Microwave Dielectric Resonator Discriminator Oscillator

A new method (**) to improve the phase noise near the carrier of microwave frequency sources, particularly suitable for Low Capacity Digital Radio (LCDR) systems, is here presented. This is obtained including in a DRO a frequency discriminator, realized by means of the same oscillator cavity. The transmitted and reflected waves of the cavity are measured, combined and detected by a couple of diodes with low 1/f noise. These signals are compared in a differential amplifier that drives a varactor phase-shifter set between the active device and the cavity. In this way the reflection coefficient phase of the active device can be changed in order to correct its phase transients. As a result, lower the 1/f noise of the diodes with respect to the 1/f noise of the active device, greater the reduction of the oscillator phase noise. This technique applied to a microwave DRO may replace the synthesizer architecture achieving the same performance with lower circuit complexity, greater hardware compactness and lower cost.