Several complications arise in applying the “Magic T” to the SPS application. A set of sensors is needed to sense reflected power at the rf input and feedback control loops are needed to minimize the reflected power. The sensors would be required to function at high temperature. At the same time the output of the “Magic T" now sensed at the slotted wave guide radiator needs to track phase and amplitude references. There are also special problems in starting to assure simultaneous operation in both tubes and a rapid balancing of phase and amplitude of the individual tube outputs. Although it may be possible, it does not seem reasonable to rely upon matched tubes for phase balancing at the output terminal of the Magic T, and it certainly would be necessary to have buck boost coils on each tube for amplitude control. The problem appears to be too complicated to be solved simply, and further study seems necessary. Now, four years later, there is an apparent sound solution to this problem. As is often the situation, the solution came indirectly from inspiration and insight derived from another source of activity. In this case, it was a study effort for an Earth-based microwave power transmitter for a high-altitude, microwave-powered balloon or airplane, driven by the need for a very low cost radiating element (3). In this transmitter concept, each radiating element in the form of a slotted waveguide radiator about 30" square had to be driven from a low power reference microwave source flowing through a low power digital phase shifter, as shown in Fig. 3. The phase of the output of the high power microwave generator had to be in step with the phase of the drive signal. This was accomplished by comparing the phases of the input and output microwave power and using the difference to change the current in
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