Design of a GaN HEMT High Efficiency High Power Frequency Tripler Using a Class-F Technique

The properties of Gallium Nitride HEMT technology allow for higher performance spacecraft RF payloads with lower size, weight and power. In this paper, we present a high efficiency, high output power, low phase noise class-F frequency tripler utilizing a GaN HEMT device. This frequency tripler converts a 750MHz input frequency into a 2.25 GHz output frequency. This paper applies the class-F design technique, conventionally used for high efficiency power amplifiers, to the design of frequency multipliers. An active harmonic load-pull system was built and utilized to explore the desirable harmonic load impedances presented to the GaN HEMT device, to achieve class-F operation for optimal RF/DC power efficiency. The results obtained from active load-pull tests show that the load network of the tripler should aim to achieve impedance match for the 3rd harmonic, while simultaneously maintaining an open for other odd harmonics and a short for even harmonics. Consequently, the drain voltage waveform is shaped as a square wave, and the drain current waveform is shaped as a half-sine wave at the 3rd harmonic. Based on the class-F harmonic tuning approach described above, a class-F frequency tripler was fabricated using a Cree CGH40006 GaN HEMT. Hardware measurements demonstrate that the tripler features a PAE of 23%, an unprecedented output power of 29.4 dBm, and a conversion gain of 8.1 dB. The designed tripler provides a minimum harmonic rejection of 7.3 dB at the fundamental frequency. The rejection at the higher order harmonics were all greater than 30dB. In addition, residual phase noise was measured to be less than -146 dBc/Hz at 10KHz.