Efficient and linear microwave transmitters for high peak-to-average ratio signals

Current wireless communication systems use spectrally efficient modulation of microwave-frequency carriers (e.g. W-CDMA, OFDM). The base-station downlink signal is characterized by high peak-to-average power ratio (PAR) and a Rayleigh amplitude distribution and requires highly linear microwave transmitters. Traditional power amplifiers (PAs) can have high efficiency near peak output power and, as a result, have low average efficiencies for high-PAR signals. This thesis addresses the challenge of maintaining linearity and high efficiency over a broad output power range in high-power microwave communication transmitters.;PA efficiency is addressed with an improved load pull characterization method for high-power transistors in the 2-GHz range, in which fundamental frequency load pull is extended to include harmonic impedance termination and full-wave electromagnetic discontinuity analysis. The method is validated for harmonic-tuned and switched-mode high-efficiency PA topologies reaching 81% efficiency at 2.14GHz with 36W peak output power and 14.5 dB gain from a class-F--1 prototype.;The high-efficiency operation is extended to reduced output power levels using an envelope tracking (ET) transmitter architecture implementing both drain and drive modulation. Drain modulation is achieved using an analog dynamic supply designed in close collaboration with colleagues in analog and power electronics. A variety of signal processing techniques (e.g. digital pre-distortion) addressing specific distortion mechanisms are used to fully restore transmitter linearity. A methodology for system design and integration is developed which relies on a new measurement-based ET system simulation tool. The simulation merges aspects of digital baseband, signal processing, digital-to-analog conversion, up-conversion, envelope-bandwidth analog circuits, and RF components.;The integrated ET demonstration transmitter measures 50.6% total system PAE with over 7 dB adjacent channel power linearity margin for a 40-W peak power 7 dB PAR W-CDMA downlink signal at 2.14 GHz. The ET transmitter dissipates 61% less total heat than the standard drive-modulated solution, operating more than 74% longer from an equivalent fixed energy supply, while exceeding W-CDMA 3GPP linearity specifications.