1.1.4 Microwave Transmitter The microwave transmitter includes RF amplifiers, waveguides, power distribution systems, phase control systems, thermal control systems, and structure. It may also include microwave optics such as a lens or reflector. Major components of the microwave transmitter are described below. 1.1.4.1 RF Amplifiers Two RF amplifiers, a klystron and a magnetron, were redesigned for minimal use of non-lunar material. The magnetron was found to contain more non- lunar material, but its higher efficiency reduces the size of the power conversion system. Thus the magnetron is preferred if the power conversion system contains much non-lunar material, and the klystron is preferred if the power conversion system contains little non-lunar material. Using this criterion, the klystron is appropriate for the silicon planar and gallium arsenide concentrator systems; the magnetron is preferred for all others. A third RF amplifier concept, the gyrocon, was dropped from consideration due to its low state of development. 1.1.4.2 Waveguides The waveguide designed by General Dynamics(3), which has a conductive coating of aluminum in a foamed glass waveguide, was selected. It uses no non-lunar materials and remains within the close length tolerance over a wide temperature range. The alternative, an all-aluminum waveguide, could not maintain the required length in the severe thermal environment of the microwave transmitter. 1.1.4.3 Microwave Lens A microwave lens design was developed so that SPS systems smaller than 2 GW could be economical. The lens is a Fresnel lens made of layers of aluminum wire mesh, and requires very little non-lunar material. Assuming that a reasonable design limit is that the lens constitutes no more than 50* of the SPS mass, then a power level as low as 200 MW can be achieved. Further study is required to verify the effectiveness of the lens design.
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