Design Of L Band Radar Receiver With Large Dynamic Range

Receiver is the an important part of radar system,it's main function is the frequency selection,power amplification,frequency conversion,demodulation and so on.With the development of radar technology,modern radar system generally requires the receiver has the characteristics of low noise,high dynamic,high stability and strong anti-interference ability.The study of the radar receiver with large dynamic range has been an important work,because the signal power into the radar receiver often changes in a wide range,in order to make the radar receiver can handle a variety of power of echo signal Simultaneously,which requires the radar receiver must have a large dynamic range.The dynamic range of the general radar receiver is about 60 dB,however,the modern radar requires more than 100 dB.The key to realize the large dynamic range of the radar receiver is to design the RF front-end of the receiver reasonably,so this paper mainly studies the receiver RF front-end.The main work includes the design of the scheme,the selection of the device,the design of the cavity filter,automatic gain control circuit and PLL frequency synthesizer and so on.The main difficulty of the design is to realize 110 dB input dynamic range,a common method is the multi-stage automatic gain control(AGC)circuit cascade,which compresses the large dynamic range of the input signal into a small dynamic range of the output signal.However,on the one hand the circuit becomes complicated,increasing the difficulty of debugging,and multi-stage AGC circuit will greatly reduce the receiver's response speed,on the other hand increased the size of the receiver,which is contrary to the trend of miniaturization.The receiver designed in this subject is based on the superheterodyne secondary frequency conversion structure,and it realize the large dynamic range of the receiver by combining the cavity filter design and the automatic gain control circuit design.The lower limit of the dynamic range of the receiver is determined by the sensitivity,and the sensitivity is related to the noise figure of the receiver.Using the cavity filter which insertion loss is very small as the RF preselection filter,can significantly reduce the receiver noise figure,thereby improving the receiver sensitivity,so that the receiver's dynamic range will have a lower lower limit.However,the cavity filter has a significant drawback is the larger size,which will increase the size of the receiver,so this paperpresents a method of miniaturized cavity filter,which can keep the volume of the receiver within the acceptable range.And the upper limit of the dynamic range of the receiver is determined by the 1dB compression point of the receiver,in order to improve the upper limit of the dynamic range of the receiver,it is necessary to obtain a reasonable gain distribution,and then an automatic gain control circuit can be used.This article only uses a first-order automatic gain control circuit,which achieves a 96 dB gain control range.Thus,the input dynamic range of the receiver is realized by the combination of the cavity filter and the automatic gain control circuit,which simplifies the structure of the large dynamic range receiver and reduces the volume.The final test results show that the dynamic range of the receiver RF front-end system up to 110 dB,the sensitivity reached-120 dBm,the noise figure is 4.2dB,all the indicators meet the design requirements,the receiver RF front-end system meets the most requirements of dynamic range in the radar system.