Three 10W C-band Power Amplifier Alternatives for use in TT&C-Transmitters
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This thesis describes the first stage in designing and realizing three 10W C-band power amplifier alternatives based on the GaN-technology for use in Kongsberg Norspace future TT&C-transmitters. The operational frequency range spanned from 3.4GHz to 4.25GHz. It was decided to build one single-stage amplifier based on the 10W CGH40010F transistor from Cree and two dual-stage amplifiers with a balanced second stage based on the 6W CGH40006P transistor, from the same manufacturer. AWilkinson power divider was used to feed each branch in the second stage. In the design procedure, source and load pull simulations were performed in order to retrieve the optimal impedances for each transistor and as a basis for the design of the matching networks. By utilizing a looping method in the design process of the matching networks, it was possible to obtain results that, to some extent, fulfilled the requirements. Simulations and design were carried out in ADS by Keysight (former Agilent). The simulated results showed that all three designs were capable of delivering 10W output power throughout the frequency band. The single-stage amplifier obtained a simulated power added efficiency (PAE) above 45% at 40dBm output power, while the two dual-stage designs achieved a PAE between 41-44% and 34-36%, respectively. S-parameter simulations reviled that the single-stage design accomplished a small signal gain of 11.3dB-11.7dB, while the input reflection coefficients varied between -3dB and -5dB. To achieve the requirement of having the input reflection coefficients less than -10dB, the dual-stage designs utilized an attenuator with 1.5dB loss at the input match, both designs obtained a small signal gain above 20dB. Like the simulated results, the large signal measurements showed that the amplifiers were capable of delivering 10W output power, except the single-stage design at 4.0375GHz (which were one of the test frequencies). The measured power added efficiency for the single-stage amplifier varied between 27%-44%, while the two dual-stage amplifiers obtained a PAE between 39-43% and 35-42%, respectively. This implied that non of the designs managed to fulfill the requirement of having a total power consumption less than 25W over the specified frequency range. A simulated large signal stability analysis were performed on each design and the results revealed that one of the dual-stage designs had a potential instability around 790MHz, and practical spectrum measurements confirmed frequency components at 750MHz, 1.51GHz and 2.25GHz. However, the spurious frequency components had no measurable impact on the performance. A small section presenting the future prospects in terms of utilizing the GaN-technology in Space and suggestions for future work, have also been included. The thesis concluded that several iterations must be done before an integration with the transmitter can be made.