Oscillator noise measurements at millimetre wave-lengths

To achieve the high sensitivity with FM noise measurements, a key requirement is to have a low loss frequency discriminator with as large a discriminator slope as possible. The measurement technique used in this system uses a very high Q quasi-optical cavity in reflection which gives an extremely high discriminator slope. Typical values for the loaded Q are in excess of 100000 with almost zero insertion loss, which is over an order of magnitude better than that previously achieved with waveguide cavities. (An increase in Q by a factor of 10 can be expected to decrease the noise floor by a factor of 20 dB). Compared to delay line techniques at this frequency, the improvement in sensitivity can be better than 40 dB. This technique allows very high sensitivity at low input power over an ultra wideband frequency range.<>