Design of microwave oscillator and voltage-controlled oscillator with second and third harmonic suppressions

In the paper, a microwave oscillator and a voltage-controlled oscillator (VCO) are developed using the compact T-equivalent ring resonator and a wideband harmonic suppressed network. The compact T-equivalent ring resonator has a wide stopband to suppress the 2^nd and 3^rd harmonic of the oscillator. It also takes the advantage of easy extension to a tunable resonator, and then applies to implement a VCO. The harmonic suppressed network is added at the output of the oscillator to enhance the suppression performance. The oscillator is designed at 2.318 GHz. The measured phase noise are -104.15 dBc/Hz and -124.9 dBc/Hz at 100 KHz and 1 MHz offset frequency, respectively. The measured 2^nd and 3^rd harmonic suppression of the developed oscillator are -63.08 dBc and -60.4 dBc, respectively. On the other hand, the developed VCO has a frequency tuning range of 2.184 to 2.355 GHz, and the measured phase noises are from -118.6 to -129.2 dBc/Hz at 1 MHz offset frequencies. In the frequency range of 2.285 to 2.355 GHz, the measured 2^nd and 3^rd harmonic suppressions are better than -70 dBc and -60 dBc, respectively.