D. J. H E A L E Y III 



CHAPTER 7 



THE RADAR RECEIVER 



7-1 GENERAL DESIGN PRINCIPLES 



The airborne radar receiver amplifies and filters the signals received by 

 the radar antenna for the purpose of providing useful signals to display and 

 automatic tracking devices. The receiver accepts all of the signals appear- 

 ing at the antenna terminals and must filter them so as to provide maximum 

 discrimination against signals which do not originate by surface reflection 

 of the transmitted radar signal from certain desired targets. 



Modulation characteristics of the desired signals must be preserved in 

 the filtering process. The modulation characteristics provide information 

 on the number of targets, their angular position with respect to a given 

 frame of reference, the distance between the radar set and the targets, 

 and the velocity of the targets. 



The majority of airborne radar receivers are of the superheterodyne 

 type. Ordinary pulse radar sets are usually of the single frequency con- 

 version type. Doppler radar sets employ single sideband reception. The 

 receivers are more complicated than in the ordinary pulse radar set and 

 generally employ multiple frequency conversion in order to realize the 

 required frequency selectivity. Fig. 7-1 shows a functional block diagram 

 of an elementary receiver of each type. 



Performance of a radar receiver is described by the following character- 

 istics: 



1. Noise figure 5. Dynamic range 



2. Sensitivity 6. Cross-modulation characteristics 



3. Selectivity characteristics 7. Tuning characteristics 



4. Gain control characteristics 8. Spurious response 



Specification of each of these characteristics depends upon the particular 

 radar application. Analysis of the radar system defines the input signal 

 environment, the required output signal-to-noise ratio, and required 

 fidelity of modulation. Such requirements are then interpreted in terms 

 of the above characteristics. Each of these characteristics is discussed 

 later in this chapter and in Chapter 8. 



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