A Low Phase Noise Oscillator Employing Weakly Coupled Cavities Using SISL Technology

A Ku-band low-phase noise oscillator, using a weakly coupled cavities resonator (WCCR), is proposed based on substrate-integrated suspended line (SISL) technology. Different from using a bandpass filter as the frequency selector for the feedback oscillator, we use weak coupling between resonators to form a resonator with a higher
$Q$
. The theoretical analysis of weak coupling is derived. Under weak coupling, the equivalent
$Q$
and insertion loss of the WCCR is given based on the mathematical deduction. The proposed WCCR can double the
$Q$
factor of the single cavity resonator (SCR) at the expense of an increase in the insertion loss. Two oscillators using WCCR and SCR are designed and fabricated to verify the theoretical analysis. The measured results show that the loaded
$Q$
of WCCR increases by 80% compared with the SCR. The proposed oscillator has a low measured phase noise of −137.36 dBc/Hz at 1 MHz offset from the carrier frequency of 12.355 GHz, and the FOM is −207.12 dBc/Hz. Compared with the oscillator using SCR, the measured phase noise is improved by 5.13 dB. Moreover, the proposed oscillator based on SISL technology has the advantages of low cost, compact size, and self-packaging properties.