An 8 GHz high power AlGaN/GaN HEMT VCO

A high power X-band hybrid microwave integrated voltage controlled oscillator (VCO) based on AlGaN/GaN HEMT is presented. The oscillator design utilizes a common-gate negative resistance structure with open and short-circuit stub microstrip lines as the main resonator for a high Q factor. The VCO operating at 20 V drain bias and -1.9 V gate bias exhibits an output power of 28 dBm at the center frequency of 8.15 GHz with an efficiency of 21%. Phase noise is estimated to be -85 dBc/Hz at 100 kHz offset and -128 dBc/Hz at 1 MHz offset. The tuning range is more than 50 MHz. The dominating effect of GaN HEMT's flicker noise on oscillator phase noise performance has also been discussed. The measured results show great promise for AlGaN/GaN HEMT technology to be used in high power and low phase noise microwave source applications.