GBED Recommendations In summary, the GBED program should aim at producing a high efficiency, high power klystron. This tube should then be evaluated carefully for its noise and efficiency characteristics. Phase-locked magnetron development should continue at the device level, with particular emphasis placed on noise reduction and efficiency enhancement. The solid-state amplifier should be developed further with emphasis on research at the device level rather than at the systems level. Work on innovative concepts such as the photoklystron should be encouraged. 6. RADIATING ELEMENTS Materials The principal problem the panel identified in this area is related to materials. Aluminum looks attractive except for its bad thermal expansion characteristics. Work should be initiated to see if there are any manufacturing or design techniques which would ameliorate this to some degree. An estimate should be made of the maximum thermal distortions which can be expected, and these should be fed back into the antenna radiating pattern calculations. Arbitrarily picking a number of 1/4 inch, as was done in the study, does not seem realistic enough. Problems of PR losses should also be addressed early so that potential later snags can be avoided. Whatever manufacturing technique is finally decided upon, low loss must remain one of the fundamental requirements. A set of principles should be developed which can be used to guide the mechanical design. Although low CTE composites were mentioned frequently during the Workshop, there was no evidence presented which would indicate that these materials would in any way be suitable for microwave circuitry on the SPS. Obvious problems which come to mind include outgassing from the epoxies, conductor adhesion problems, and fabrication techniques. At the present time, these materials are a complete unknown, and should not be relied upon too heavily in the SPS design. Multipacting The multipacting problem was mentioned frequently. Although this phenomenon is fairly well understood, there does not seem to be enough data at the present time to be able to predict if it will be a problem in the MPTS radiator. A set of experiments should be defined which will permit reasonable estimation of the extent of the problem in the SPS environment. This includes outgassing tests on the epoxy composite. Testing Many types of tests must be performed on both the power modules and the subarrays before their microwave performance will be known with certainty. In particular, it is important to determine either the radiated power efficiency or the antenna gain. Measurement of either of these to an accuracy of one or two percent is extremely expensive, and perhaps not even feasible. The large size of the subarray means that a very large range must be used for far field testing. There is no existing range that has sufficiently low multi-pathing to allow such accurate measurements.
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