Developments in power amplifier module and comparison of circulators for solid-state microwave ovens.
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The solid-state microwave ovens (SSMO) use solid-state power amplifiers for heating food inside the oven cavity. These cooking devices are intelligent systems that can change RF signal characteristics in terms of power, frequency and signal phase. The solid-state transistors are rugged, smaller and cheaper than magnetrons. The SSMO is one step forward towards replacing the vacuum tube (magnetron) technology in heating applications such as microwave ovens. This thesis presents the work done in the developments of power amplifier (PA) module designed for SSMO system. The PA module operates in industrial, scientific, and medical (ISM) band at 2:45 GHz with 250 W output power. Four PA modules are utilized in the SSMO system for multi-channel delivery of RF power into the oven cavity. The key achievements of this thesis are the analysis of faulty PA modules, characterization of RF power detector, and comparison of circulators. Burnouts were observed in several 1st generation PA modules. Failure analysis is made to thoroughly investigate the problem, and to find an enduring solution. RF power detector is developed to avoid burnouts in the future. The power detector monitors the flow of RF power from PA module to oven cavity. It gives the feedback to SSMO system in terms of forward and reflected RF powers. Moreover, five commercial circulators from five different suppliers are compared on identical test-fixtures. The comparison is based on electrical and thermal performance of each circulator as in test cases devised from the operation of the SSMO system.