Ultralow-Phase-Noise Microstrip Oscillator Based on Quasi-Bandpass Frequency Selection Network With Multiple Transmission Zeros

This article proposes a microstrip feedback-type oscillator incorporating a novel quasi-bandpass frequency selection network (FSN) for low phase noise (PN) operation. Through introducing direct source/load coupling between two coupled quarter-wavelength resonators, the FSN can theoretically realize a canonical second-order general Chebyshev bandpass response with two transmission zeros. Furthermore, the feedlines with short-circuited ends are specifically designed to generate more transmission zeros. Accordingly, this FSN is featured by quasi- bandpass response with multiple transmission zeros, so that high group delay and good out-of-band performance are achieved. Such feature plays an important role in the oscillator performance. As demonstration, one oscillator example was fabricated and measured. Its operating frequency is 1.98 GHz, the PN is −129.85 dBc/Hz at 100 kHz, the output power is 9.61 dBm, and the second harmonic suppression (SHS) reaches 48.21 dBc. All these indexes outperform those of all the other oscillators, and our reported PN is the lowest one in S-band up to now.