Date of Award


Document Type

Open Access Thesis


Electrical Engineering

First Advisor

Grigory Simin


Microwave switches are important components which have been widely used in many microwave systems, such as electronic products, satellites communications, antennas, and radars etc. Traditionally, microwave switches are fabricated using pin diodes or MEMS, Si MOSFETs or GaAs HEMTs. These devices, due to the material limitations are suffering from a low breakdown voltage and are unable to handle high power. III-Nitride based varactor microwave switches provide opportunities for high power microwave devices, due to highly conducting 2D electron gas in the channel and high breakdown electric field.

Designing microwave switches typically involves modeling and simulation using tools such as MATLAB, ADS etc, to save the designing time and cost. However, these tools are not sufficient for precise simulation of low-loss microwave switches, where even minor scattering and loss in waveguides incorporating the device, may have significant effect on the overall switch performance.

In this thesis, HFSS electromagnetic simulation method is introduced to simulate microwave switches using GaN HFETs and varactors. First, the HFET and varactor models for HFSS has been developed and validated. Then various types of microwave switches with operating frequency above 10GHz have been simulated and optimized. Specific emphasis is made on a novel capacitively coupled contacts (C3) varactor, not requiring ohmic contacts and gate electrodes. Using HFSS, this thesis demonstrated

several modified C3 switch structures, achieving resonance in the operating frequency range thus greatly increasing the isolation, up to 42dB at 22GHz.