Frequency-tunable high-efficiency power oscillator using GaN HEMT

In this paper, a frequency tunable, high-efficiency power oscillator using Gallium Nitride High Electron Mobility Transistor (GaN HEMT) for the RF power source applications is designed and fabricated. The steady state oscillation occurs in a delay line feedback loop which length is adjusted to tune oscillation frequency. A harmonic-tuned matching network technique is employed to obtain high conversion efficiency characteristic of the oscillator. The measured output power and conversion efficiency of the fabricated oscillator are 44.63±0.2 dBm and better than 62%, respectively, across the 890-950 MHz band with a drain bias voltage of 40 V. Then a hair-pin resonator is designed and employed into the oscillator in order to improve phase noise characteristics and frequency selectivity. The experimental results of the oscillator with the hair-pin resonator exhibit the output power of 43.55 dBm, corresponding to the conversion efficiency of 61% at 920 MHz. The measured phase noise characteristics are -64 dBc/Hz and -81.24 dBc/Hz at 10 kHz offset without and with the hair-pin resonator, respectively.