amplifier. However, when a Magic T combiner is used, the phase and amplitude of the output of the two magnetrons must be matched within very close limits at the point where they combine at the Magic T output, or else an amount of reflected power too large for a ferrite circulator to handle on the input side will result. Ideally, what is desired is to be able to drive the Magic T on the input side with less than five watts of microwave power and to achieve about eight kilowatts of output from the Magic T and associated magnetrons with a reflection to the input of only a few watts to prevent overheating of the ferrite circulator and the resistive load that absorbs the power. At the time of the conclusion of the study sponsored by the DOE/NASA program, we did not visualize how such high gains could be achieved nor how the phase and amplitude of the power output of the two magnetrons could be balanced at the Magic T output. The nature of the unresolved problem that created a design dilemma at the end of the study may perhaps be better understood by quoting from the final report (2). The following quote should be read with the knowledge that we had been successful in demonstrating phase and amplitude tracking simultaneously in a magnetron directional amplifier that consisted of a single magnetron and a single 3-port ferrite circulator. Such a demonstration had been one of the principle objectives of the study contract. In the interests of demonstrating the general principles of phase and amplitude tracking with the magnetron directional amplifier, the ferrite circulator was used as the passive directional device. While the use of the ferrite circulator for terrestrial use is sound, its use in space may be objectionable because currently available ferrite circulators will not operate in an environment of 300°C. Thus, an investigation needs to be made to see if new or different materials could be used to solve this problem. Because of the potential difficulty with the ferrite circulators in the SPS application, the conventional wisdom has been to use the “Magic T” or its equivalent to perform the same functions with high efficiency and with no need for temperature sensitive materials.
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