DESIGN FACTORS OF THE 1553 TRIODE 



509 



for Mi. The spacing .vi is involved only in the second factor which again 



is a function only of 9i = 



We again have a strong first maximum at 



6 —> requiring Xi to be as small as possible (Fig. 7). Other maxima are 

 indicated at larger values of 6i (and larger values of Xi) again at points 

 where Gn -^ and the same remarks apply here as were made in the 

 previous section. For broad-band optima we are therefore interested in 

 minimum values of Xi. 



OUTPUT TRANSIT ANGLE, ©2 " ^2 



377 

 2 



6300 



777 277 



Fig. 8. — Gain-band product dependence on output spacing (X2). 

 VARI.A.TION WITH AnODE-GrID Sp.^CING, Xi 



The anode-grid spacing x-i is involved only in the third factor of either 

 formulation. This factor is a function of output transit angle Q-i and 

 exhibits a maximum for Q = 2.9 radians as shown in Fig. 8. This opti- 

 mum at a fairly large value of Qi is due to the fact that the capacitance 

 C22 varies as l/xo whereas the coupling coefficient of the stream to the gap 

 decreases more slowly at first than the capacitance so that the ratio 

 y\\lCii improves as the spacing becomes moderately wide. The opti- 

 mum ^2 corresponds to an optimum value of Xi which of course depends 

 upon the plate voltage and frequency of operation. For the 1553 at 250 

 volts and 4000 Mc/s, the optimum output spacing is .022". 



