SWITCHED-MODE MICROWAVE CIRCUITS FOR HIGH-EFFICIENCY TRANSMITTERS by MANOJA

Date The final copy of this thesis has been examined by the signatories; and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline iii Thesis directed by Professor Zoya Popovi´c In wireless communications systems, the transmit front-end consumes a large fraction of the total available power. In particular, the power amplifier preceding the antenna can consume more than 50% of the total average power. Therefore, increasing the power amplifier efficiency is essential to extend battery lifetime (e.g. on a satellite or in portable applications) and reduce power lost to heat that leads to thermal degradation of the electronics in the front end. Both these factors are important in reducing the total cost of the system. By integrating efficient power amplifiers in each unit cell of a transmit antenna array, a transmitter front-end may be optimized for efficient amplification and for combining the output of each unit cell in the low-loss medium of free space. In this thesis, traditionally low-frequency switched-mode class-E and-F high-efficiency amplifier circuits have been extended in operation to 10 and 20 GHz with record efficiencies ranging from a 74% efficient power amplifier at 10 GHz to a 42% efficient power doubler at 20.8 GHz. These circuits are designed for integration with antennas in an active array configuration. The design of the 10 GHz class-E power amplifier is a non-conventional integrated circuit-field design well suited for active antenna arrays with small unit-cell size. A smaller unit cell size allows greater packing density in the array, which in turn allows for lower array losses, and therefore higher power combining efficiency. With the proper biasing and RF input to a class-E amplifier, the circuit presented to the output terminals of the MESFET enables high efficiency operation by offsetting the phase of the current relative that to the voltage waveform, thereby minimizing losses. This can be accomplished with an output circuit having a complex output impedance, whose imaginary part is used to adjust the phases of the current and iv the voltage so that the device operates as a switch with minimal losses, while the real part of the impedance is the desired load to which the power is delivered. In this work, both standard 50 Ω loads and radiating (antenna) loads are considered. In the case of the antenna load, the best performance is achieved if the antenna …