A Comparison of Cavities with Integrated High Gain Time-Varying Capacitive and Transistor Based Reflection Amplifiers

Abstract

In an increasingly contested and congested frequency spectrum [1] it is necessary to minimize noise generated throughout radiating systems. One approach to this problem has been through finding design techniques for integrated structures [2], [3]. These procedures reduce noise generated within a system by eliminating the transmission and matching structures needed between components, improving overall system signal-to-noise performance. The work in this thesis specifies a design technique which integrates an active circuit into a resonator, a fundamental building block for many more complex microwave components. This is accomplished through the coupling of a reflection amplifier into a microwave cavity. By presenting a known input impedance, a one-port amplifier is capable of reflecting a signal back into the cavity at a greater magnitude than incident from the generator, eliminating several matching or transmission structures between amplifier, cavity, and other components in a potential system. First, a three port evanescent mode cavity is designed with strong coupling at the first and second port and an arbitrary weak coupling at the third port. Next, a single port reflection amplifier is designed, using both a transistor and varactor based approach, prioritizing the generation of a low bandwidth, low negative resistance response. Then, the structure of the third port of the cavity is adjusted to present an impedance which will allow for high gain to be delivered from the amplifier with stable operation. The finished structure using parametric amplification demonstrates stability with a high gain of 19.99dB and noise figure of 4.3dB.