On-chip GaN-on-SiC VCO using a tunable substrate integrated waveguide loaded with complementary split ring resonator

This paper presents an S-band voltage-controlled oscillator (VCO) using a tunable half-mode substrate integrated waveguide (HMSIW) loaded with complementary split ring resonator (CSRR) in GaN-on-SiC high-electron-mobility transistor technology. A varactor connected to the center of the outer conductor of the HMSIW-CSRR changed the effective capacitance, resulting in a resonance frequency shift but a fixed transmission zero. Therefore, the S-band VCO can be tuned by the HMSIW-CSRR using harmonic suppression. The tunable HMSIW-CSRR VCO exhibited a frequency tuning range of 3.55–3.98 GHz with a varactor voltage of 0–6 V. The maximum output power was 21.1 dBm and rf-to-dc efficiency was 12.8% at 3.98 GHz. The lowest phase noise was −117 dBc/Hz with 1-MHz offset at a 3.56 GHz carrier frequency with 30.55 dBc of harmonic suppression.