Development and Implementation of a VHF High Power Amplifier for the Multi-Channel Coherent Radar Depth Sounder/Imager System

Abstract

This thesis presents the implementation and characterization of a VHF high power amplifier developed for the Multi-channel Coherent Radar Depth Sounder/Imager (MCoRDS/I) system. MCoRDS/I is used to collect data on the thickness and basal topography of polar ice sheets, ice sheet margins, and fast-flowing glaciers from airborne platforms. Previous surveys have indicated that higher transmit power is needed to improve the performance of the radar, particularly when flying over challenging areas. The VHF high power amplifier system presented here consists of a 50-W driver amplifier and a 1-kW output stage operating in Class C. Its performance was characterized and optimized to obtain the best tradeoff between linearity, output power, efficiency, and conducted and radiated noise. A waveform pre-distortion technique to correct for gain variations (dependent on input power and operating frequency) was demonstrated using digital techniques. The amplifier system is a modular unit that can be expanded to handle a larger number of transmit channels as needed for future applications. The system can support sequential transmit/receive operations on a single antenna by using a high-power circulator and a duplexer circuit composed of two 90° hybrid couplers and anti-parallel diodes. The duplexer is advantageous over switches based on PIN-diodes due to the moderately high power handling capability and fast switching time. The system presented here is also smaller and lighter than previous implementations with comparable output power levels.