714 



BELL SYSTEM TECHNICAL JOURNAL 



techniques and the difficulty in maintaining precise control of each element 

 over the required band of frequencies are the fundamental problems of the 

 radar converter designer. The network problem here is concerned with 

 realizing the desired frequency conversion with a minimum of dissipation of 

 the useful signal. This implies that coupling of the nonlinear element to 

 the input and output terminals must be achieved in such a fashion that 

 matched impedance conditions result for the signals in their respective fre- 

 quency regions. Since the output signal has been shown to appear as a 



0.1 0.2 0.3 



POTENTIAL l^ 



0.4 0.5 

 VOLTS 



Fig. 9. — Typical voltage-current characteristic of a point-contact silicon crystal 

 rectifier. 



number of energy concentrations extending over a wide frequency range, it 

 would appear that an efficient design of output coupling network, would 

 involve optimizing the impedance relationshi})S over this wide-frequency 

 band. Several factors tend to simplify this problem by restricting the out- 

 put frequency band which must be considered in a practical radar converter 

 design. First, the greatest amount of energy is found to be present in the 

 lower order modulation products because of the rapid reduction in amj)litu(le 

 of the higher order terms in the equivalent expression for the nonlinear 

 element. This results in a concentration of energy at the input, output, 

 and beat oscillator frequencies and their respective second harmonic regions. 

 Second, the ratio of /i to /a in a microwave radar converter is of necessity 



