Abstract: An IQ mixer is used in a Pound-stabilized microwave source to detect amplitude modulation of the signal reflected from the reference resonator. By properly configuring the IQ mixer so that the LO and RF inputs are maintained in quadrature at the Q mixer, hence in-phase at the I mixer, lower levels of amplitude modulation may be detected at lower modulation frequencies compatible with optimal choices of resonator coupling and maximal phase to amplitude conversion.

Abstract: An IQ mixer is used in a Pound-stabilized microwave source to detect amplitude modulation of the signal reflected from the reference resonator. By properly configuring the IQ mixer so that the LO and RF inputs are maintained in quadrature at the Q mixer, hence in-phase at the I mixer, lower levels of amplitude modulation may be detected at lower modulation frequencies compatible with optimal choices of resonator coupling and maximal phase to amplitude conversion. With the Q mixer held in quadrature it acts as a broadband phase noise detector. A portion of the Q mixer output is bandpass filtered and summed with the I mixer Pound-server voltage to achieve both center frequency stabilization and broadband phase noise suppression.

Abstract: A fixed-geometry probe for exchanging microwave energy with a cavity resonator is easy to manufacture, reliable and readily adjustable external to the cavity to select a coupling coefficient. The probe includes a transmission line that enters, turns and exits the cavity resonator. A first end of the transmission line lies outside the cavity resonator for connection to a microwave circuit to exchange microwave energy. A portion of the transmission line's outer conductor(s) is removed within the cavity resonator to form a fixed-geometry radiating element to exchange microwave energy with the cavity resonator in accordance with the coupling coefficient. The line's outer conductor is connected to the cavity resonator on either side of the radiating element. A second end of the transmission line is terminated outside the cavity resonator with a terminating impedance creating a mismatch with the line's characteristic impedance to create a reflective stub.