Beneficial result: the present invention provides a miniaturized UAV-borne 24GHz FM continuous wave radar radio frequency front-end structure, and its lightweight and miniaturized design makes the radar system easy to install on the UAV platform, and can meet the requirements of micro UAVs. The front-end includes one transmit channel and two receive channels, which can meet the linearity of the broadband swept signal and have remarkable high-resolution imaging capabilities.

Description of drawings

Figure 1 is a block diagram of the transmitter circuit and receiver circuit structure of the radar front-end system;

Figure 2 shows the structure of the radar front-end antenna, the isolation between S11 and the transceiver antenna;

3 is a structural diagram of the radar front-end according to the present invention;

Fig. 4 is the radar front-end test scenario of the present invention;

FIG. 5 is the result of testing and sorting out the frequency sweep characteristics of the radar front-end FM continuous wave signal according to the present invention;

Fig. 6 is a radar-to-target static test scene diagram equipped with the radar front-end of the present invention;

Fig. 7 is the received signal processing result of the corresponding scene of Fig. 6;

8 is a schematic diagram of a radar-to-target scanning test scenario equipped with the radar front-end of the present invention;

FIG. 9 is the received signal processing result of the scene corresponding to FIG. 8 .

Detailed ways

A miniaturized unmanned aerial vehicle carrier FM continuous wave radar front-end structure comprises a radar front-end antenna structure 1 , a radar front-end transmitting circuit structure 2 and a radar front-end receiving circuit structure 3 . The radar front-end antenna structure is realized by the top layer of the multi-layer dielectric board, and the front-end antenna structure also includes a microstrip line, a microstrip line power division network, and a microstrip patch array structure. The radar front-end transmitting circuit structure 2 is composed of a multi-layer dielectric board structure, a number of integrated chips and a metal structure. The radar front-end receiving circuit 3 is composed of a multi-layer dielectric board structure and several integrated chips.

Specifically, the multilayer dielectric board structure is closely arranged from top to bottom in the order of metals and dielectric materials, and from top to bottom are the top metal layer, the first dielectric core board layer, the second metal layer, the first A dielectric adhesive layer, a third metal layer, a second dielectric core layer, a fourth metal layer, a second dielectric adhesive layer, a fifth metal layer, a third dielectric core layer, and a bottom metal layer. The multilayer dielectric board structure includes a number of metallized vias connecting the top metal layer to the bottom metal layer and a number of metallized vias connecting the third metal layer to the bottom metal layer.

Among them, the top metal layer of the multilayer dielectric board structure, the first dielectric core board layer, and part of the second metal layer constitute the radar front-end antenna structure. The chip arrays are all provided by the top metal layer of the multilayer dielectric plate structure.

Preferably, the metal structure is an aluminum metal structure processed by CNC machine tools, and the hollow grooves milled in the metal structure and the top metal of the multi-layer dielectric plate structure form a shielding cavity to shield some integrated chips and assist heat dissipation. The size of the metal part structure is 29-31mm wide, 33-37mm long and 7-9mm high; the depth of the hollow groove milled out of the metal part structure is 4-6mm.

Further preferably, the integrated chip is fixed on the top metal layer and the bottom metal layer of the multilayer dielectric board structure by soldering. The six metal layers of the multilayer dielectric board have etched circuit structures, plus the above two metallized vias, combined with multiple integrated chips to form a radar front-end transmitting circuit structure and a radar front-end receiving circuit structure.

In order to describe the technical solutions disclosed in the present invention in detail, further description is given below in conjunction with the accompanying drawings and specific embodiments of the description.

As shown in Figure 1, the radar front-end transmitting circuit part, the radar's broadband fast frequency sweep signal is generated by the mixed frequency synthesis scheme of DDS+PLL as the frequency source. The signal provided by the oven controlled crystal oscillator is used as the reference signal of the direct digital frequency synthesizer through the buffer and high-speed logic level converter. , and then filtered as the reference signal of the phase-locked loop. Through the external phase-locked loop circuit VCO, the frequency sweep signal with a center frequency of 24.25GHz and a bandwidth of 700MHz can be output, and then amplified by an external power amplifier and finally radiated to the free space by the transmitting antenna.

The size of the radar front-end structure of this embodiment is 80 mm×160 mm, which meets the requirements of miniaturization and light weight of the micro-UAV. The radar front end is powered by 12V and 3.6V dual power supplies. The radar front-end has one transmit channel and two receive channels. In the receive chain, the receive signal is received by two receive antennas, and the low-noise amplification, down-conversion and frequency mixing are completed inside the RFIC. The variable gain intermediate frequency amplifier amplifies the differential signal, which is then filtered by a fifth-order differential elliptical low-pass filter composed of lumped elements (differential filter passband 3.5MHz, stopband attenuation 40dB@5MHz), and finally a dual-channel ADC with 25MHz The sampling rate of the ADC is sampled, and the sampling clock of the ADC is obtained by the output of the oven controlled crystal oscillator through the buffer, high-speed logic level converter, and finally divided by two D flip-flops.

The transmitting and receiving antennas of the radar front-end adopt the microstrip patch array with the same structure and feeding in series. The antenna of the microstrip structure is also easy to be directly integrated in the front-end card, and the number of each antenna array element is 2×6. The -10dB impedance bandwidth of the antenna is 1.4GHz, and the gain can reach 17dB. In order to ensure good isolation, the coupling between the designed transceiver antenna array can reach -55dB in the working frequency band, as shown in Figure 2, where S11 represents return loss, S21, S31 represents the isolation of the two receiving antennas relative to the transmitting antenna. See Table 1 for the half-power beamwidth of the antenna E-plane (azimuth plane) and H-plane (elevation plane). At the same time, RFIC, RF power amplifier, transceiver antenna are on the same side of the entire dielectric board, and other circuits are on the other side of the multilayer dielectric board to ensure that control signals and high-power low-frequency analog signals will not interfere with RF signals. The size of the entire RF front-end is 80mm×160mm. The small-sized front-end system brings convenience to the UAV. The structure of the radar front-end is shown in Figure 3. Figure 3(a) is the front structure of the radar front-end, and Figure 3(b) is the radar front-end. The back structure of the front end. In FIG. 3, the radar front-end antenna structure of the present invention is composed of a top metal layer, a first dielectric core layer and a partial area of the second metal layer, including one transmitting antenna and two receiving antennas, where the "partial area" refers to That is, the gray area corresponding to the three antennas in Figure 3.

E plane (azimuth plane) H plane (pitch plane) 24.05GHz 13.451° 38.601° 24.15GHz 13.499° 38.677° 24.25GHz 13.218° 38.676° 24.35GHz 12.785° 38.545° 24.45GHz 12.805° 38.584°

In order to ensure that the entire FM continuous wave radar radio frequency front end can work normally, the present invention uses the FSW spectrum signal analyzer of Rohde & Schwarz Company to perform transient analysis and test on the radar front end. The radar front-end generates FM continuous wave signal and radiates it to free space through the transmitting antenna on the front-end card. The receiving end uses the designed antenna with the same structure to receive and directly connect to the FSW spectrum signal analyzer through a short cable. Complete evaluation of the entire radar front-end transmit chain performance including antennas.

The carrier frequency of the swept-frequency signal actually generated by the radar front-end system is 24.25GHz, and the bandwidth is up to 700MHz. The frequency modulation signal mode is continuous frequency rise-fast fall-continuous rise. Due to the limited chirp bandwidth of the transient analysis mode supported by the actual frequency meter ( 500MHz), it is divided into two carrier frequencies of 24.1GHz and 24.4GHz for transient analysis during the test. When the carrier frequency is 24.1GHz, the sweep frequency characteristics and linearity of the lower frequency band (23.9GHz-24.3GHz) are tested. When the carrier frequency is 24.4GHz Test the frequency sweep characteristics and linearity of the higher frequency band (24.3GHz-24.6GHz), and the results show that the peak value of the frequency deviation is less than one thousandth of the frequency sweep bandwidth. Finally, the test data is sorted to obtain a complete frequency sweep in a single cycle. signal, as shown in Figure 5. The test results show that the sweep bandwidth can reach more than 700MHz, the sweep period is 600us, and the range with good linearity can cover more than 80% of the entire sweep rise time (400us). Sweep bandwidth and sweep linearity can meet the actual use requirements.

In order to verify the radar's ability to detect targets, the radar system equipped with the invented radar front-end structure was tested for static target detection in a microwave anechoic chamber and scanning tests on the azimuth and elevation planes in the anechoic chamber. The digital signal data of the radar receiving channel is generated by the front-end structure and processed by the PC. Triangular reflectors are used as detection targets during testing in the dark room.

The target static test experimental scene built in the environment of the microwave anechoic chamber is shown in Figure 6. The angle between the wedges on both sides of the radar is 38° larger than the beam width of the main lobe on the H-plane of the antenna to reduce environmental clutter interference in other directions. The target is placed on the side facing the antenna in the radar front-end structure, and is on the same horizontal plane, about 2m away from the radar front-end structure.

Figure 7 shows the result of the received IF digital signal processed by MATLAB. Figure 7(a) shows the echo signal in a single pulse, the horizontal axis is the number of sampling points, a total of 4096 data points; the vertical axis is the signal amplitude, which is the quantized digital output value of the ADC. It can be seen that the echo presents an obvious sinusoidal signal form, the received echo signal form is correct, and there is no obvious spurious and spike interference. Figure 7(b) is the stack of echoes of all pulses. The horizontal axis corresponds to the echoes of all 100 frequency sweep cycles. The vertical axis is the number of sampling points, up to the 4096th sampling point. The depth of the color block represents the signal amplitude. The results show that the echo signal amplitude in each frequency sweep period presents a regular periodic fluctuation, and the echo signal amplitude distribution in each frequency sweep period is basically the same. Figure 7(c) shows the frequency domain results after Fourier transform of all pulse period signals. The horizontal axis still corresponds to the number of frequency sweep cycles, and the vertical axis is the value of the horizontal axis after FFT transformation of each frequency sweep cycle. The maximum value is 4096, only the obvious and meaningful part of the data is displayed here, and the color depth represents the value of the vertical axis after FFT transformation of each frequency sweep period. The spectrum in the figure is concentrated at 27.5KHz, corresponding to the target distance of 2.3m. Figure 7(d) is the Doppler accumulation result of 100 pulses. It can be seen from the figure that the accumulation result is correct.

The schematic diagram of the target scanning test experimental scene built in the environment of the microwave anechoic chamber is shown in Figure 8. The radar is placed on a precision electromobile platform and aligned horizontally with the target. The electric mobile turntable can move accurately within the range of plus or minus 20 degrees in the azimuth plane and plus or minus 15 degrees in the elevation plane, so that the target can be scanned on the azimuth plane and the elevation plane respectively. The processing result of the echo signal is shown in Figure 9. Figure 9(a) is the spectral distribution of the echo signal of the azimuth plane. A total of 30,000 azimuth pulses were selected during data processing, and the time of each pulse was 600us. It can be seen from Figure 9(a) that the radar scans the target twice during the rotation process, and its cycle is about 17,000 azimuth pulses. The lighter part in Figure 9(a) corresponds to the main lobe of the radar and has about 5,500 pulses. This pulse is basically in line with the actual situation that the azimuth plane of the front end of the radar is 13°. Figure 9(b) shows the Doppler accumulation of the azimuthal plane scan. Figure 9(c) and Figure 9(d) are the echo spectrum distribution and Doppler accumulation of the elevation plane, respectively. The target can be detected when it is rotated within the range of plus or minus 15 degrees.

To sum up, the present invention designs and implements a 24GHz FMCW synthetic aperture radar front-end prototype carried by an unmanned aerial vehicle, including a radar front-end transmitting circuit, a radar front-end receiving circuit and a transceiver antenna structure. The size of 80mm×160mm meets the requirements of miniaturization and light weight of micro-unmanned aerial vehicles. The radar includes one transmitting channel and two receiving channels. The experimental test results show that the front-end FM continuous wave carrier frequency is 24.25GHz, the frequency sweep bandwidth is 700MHz, the frequency sweep period is 600us, and the peak value of the frequency deviation in the linear frequency sweep is less than one thousandth of the frequency sweep bandwidth.

Claims (10)

1. an unmanned aerial vehicle carrier frequency modulation continuous wave radar front-end structure is characterized in that: comprise radar front-end antenna structure (1), radar front-end transmitting circuit structure (2) and radar front-end receiving circuit structure (3); The radar front-end antenna structure (1) is realized by the top layer of a multi-layer dielectric board; the radar front-end transmitting circuit structure (2) is composed of a multi-layer dielectric board structure, a metal structure and a plurality of transmitting circuit devices; the radar front-end The receiving circuit structure (3) is composed of a multi-layer dielectric board structure and several receiving circuit devices. 2 . The front-end structure of the unmanned aerial vehicle FM continuous wave radar according to claim 1 , wherein the multilayer dielectric board comprises a top metal layer, a first dielectric core board layer, and a second metal layer from top to bottom. 3 . , the first dielectric adhesive layer, the third metal layer, the second dielectric core layer, the fourth metal layer, the second dielectric adhesive layer, the fifth metal layer, the third dielectric core layer and the bottom metal layer; the The top metal layer, the second metal layer, the third metal layer, the fourth metal layer, the fifth metal layer and the bottom metal layer all have etched circuit structures. 3. The unmanned aerial vehicle carrier FM continuous wave radar front-end structure according to claim 2, is characterized in that: the top metal layer is etched with radio frequency circuit lines and radar front-end antenna structure, the second metal layer and the fifth The metal layer is etched with radio frequency circuit grounds, the third metal layer is etched with power supply related circuit lines, the fourth metal layer is etched with control signal related circuit lines, and the bottom metal layer is etched with radio frequency circuit lines. 4. The front-end structure of the UAV carrier FM continuous wave radar according to claim 2 or 3, wherein the radar front-end antenna structure is composed of parts of a top metal layer, a first dielectric core layer and a second metal layer The area composition specifically includes the microstrip line, the microstrip line power division network and the microstrip patch array structure. 5. The front-end structure of the unmanned aerial vehicle carrier FM continuous wave radar according to claim 1, characterized in that: the transmitting circuit device comprises a radio frequency integrated chip, a radio frequency power amplifier, an oven controlled crystal oscillator, a clock buffer, a direct digital frequency Synthesizer, two low-pass filters, clock signal power amplifier, phase-locked loop frequency synthesizer, micro control unit and power supply devices. 6. The front-end structure of the unmanned aerial vehicle carrier FM continuous wave radar according to claim 1, wherein the receiving circuit device comprises a clock 4 frequency divider, a digital-to-analog signal converter, two differential low-pass anti-aliasing stack filter, two variable gain amplifiers, micro control unit and power supply components. 7. The front-end structure of the UAV carrier frequency modulation continuous wave radar according to claim 2, characterized in that: the multilayer dielectric plate structure further comprises a plurality of first metallized vias connecting the top metal layer to the bottom metal layer and a plurality of second metallized vias connecting the third metal layer to the bottom metal layer; The transmitting circuit device and the receiving circuit device are respectively fixed on the top metal layer and the bottom metal layer of the multilayer dielectric board structure by soldering, and pass through the top metal layer, the second metal layer, the third metal layer, the first metal layer, and the The four metal layers, the fifth metal layer, the bottom metal layer, the first metallized via hole and the second metallized via hole realize circuit connection. 8 . The front-end structure of the UAV carrier FM continuous wave radar according to claim 1 , wherein the size of the metal part is 29-31mm wide, 33-37mm long and 7-9mm high. 9 . 9 . The front-end structure of the unmanned aerial vehicle carrier FM continuous wave radar according to claim 1 or 8, characterized in that: the hollow grooves milled in the metal structure and the top metal layer of the multi-layer dielectric plate structure form a shielding cavity , shielding and assisting heat dissipation of some circuit devices; the depth of the hollow grooves milled out of the metal structure is 4-6mm. 10 . The front-end structure of the UAV carrier FM continuous wave radar according to claim 1 or 8 , wherein the metal structure is an aluminum metal structure processed by a numerically controlled machine tool. 11 .

Images