THE RADAR RECEIVER

   THE  RADAR  RECEIVER        

        The function of the radar receiver is to detect desired echo signals in the presence of noise, interference,or clutter.It must separate wanted from unwanted signals, and amplify the wanted signals to a level where target information can be displayed to an operator or used in an automatic data processor. The design of the radar receiver will depend not only on the type of waveform to be detected,but on the nature of the noise, interference,and clutter echoes with which the desired echo signals must compete.In this chapter,the receiver design is considered mainly as a problem of extracting desired signals from noise.Noise can enter the receiver via the antenna terminals along with the desired signals, or it might be generated within the receiver it self.At the microwave frequencies usually used for radar, the external noise which enters via the antenna is generally quite low so that the receiver sensitivity is usually set by the internal noise generated within the receiver.Good receiver design is based on maximizing the output signal-to-noise  ratio.As described in Sec.10.2,to maximize the output signal-to-noise ratio, the  receiver must be designed as a matched filter, or its equivalent.The matched filter specifies the frequency response function of the I F part of the radar receiver. Obviously, the receiver should be designed to generate as little internal noise as possible, especially in the input stages where the desired signals are weakest.Although special attention must be paid to minimize the noise of the input stages,the lowest noise receivers are not always desired in many radar applications if other important receiver properties must be sacrificed.