Research And Development Of The Ground Penetrating Radar Receiver Front-end

The carrier-free impulse ground penetrating radar is widely used in the commercial ground penetrating radar market due to the characteristics of simple pulse formation,low cost,high survey speed,and no side-lobe interference in the frequency domain.The ground penetrating radar is commonly used in water meteorology,resource exploration,road and bridge quality testing and many other aspects.Therefore,the exploration of ground penetrating radar has practical significance such as scientific research and commercial value.The development of a high reliability and low cost receiver is of great significance to the commercial application of ground penetrating radar.The main content and task of the paper is to research and develop a front-end circuit of the ground penetrating radar,including the limiter circuit,high-speed transceiver switch circuit,passive band-pass filter,variable gain amplifier circuit,sample-and-hold circuits,and sequential logic control circuits.The receiver front-end parts of the circuits through a large number of programs comparison,simulation optimization,processing and assembly,testing and debugging,and successfully completed the development work.The technical parameters of research and develop the receiver in this thesis are: the frequency range is 60 MHz to 180MHz;the receiver has no less than 10 points on the echoes with a pulse width of 5ns to 10ns;there are 0dB to 60 d B amplification in 10 dB steps and amplify functions;noise figure at maximum gain is no more than 4.0dB.The limiter circuit prevents the larger direct wave from damaging the post-amplifier.The high speed transceiver switch circuit disconnects the receiver circuitry during transmission to prevent saturation of the post-amplifier.The variable gain amplifier circuit adopts a cascade scheme of a radio frequency low noise amplifier and the digitally controlled attenuator.The control circuits adjust the gain through a three-wire SPI interface protocol.The total gain of the designed amplifier is greater than 60 dB,and each 6-bit digital attenuator can achieve 0dB~31.5d B attenuation.The radar echo signal is processed by the equivalent sampling method.The echo frequency is 100 kHz.Two-stage sampling circuits is used to achieve the equivalent sampling function of the signal.The previous stage uses bipolar pulse to trigger the four-tube balanced sampling gate circuit.At this time,the signal holding time is close to the microsecond level;the latter stage uses ultra-high speed sampling to maintain Chip AD783,higher than 250 ns sampling time.After actual testing,the performance of the circuit meets the design expectations.According to the actual test results,the measured data of the variable gain amplifier circuit,the system noise figure,and the passive band-pass filter circuit basically meet the design expectations.Through joint debugging,the front-end circuit of the receiver cooperates well with the control circuit and data acquisition circuit of the radar system,basically fulfilling the requirements of the system on the receiver.