GPS Spaceborne High Power/High Efficiency L-Band Sources

The GASFET currently used in the Global Positioning System (GPS) produces 175 Watts at L-Band with an efficiency of 44.3%, weighs 24 pounds and occupies a volume of 410 cubic inches. Because of its high efficiency and power handling capability, the traveling wave tube (TWT) is the amplifier of choice in almost all communications satellite applications. In addition, the failure rate in orbit for solid state power amplifiers is 30% higher than for TWT amplifiers. For these reasons, the recently orbited commercial high power L-Band satellites, XM Radio and Sirius Radio, are powered by TWT’s. We propose to support the GPS application with a TWT driven by a gated emission electron gun that will allow substantial reductions in weight and volume without sacrificing power output and efficiency. The Phase I analysis predicts that the proposed TWT will have an output power of 265 Watts and a gain of 43 dB at L-Band with an estimated efficiency of 60%. This TWT could be utilized in the GPS satellite as a component of a TWT amplifier or as the power amplifier in an L-Band microwave power module (MPM). A similar C-Band MPM weighs 4.2 pounds with a volume of 48 cubic inches.