DESIGN AND DEVELOPMENT OF AN ADVANCED MICROWAVE POWER LEVELING LOOP

Abstract

An advanced microwave power leveling loop (MPLL) was conceived, designed, fabricated, tested, and used during spacecraft in-orbit testing. The primary function of the MPLL is to maintain constant RF power transmitted from an earth station antenna during spacecraft in-orbit transponder testing. The MPLL utilizes nonlinear analog electronics with flexible signal path routing under microprocessor control. It achieves a power control dynamic range of greater than 50 dB with better than 0.1 dB of control resolution. Power level step changes of 20 dB can be accomplished in under 10 ms. The MPLL is IEEE-488 bus controllable and is designed for use in automated in-orbit test systems to facilitate the measurement process and produce more repeatable results than have previously been possible. Measurements performed with the aid of the MPLL include transponder frequency response, group delay, gain, and saturation level. The system can also be operated in a manual mode, and utilizes state-ofthe-art human interfacing techniques such as a display/entry panel and a rotary encoder control knob. This paper describes the MPLL design process, including computer simulation work and breadboard testing. Performance and temperature chamber test results are presented for breadboard and manufactured units.