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GAN-HEMT based KU-band RF power amplifier design for SATCOM applications

Polater, Ahmet Mert
As many of today’s wireless applications need, transmitters of satellite communication (SATCOM) applications require one of the vital circuits in microwave world; a unique RF power amplifier, the sub circuit which is located just before the antenna of the transmitter. RF power amplifiers are the circuits used to amplify the low-power RF signals to achieve adequately high-power signals for various applications. Different than the traditional Si transistor-technology based power amplifiers, the main aim of this dissertation is to study gallium nitride (GaN) high electron mobility transistor (HEMT) based Ku-band RF power amplifier design for SATCOM between a missile’s transmitter and a satellite’s receiver. The reason of common usage of GaN transistor technology in RF power amplifier design in the last ten years caused by the emerging need of more linear operation at higher frequencies; i.e. the frequencies used in SATCOM applications. Therefore, a GaN HEMT based RF power amplifier design with 1 Watt (30 dBm) output power working at 14 GHz center frequency has been studied and designed. All performance parameters are explained by simulation results and measurements. Firstly, the design, whose performance parameters have been verified with schematic and electromagnetic (EM) simulations, has been prototyped with printed circuit board (PCB) etching devices such as LPKF. The observations made after prototyping showed that the performance difference between simulation results and measurements caused by the manufacturing and assembly errors. As an example of such undesired errors, “poor grounding” of the main transistor can be given due to lack of filled vias under the transistor. For such high frequency applications, poor grounding can cause a great degradation on the gain. As a result, the observations have proved that the used transistor does not work properly even though the impedance matching appears as successful for this work. Therefore,it has been understood that more sensitive production method should be chosen. Secondly, a professional foundry is preferred for PCB manufacturing and seems that effects of the problems caused by the first method are eliminated or decreased remarkably. In addition, a “rework” process is conducted after manufacturing for fine tuning. Lastly, a comparison table of simulation results with two different manufacturing methods are also exhibited in this study.