A COUPLED RESONATOR REFLEX KLYSTRON 739 



of Fig. 6(c) except that the ordinate now represents the instantaneous 

 slope normaUzed with respect to its midmode value. The curves shown 

 are for values of (Qkf ranging from zero to (Qkf = 0.18. Let us, for 

 example, examine the curve corresponding to (Qkf = 0.12; the slope 

 is seen to stay absolutely constant up to a frequency deviation of 2Q8 = 

 dbO.3, while the plot for the single resonator, i.e., (Qkf = 0, included in 

 this figure for comparison, changes by 8.4 per cent over the same fre- 

 quency range. 



Putting this in another way, suppose the maximum allowable devia- 

 tion in slope from its mid-band value is one per cent. Fig. 8 then in- 

 dicates that the permissible frequency deviation for coupled resonators 

 having a value of {Qkf = 0.135 is given by 2Q8 = ±0.5, whereas it 

 must be restricted to one-fifth this value, i.e., 2Q8 = dzO.l, for the 

 single resonator case. In terms of a midband frequency of 4000 mc and 

 Q = 100, the permissible frequency excursions would be ±10 mc and 

 ±2mc, respectively. 



It is to be noted that the value of coupling coefficient resulting in 

 greatest modulation linearity is considerably smaller than the value of 

 coupling coefficient found to yield a constant impedance level. 



3.2 Mode Shapes Resulting from the Interaction Between Electronic 

 I Admittance and Input Admittance of Two Coupled Resonators of EqvM 

 Q's 



Having determined all relevant properties of the passive circuit as 

 they appear across the grids of the bunching gap, we may now proceed 

 to investigate the results arising from their interaction with the electronic 

 admittance. The approach to be adopted is essentially the same as the 

 one outlined earlier for the case of the conventional single-cavity reflex 

 klystron. It involves a graphical superposition of the negative of the 

 passive circuit admittance upon the small-signal-electronic-admittance 

 spiral in the g-h plane, such as shown in Fig. 9(a). The location of the 

 load lines with respect to the spiral has been chosen, somewhat arbi- 

 trarily, such that the ratio between the length of the Fes-vector cor- 

 responding to ^ = (2 + %) cycles and that of the input admittance 

 vector for {Qk^ = and 5 = equals two. Load lines have been drawn 

 for five values of (Qk)^ ranging from zero to unity. 



The determination of mode shapes from Fig. 9(a) proceeds as illus- 

 trated in Table I. Taking the repeller drift angle as the independent 

 variable we can obtain corresponding values of generated power (in 

 arbitrary units) and frequency (in terms of Q8) by going through the 

 steps indicated. 



