A Microwave F.M. Noise Measuring System with a Simplified Calibration Procedure

The f.m. noise of a microwave oscillator is discriminated with the combination of a circulator and a high-Q reflection type cavity and detected in a balanced mixer. The L.O.-signal for the mixer is also derived from the oscillator under test. The resonator can be frequency modulated with a small ferrite insert. With a constant current input to the ferrite coil, the frequency deviation is flat for modulation frequencies up to 600 kHz and over a 10% microwave frequency range. The frequency modulation capability of the resonator is used for an automatic calibration of the f.m. noise of the microwave oscillator under test. An experimental prototype of this system operating at X-band has a limiting sensitivity of 0.01 Hz/ ¿Hz above 1 kHz from the carrier frequency.