It is concluded that the loss of performance from a large number of output converters resulting from the failure of a single klystron when used in the cascaded amplifier arrangement makes this an unsatisfactory operating mode. It is recommended that klystrons only be considered for operation in a parallel fed configuration. Although the amplitron could operate in either arrangement, its relatively low gain per tube (and therefore the higher number of driver stages required) makes it more suitable for the cascade arrangement than for the parallel feed arrangement. 4.3.3 CASCADED AMPLITRON GAIN The amplitron efficiency of concern for the MPTS is the de to rf conversion efficiency, or the power added divided by the high voltage dc input power. The MPTS would have cascaded amplitrons in large quantities as shown in Figure 4-42. By inspection of the cascaded amplifier diagram it is apparent that the total power output of each tube is effectively divided into two parts, the radiated power per tube and the power input to the following stage. By design the power input to the following stage is equal to the of the first stage. Thus, the only RF power available for radiation is the power added, and the array dc to RF conversion efficiency is the ratio of per tube to power input per tube. 4.3.4 AMPLIFIER NOISE Figure 4-43 schematically represents the concepts for determining the output noise of a cascaded amplifier chain. The total noise can be divided into two components, the component appearing at the input and the component due to self generation within the tube, . The magnitude for input noise is obtained by assuming that it is generated from an amplifier with 10 dB noise figure and an input power level of 0. 1 mW. This is indicated by Figure 4-44. From Figure 4-43 the noise output from the tube in amplifier chain is given by: Representative parameters for a ten tube amplifier chain are as follows:
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