RECTENNA SYSTEM DESIGN W. C. Brown - Raytheon Company R. M. Dickinson - NASA/JPL E. J. Nai os - Boeing Aerospace Company J. H. Ott - Novar Electronics Corporation The function of the rectenna in the solar power satellite system is to convert the downcoming microwave power beam to electrical grid power. Due to its large physical size (a typical rectenna site is a 10 KM x 14 KM ellipse) and element composition (over 10$ diode assemblies), the projected cost savings of automatic mass production are of prime importance. The fundamental processes at the rectenna consist of rectifying the incident r.f. field into d.c. current using Schottky barrier diodes, filtering the rectified output, combining it and processing it to higher voltages for distribution. Hierarchial combination and processing of currents is done several times to integrate the relatively low power per diode to electrical grid power magnitudes. Figure 1 illustrates the basic design choices based on the desired microwave field concentration and ground clearance requirements. The current design utilizes a non-concentrating inclined planar panel with a 2 meter minimum clearance. The receiving element options are summarized in Figure 2. Dipoles in various implementations represent the most straightforward way of receiving a linearly polarized incident field compatible with the slotted waveguide transmitting array. The modified half-wave dipole in Figure 2 has been selected in the baseline. Higher gain per element options, however, are worthy of further study. The baselined modified half-wave dipole, with a capture area of 70 CM^ (typical) will provide between 1-2 watts of power per diode at the center of the rectenna (23 mW/CM^) indicating good efficiency. Dipole arrays are used near the rectenna periphery to maintain rectification efficiency. The design chosen integrates the dipoles and their associated power and microwave circuitry inside an aluminum environmental shield and support structure which readily lend themselves to mass production methods. The dipole assembly also contains a filtering and matching circuit. The number of dipoles in the rectenna is approximately 1.3 x 10'0. To effectively match the incident power flux to the diode rectifiers, a ten ring design has been adopted (Figure 3). Antenna elements are formed by using the basic dipoles in arrays containing 2, 4, or 8 dipoles. The array assemblies are combined into 7,060,224 panels, each 3M x 3.33M, which are the smallest assembly units from the fabrication point of view. There are four different types of panels, corresponding to the four different types of receiving arrays. Units are combined from panels in such a manner that nominally 1,000 panels are in one unit. The last assembly which is formed at DC is called "group" (5-10 MW of power). The DC to AC inverters are located at the group centers with 70 MW of power, typically. The rectenna AC system is shown in Figure 4. The 40 MW converter station output is transmitted by underground cable to 200 MW transformer stations where the voltage is stepped up to 230 kV, then collected in 1,000 MW groups and transformed to 500 kV for interphase with the bulk transmission system. The switchyards are shown arranged as reliable "breaker and a half" schemes where single contingency outages may be sustained without loss of power output capability. Availability calculations for the baseline rectenna design indicate that 80% of the rated satellite power is available 96.8% of the time, and that scheduled no-power periods total only 208 hours per year. For
RkJQdWJsaXNoZXIy MTU5NjU0Mg==