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Title: Broadband microwave push-pull power amplifiers
Author: Smith, Robert Martin
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2013
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The research work presented in this thesis aims to achieve high-power, high-efficiency amplification across substantial bandwidths at microwave frequencies. The push-pull topology was identified as a promising possible solution which had previously not been considered for this application. The key component in the push-pull power amplifier is the balun, which converts between balanced and unbalanced signal environments. The novel use of ferrite materials allowed the half-wavelength resonance of a coaxial-cable transmission line balun to be suppressed, greatly extending its bandwidth. This was done by utilising the resistive properties of the ferrite material at frequencies greater than 1 GHz, at which these materials are not usually studied. The multi-decade performance of the transmission line baluns opened up the possibil- ity of realising push-pull power amplifiers across similar bandwidths. The measurement of these baluns revealed that they present a resistive impedance to the odd-harmonic frequencies, and an open circuit to the even-harmonic frequencies. This is a significant departure from the conventional view of the push-pull mode, and led to the modes of operation inside a microwave push-pull power amplifier being reconsidered. Factorised waveform expressions were used to describe the new modes of operation, and these were verified through load-pull simulations and measurements. The wave- forms were found to resemble the inverted modes of operation, with similar desirable characteristics such as high efficiency and an increase in output power compared to Class A. The viability of the push-pull amplifier topology was demonstrated through two pro- totype amplifiers, which achieved high output power levels and efficiencies over multi- octave bandwidths. Measurement systems for characterising and analysing these amplifiers were developed, which should lead to improved understanding and better performance in future.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering