Monolithic grid amplifiers

Author: Liu, Cheh-Ming Jeff

Year: 1996

Degree: Dissertation (Ph.D.)

Advisor: Rutledge, David B.

Committee Member: Unknown, Unknown

Option: Electrical Engineering

DOI: 10.7907/9c1y-j677

Abstract

A grid amplifier is a quasi-optical power-combining device which amplifies a microwave beam and spatially combines the outputs of many transistors, making it possible to greatly increase power. This thesis will discuss gain and stability models for Heterojunction-Bipolar-Transistor (HBT) grid amplifiers. A transmission-line equivalent-circuit model for gain analysis will be discussed. Hybrid HBT grid amplifiers, fabricated with high-dielectric substrates, have been demonstrated with gains of 11 dB at 10 GHz and 6 dB at 16 GHz. A stability model for common-mode oscillations will be presented and stabilizing techniques will be discussed. With stabilizing capacitors, a highly stable grid amplifier has been achieved at 10 GHz. Based on the models, a 36-element monolithic HBT grid amplifier is designed, fabricated and tested. The result is a highly stable monolithic grid amplifier with a peak gain of 5 dB and 3-dB bandwidth of 1.8 GHz. This monolithic HBT grid amplifier has a maximum saturated output power of 670 mW at 40 GHz. The far-field approach was employed to measure the gain and power of the grid amplifiers. Theoretical discussions on aperture efficiencies of grids and thermal modelling for a two-layer structure of a grid with a carrier will be discussed.

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