RF and microwave power amplifier designs based on novel power dividing/combining techniques.

Abstract

With the rapid advancements of the military and commercial communications systems, the demands for high power solid-state power amplifiers with high efficiency and low cost have greatly increased. Because of the limited output power from single solid-state device, combining the power from multiple devices to achieve higher power levels is inevitable, especially in the design of microwave and millimeter-wave power amplifiers. The primary objective of this research is to develop high efficiency and compact power combining circuits for high power multiple-device power amplifier designs. Four power combining techniques have been proposed for different power amplifier applications at RF and microwave frequencies. First, two Ka-band eight-device power combining amplifiers based on the slotted-waveguide power dividing/combining circuits are presented: a resonant design for narrowband power combining and a traveling-wave design for broadband power combining. The resonant slotted-waveguide power amplifier provides 31.6 dBm (1.45 W) output power at 1-dB gain compression (P_{out 1dB}) with a power combining efficiency (PCE) of 72% at 33 GHz and the measured 3-dB bandwidth of 3.8%. In the traveling-wave power amplifier, both of the power combining efficiency (PCE) and the 3-dB small signal bandwidth have improved to 80% and 3.2 GHz respectively. The measured P_{out 1dB} for the traveling-wave power amplifier is 33 Min (2 W) at 32 GHz. Besides the advantages of having low profiles and high combining efficiencies, both of the proposed slotted-waveguide power-combining circuits have the capability of efficiently heat-sinking active devices. These designs are also tolerant to device failures. In the second part of this thesis, two multiple-device power-combining amplifiers have been developed based on an extended-resonance power combining technique. In the class-B push-pull power amplifier design, the differential operation and equal power dividing/combining have been realized. Thereby, not only the resulting layout of the power amplifier is simple and compact, but also a high PCE of 93% has been achieved. The class-B push-pull power amplifier has exhibited a 30 dBm P_{out 1dB} at 1.8 GHz with a power added efficiency of 59%. A novel broadband power dividing/combining circuit synthesis approach has been developed to design a 4-device broadband power amplifier. A power combining efficiency of 90% has been obtained between 5 to 9 GHz. The measured P_{out 1dB} of the 4-device power amplifier is 31.9 dBm (1.6 W) at the 7 GHz with 1-dB large signal bandwidth of 5 GHz. The compact layouts of both power amplifiers make them suitable for RFIC and MMIC fabrication. The thesis is concluded by summarizing the main contributions and discussing the implications and directions of future work.