| With the development of target detection,people are no longer satisfied with the detection of barrier-free objects.Wall-penetrating radar is also developed to detect life behind various complex shielding objects,providing technical support for urban antiterrorism and emergency rescue activities.Antenna,as an indispensable part of radar,is a hot research topic in recent years.Through-wall radar antenna needs to satisfy the high gain,wide bandwidth,beam,miniaturization,etc.,at the same time,in order to obtain higher detection resolution,need to increase the aperture antenna,usually adopt multiple input multiple output(MIMO)antenna array form virtual aperture,so as to realize the antenna in small size for higher resolution performance.The coupling between antenna elements in miniaturized ultra-wideband antenna array inevitably affects the signal quality and the noise of antenna circuit board.In order to realize the antenna circuit board that can be applied to the wallpenetrating radar,the ultra-wideband,miniaturized and high isolation MIMO antenna array is studied in depth.A 2-transmitter and 8-receiver antenna array is designed.After each receiving antenna,two LNA stages are added,and then SP8T RF electronic switch is connected.Realize the virtual 1 send 16 receive antenna array.Specific work contents include:(1)An ultra-wideband microstrip antenna array element is designed by combining the printed antenna and DGS structure.The reflection coefficient of the antenna port is less than-10dB in the 2.1-3.7GHz band,the maximum radiation direction gain is 9dB,the direction diagram of each frequency point is uniform,and the beam Angle at plane H is-60°～60° at 6dB.The antenna array element size is 43.6mm×40.4mm.(2)Combining the theory of virtual antenna array and MIMO theory,which has been developed rapidly in recent years,a MIMO antenna array consisting of SP8T electronic switches with sparse transmitting and compact receiving is proposed.By switching the electronic switch,the virtual antenna array of 1 transmitting and 16 receiving is realized,and the range resolution and Angle resolution of measurement are improved.When receiving a single excitation,the maximum gain of antenna array element is 8.9dB,the beam Angle of 3dB on plane E is 58°,and the beam Angle of 5dB on plane H is 100°.The beam scanning of-57°～57° can be achieved by changing the phase difference of each antenna array element and simulating the switch of electronic switch.The size of MIMO antenna array is 435.3mm×410.3mm.(3)Based on Klopfenstein gradient line theory,the impedance matching circuit between antenna,low noise amplifier and electronic switch is designed to reduce the reflection between each part and improve the receiving sensitivity of antenna.The real impedance of the receiving port ranges from 42.2 ohms to 55 ohms,and the virtual impedance ranges from-7.2 ohms to 9.0 OHms.S11 is smaller than-20dB.The reflection coefficient of the transmitting port S11 is less than-17dB,and the standing wave ratio is less than 1.4,which meets the engineering needs.(4)Finally,the actual antenna circuit board is made.The gain of the two-stage low noise amplifier circuit is about 34.5dB,and the gain flatness is less than 3dB.The antenna board works in the range of 2.1-3.7GHz,the echo loss of the transceiver port of the antenna board circuit is less than-10dB,and the maximum radiation direction gain of the transmitting antenna is more than 5dB.H plane 5dB beam width is about 100°.The existing signal source in the laboratory transmits frequency modulated continuous wave signals,transmits signals through the transmitting antenna array on the antenna board,receives signals through the receiving antenna array,and connects to the existing RF front-end processing board in the laboratory.Finally,when the SNR is greater than 5dB,the human body targets at 0.6～34.8m can be tested.The experimental results show that the test results are basically consistent with the simulation results,which verifies the correctness and practicability of the designed UWB MIMO antenna array. |
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