706 BELL SYSTEM TECHNICAL JOURNAL 



and the close association of the receiver and the transmitter in the radar 

 system introduces some additional new considerations. 



The power supply components are shown divided into two types "low 

 voltage" and "high voltage." This is a convenience which is desirable 

 because of the different design problems encountered and the quite different 

 equipment and circuits employed. The low d-c voltages required for the 

 operation of the electronic components of a radar system vary from 100 

 volts to 500 volts with both polarities with respect to ground often required. 

 The cathode- ray tube and "keep alive" circuits of the TR tube require 

 voltages from 1000 to 7000 volts usually at low current. The voltage 

 regulation of these power supply components to permit stable radar system 

 operation under the extreme and variable military operating conditions en- 

 countered presents a problem of considerable magnitude to the radar re- 

 ceiver designer. 



2. Radar Receiver Component Design 

 2.1 The Radar Receiver Input Circuit 



The conversion of the received microwave radar signal to a lower fre- 

 quency region where more efficient amplification is possible represents an 

 extremely important function of the radar receiver. The basic military 

 requirement of radar, that of providing the greatest possible useful sensi- 

 tivity, depends fundamentally on the efficient handling of the low-energy 

 microwave received signal in the input of the radar receiver. The micro- 

 wave character of the received signal and the extremely low amplitudes en- 

 countered contribute to the difficulties of radar input circuit design. 



The techniques of microwave transmission available to the communica- 

 tions engineer have but recently been developed and are at this time still 

 extremely limited in comparison to those methods commonly employed at 

 the normal radio frequencies. Even short physical connections required 

 between elements in the microwave region become "electrically long," a 

 matter of several wavelengths in the usual case, and here the design prob- 

 lem becomes acute. Network element of inductance, capcitance, and re- 

 sistance are not available in the form so efficiently employed at the lower 

 frequencies. Waveguides and cavities at radar frequencies replace them, 

 and the design of selective frequency networks in the microwave region 

 becomes a matter of precise arrangement and control of complex mechanical 

 forms. 



Suitable means for vacuum tube ami)lilication at frequencies above 1000 

 mc have not been available to date; this represents another extremely re- 

 stricting situation for the radar receiver designer. 



