is the development of a unified module of power generator and power transmitter. The module, which we may call "autonomous transmitter module", consists of three layers; high efficiency solar cells on one side; transmitting antenna arrays on the other side; and F-class FET power amplifiers in between the solar cell and the antenna planes. The direct connection of the DC output of the solar cells to the FET amplifier of each active antenna element makes it possible to design a much simpler structure not only of the PSS but also of the future SPS. In the SPS Reference System studied by NASA/DOE in 1980 [2], DC electric power generated by the solar cells must be collected by a DC power collecting network in the huge SPS solar paddle. A critical technology of using super-conductor network for the current collection is being considered for the SPS. This DC power collection network is not necessary for the proposed PSS. If this technology is once established then the design of the future SPS would become much simpler and less expensive. Another critical technological problem raised in the SPS Reference System is a mechanical rotary joint which electrically connects the differentially rotating Solar Paddle and the microwave transmitting antenna in vacuum. This is one of the difficult technological point of the SPS. However, the present PSS does not need such a rotary joint because the DC electric power is directly fed to the FET amplifier situating below the Solar Battery Unit. Elements of PSS The PSS is composed of three main sub-system; a power generator system; a microwave amplifier and transmitter system; and a satellite bus system. A schematic illustration of the PSS structure is given in Figure 2. The PSS is a disc-shaped satellite with a large disc with a diameter of 40m. The disc is composed of the autonomous microwave transmitter modules. The PSS is folded at the time of the launch as indicated in Figure 2 and is deployed in space. One side of the disc is the solar-cell array and the other side is the microwave transmitter. The solar-cell side should be controlled to direct to the sun. This sun-oriented attitude control naturally limits the direction of the microwave beam, even though the beam can be steered in fairly wide angles by the active phase array. To increase the scanning range of the beam, we propose, as an option, to attach a reflector of sun light over the solar-cell array surface. The addition of the optional reflector of the sun light enlarges the service area to which the PSS can direct its microwave beam. Autonomous Microwave Transmitter Module A block diagram of the Transmitter Module is shown in Figure 3. The FET power amplifiers are power-supplied by the DC input from the solar-cells and generate 24 GHz microwave. A new scheme retro-directive phase control system is used for the beam control. A pilot signal of one third of the transmitting frequency is used. This simple conjugate phase generator can determine the phase of the transmitted microwave
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