A COUPLED RESONATOR REFLEX KLYSTRON 729 



across the interaction gap as, 



Y = Gr{f) + jBr(f), 



where Grif) and Brif) denote the total conductance and total suscep- 

 tance both of which are functions of frequency. Over the region of 

 constant RF gap voltage we require | F | or 



VGlif) + BUf) 



to be constant. This, however, means that the power generated (as 

 distinct from the power deUvered to the load) is not constant since it 

 is given by. 



Generated Power = J^(RF gap voltage)^ (Total Conductance) 



= y2v'GT{i) 



and Gt varies with frequency. Now, the term Gt(J) is the sum of a 

 number of conductances, all but one of which do not change with fre- 

 quency. The frequency-invariant conductances represent the different 

 power losses in the primary resonator plus the external load referred to 

 the gap while the remaining frequency-sensitive conductance is due to 

 the coupled circuit used in shaping the admittance locus. Hence the 

 useful power output is proportional to V^ and therefore constant if V^ 

 is constant, whereas the variation with frequency of the total conduct- 

 ance must be taken into account in evaluating generated power. 



The foregoing discussion together with the illustrations of Fig. 5 

 should make it clear that in order to maintain a constant RF power 

 output level, over a specified frequency range, we must have the elec- 

 tronic admittance interact with a circuit the input impedance of which, 

 when referred to the gap, is also constant over the same frequency range. 

 A circuit having such characteristics can be obtained by the use of 

 coupled resonators as will be shown later. 



Suppose the emphasis is on modulation hnearity rather than flatness 

 of power output. Attention, then, must be focused on the relation be- 

 tween input phase angle and frequency of the passive circuit. Here, 

 again, we shall see that the application of coupled resonators offers 

 advantages beyond what is possible with a single cavity. 



3.1 Driving Point Properties of Two Coupled Resonators Having Equal 

 Q's 



Using the equivalent shunt representation as shown in Fig. 6, the 

 exact expression for the input admittance, F, of two coupled resonators 



