THE RADAR RECEIVER 703 



The cathode-ray tube has been most universally employed as the display 

 device in the modern radar system. The incoming electrical information 

 from the various receiver inputs is here electronically converted into a 

 visual form capable of being modified over small intervals of time as the 

 change in the radar scene occurs. Multiple presentations having various 

 map-scale factors are found in many modern radar systems to enable de- 

 tailed examination of a small magnified target area, while retaining the 

 ability to observe the broad area features at will. 



The use of radar for the purpose of control of gunfire, release of bombs, or 

 steering of a vessel or aircraft requires that essentially continuous coordinate 

 information be transmitted from the radar observer to the device under his 

 control. This is usually accomplished through the registration of mechan- 

 ical or projected electronic markers upon the visual radar display, this 

 process of successive alignment furnishing the required information to the 

 controlled device. In the case where automatic means of maintaining 

 coincidence between marker and target are employed it should be observed 

 that the original selection of the target and the initial coincidence adjust- 

 ment still remains a matter for interpretation on the part of the human oper- 

 ator, and here again the visual radar display form is desirable. 



The presentation means of a radar receiver has, therefore, been chosen 

 to allow complete display of the data as quickly as it is received and in a 

 form most convenient to the understanding of the human operator. In 

 a broad sense, the radar system output terminal conditions and require- 

 ments are similar to those encountered for any communication system 

 i.e. to supply the human observer with all the information available to the 

 system in a form which will permit maximum usefulness with a minimum of 

 delay. 



1.3 Composition of the Radar Receiver 



For convenience in the discussion to follow, the generalized radar receiver 

 will be partitioned as shown in Figure 4. This particular choice of com- 

 ponent division is somewhat arbitrary, but is chosen because of its func- 

 tional simplicity. Mechanical, and in some cases electrical, conditions 

 encountered in any particular radar system design often indicate physical 

 arrangements which will dififer considerably from the arrangement illus- 

 trated. 



The converter component of the radar receiver has, as its primary func- 

 tion, the conversion of the received microwave signal to an intermediate 

 frequency region where further amplification and discrimination is possible. 

 The converter consists of a beating oscillator operating in the microwave 

 frequency region and a nonlinear element, which at the higher radar fre- 

 quencies consists of a point-contact crystal element. At the lower radar 



