| As the development of mobile and satellite communication system, in order to obtain higher data transfer rate, signals have large peak-to-average power ratios (PAPRs), as contains multichannel subcarriers with variable phase and amplitude. Higher efficiency and linearity power amplifier is required for the signals with high PAPRs. Doherty power amplifier (DPA) has been widely used because of relatively simple realization and obvious efficiency improvement. GaN high electron mobility transistors (HEMTs) have attracted great attention because of the outstanding material properties and an excellent trade-of between output power and efficiency, the research of the DPA based on GaN devices has become a hotspot.In this paper an S-band power amplifier was designed by using a three-stage cascade structure. To achieve this design goal, GaN device of high gain and efficiency were chosen for the driving amplifier, DPA structure based on GaN device was designed for the last stage amplifier. Combining with the domestic and foreign researches and RF simulation software ADS, did some simulation and research about the DPA and the relationship between various parameters, summarized series of solutions such as the offset line for main and peak amplifier, suitable gate voltage and uneven power splitting in favor of the peak amplifier to solute the drawbacks. Finally realize the design of the S-band power amplifier’s layout, structure and power protection by rational layout and simulation.In the actual test, the DPA implement a small signal gain of13dB, a saturation output power of47.22dBm when the PAE was67.08%and the gain was11.7dB. The PAE was56.74%up to3dB of back off, or44.3%up to6dB of back off.The total power amplifier exhibited a saturation output power of47.22dBm and a gain of43dB, also achieved a power added efficiency (PAE) of64%; the power added efficiency is higher than38%up to a6dB back off. The entire design meets the requirements from the test results. |
