764 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1953 



based on the oscillographic display of reflected power. The advantage of 

 a flat-topped mode shape for this measurement may be seen by com- 

 parison ^vith the oscillogram of Fig. 22(c) which was obtained for the 

 same resonator under test using a conventional reflex klystron as swept 

 frequency source. 



The center frequency of the flat power band obtainable with the 

 coupled resonator reflex klystron may be shifted into the intermediate 

 frequency range by mixing its output with a suitable local oscillator. 

 This is shown in Fig. 23 where the first three oscillograms represent a 

 power band flat to within =b0.1 db and 60 mc wide centered around an 

 IF frequency of 70 mc. The frequency markers are obtained from a 

 signal generator tuned to the frequencies indicated and coupled lightly 

 to the output of the mixer. Fig. 23(b) shows the gain-frequency char- 

 acteristic of a 70 mc-IF strip having a useful bandwidth of 22 mc. The 

 last oscillogram shows the gain-frequency characteristic of the same IF 

 amplifier with the coupled resonator reflex klystron replaced by one of 

 conventional design. Due to the inadequate electronic tuning range of 

 this klystron and due to the asymmetry of its mode shape, the gain 

 envelope of the IF amplifier appears distorted. 



6.0 CONCLUSIONS 



The theory and reduction to practice of a coupled resonator reflex 

 klystron have been presented. This device differs from the conventional 

 reflex klystron in that the electronic admittance interacts with the input 

 admittance of two coupled resonators. Significant and advantageous 

 changes in performance resulting therefrom are: 



(1) Power output can be made to be substantially flat over part of 

 the electronic tuning range. The frequency range of flat power is greater 

 than the half power electronic tuning range of a klystron having the 

 same electron-optical system but interacting with a single resonator. 



(2) The half -power electronic tuning range of the coupled resonator 

 klystron is more than twice that of the equivalent single resonator 

 klystron. 



(3) Modulation linearity may be obtained over a greatly increased 

 frequency swing. 



A reduction in power output of about 3 db occurs for a secondary 

 resonator Q and coupling coefficient adjustment designed to yield a 

 maximum flat band or maximum electronic tuning, a much smaller 

 reduction in output power, perhaps 10 per cent, will provide a substantial 

 improvement in modulation linearity. 



