Frequency stability and phase noise performance of X-band to Ka-band active multiplier

The performance of an active frequency doubler used to generate a pump signal for a solid-state microwave amplification by stimulated emission of radiation (MASER) based on paramagnetic impurity ions in sapphire is reported. The frequency doubler has been characterised in terms of phase noise, power dependence and frequency stability (Allan variance) for an output frequency range between 20 and 40 GHz. With the measurement system referenced to a 10 MHz hydrogen MASER, the doubler exhibits a single sideband phase noise of ~-108 dBc/Hz at 1 Hz offset frequency, from which an upper limit fractional frequency instability of about 2 × 10^-16 at 1 s integration time is estimated.