The Ka-Band Communication Systems of the Lincoln Experimental Satellites LES-8 and LES-9

Abstract

Introduction L INCOLN Experimental Satellites LES-8 and LES-9 are a pair of experimental communication satellites designed and built to operate in a synchronous ecliptic orbit and to communicate on a crosslink from satellite to satellite as well as with surface terminals. At synchronous-orbit altitude, each satellite has a groundvisibility area about 8000 miles in diameter. With crosslink communication between two satellites spaced thousands of miles apart, a single pair of satellites could provide communications among terminals anywhere in an area covering more than 3/4 of the surface of the Earth. Communication links are possible at both UHF and Ka-band at approximately 37 GHz. Figure 1 shows a cutaway drawing of LES-9. The side facing the Earth is the forward platform, which is used for mounting and precision alignment of the Ka-band antennas and the Earth sensors. The Ka-band receiver diplexer filters and front ends are mounted as close as possible to the diplexer polarizer mounted on each antenna. The Ka-band transmitter power amplifiers are mounted on sections of the internal decagon adjacent to the forward platform to minimize the length of the waveguide runs to the antennas. LES-8 and LES-9 each utilize two independent Ka-band communication systems (see Fig. 2). The Ka-dish system uses a fixed paraboloidal reflector in conjunction with a steerable flat reflector to provide a narrow beam, tracking antenna for crosslink or uplink/downlink communications. The Ka-horn system includes a fixed horn to provide a wide-beam antenna coverage. Local oscillator requirements for both systems are provided by a single Ka-band local oscillator. Each receiver subsystem features a broadband low-noise mixer utilizing Schottky-barrier diodes to achieve a typical system noise figure of less than 8 dB. Each transmitter includes an array of solid-state amplifiers which utilize IMPATT diodes, and delivers 0.5 W of power to the antenna. The transmitter signal is modulated at a lower frequency and is upconverted to Kaband using a mixer similar to that used in the low-noise receiver. This paper will discuss the Ka-band systems carried on LES8 and LES-9, which were built to demonstrate component and