Design of a Two Stage Ku-Band Power Amplifier Based on GaN-HEMT Technology

This thesis investigates the possibility to design a power amplifier at Ku-band using hybrid design technology. The investigation is based on design, simulation and measurement of a two stage hybrid power amplifier. The device technology used throughout the project is 0.25 um GaN-HEMT obtained from TriQuint Semiconductor. The two stage power amplifier consists of a gain stage and a power stage where balanced topology is employed by means of a 3-dB Branch-Line-Coupler (BLC). The required source and load impedance values are obtained from the source and load pull simulations. The ADS schematic simulation results show that the amplifier delivers 43.2 dBm output power at , 19.2 dB gain and 42 % power added efficiency at 15 GHz. For an input power of 24 dBm, the gain stage delivers 10.9 dB gain while the power stage delivers 8.9 dB gain. The momentum simulations, conducted at 15 GHz, provide 40.4 dBm output power, 12.5 dB gain with 21 % of power added efficiency. After tuning with copper foils, small signal measurements provided 14.09 GHz to be the frequency where the maximum gain is obtained. Large signal measurements were only performed for the fabricated and tuned gain stage of the power amplifier. Large signal measurements, conducted at 14.09 GHz, indicate that the gain stage of the power amplifier provides 4.08 dB maximum gain and more than 13 % drain efficiency. According to the obtained results from both simulations and measurements, Ku-band hybrid power amplifier designs based on GaN-HEMT technology are highly sensitive. This sensitivity is the natural result of the devices instability. Since the GaN-HEMT devices are instable, the required stability network can be complex. Therefore it is essential to maintain the stability network simple with the similar size components. On the other hand, the optimum source and load impedances are highly capacitive. Hence, it makes difficult to design wideband matching networks, which also limits the performance. However, it can be concluded that power amplifier designs at Ku-band based on hybrid technology can provide acceptable performance results