Abstract: An oscillator includes an amplifier having an input and an output and a feedback circuit disposed between the input and the output of the amplifier. The feedback circuit includes a plurality of resonators and a pair of switches. Each switch includes a first port and multiple connectable ports, the multiple connectable ports of each switch connected to a corresponding one of the plurality of resonators. The feedback circuit further includes a voltage-controlled phase shifter disposed in series with the switches. The oscillator further includes a discriminator circuit, responsive to signals from the feedback circuit, for providing a control signal to the voltage-controlled phase shifter for degenerating low frequency noise within the oscillator. With such an arrangement, high Q low noise resonators can be switched in and out of the circuit thus providing improved phase noise performance at high power levels with the desirable frequency agility required for a microwave oscillator.

Abstract: An oscillator providing predictable oscillator modulation sensitivity includes an amplifier and a feedback circuit disposed about the amplifier. The feedback circuit includes a resonator having a first port and a second port and a voltage-controlled phase shifter having an input port, an output port and a control port, the input port of the voltage-controlled phase shifter connected to the output port of the amplifier and the output port of the voltage-controlled phase shifter coupled to a port of the resonator. The oscillator further includes a circuit, responsive to signals from the output of the voltage-controlled phase shifter and the first port of the resonator, to provide a control signal to the control port of the voltage-controlled phase shifter for degenerating low frequency FM noise arising within the amplifier.

Abstract: A tunable bandpass filter for radio frequency energy with a phase-locked loop for tracking an input signal and to control the filter to keep the center frequency of the passband coincident with the frequency of the input signal is shown. Using a Yttrium Iron Garnet (YIG) filter as a frequency determining element and as a passive dispersive reference element for a frequency discriminator, the bandpass filter uses the output signal of the discriminator to form a fine tuning signal to control the center frequency of the passband of the YIG filter.

Abstract: A multiple feedback loop frequency synthesizer, having a first and a second feedback loop, each fed by one of a pair of reference frequency signals having a frequency separation equal to the desired frequency separation of the output signals provided by the synthesizer. The frequency of each of such reference frequency signals is greater than the desired frequency separation of the output signals provided by the synthesizer. With such arrangement, because the bandwidth of each of the feedback loops must be less than the frequency of the reference frequency signal fed to such loop, achievement of frequency separation less than the frequency of either one of the reference frequencies enables each of the feedback loops to have increased bandwidth and hence reduced frequency switching times and increased noise suppression.

Abstract: A magnetically tuned resonant circuit having improved noise performance includes a ferrimagnetic or gyromagnetic body such as a YIG sphere which is disposed within r.f. structure, The r.f. structure is disposed between a pair of pole pieces of a biasing magnet and flux return path. Several techniques are described for reducing fluctuations in magnetic fields through the gyromagnetic body. The gyromagnetic body is isolated from conductive surfaces, or the bulk of conductive surfaces in the region adjacent to the magnetic body are reduced. Further, a technique is also described which provides a break in the electrical continuity around the r.f. structure. Each of these technique reduce the magnitude of thermally induced eddy current flow in conductive regions adjacent to the resonant body. It is believed that such eddy current flow produce random magnetic field variations which produce random variations in the frequency characteristics of conventional magnetically tuned resonant circuits.

Abstract: An improvement in a microwave oscillator using a GaAs FET as the active element is shown to include a phase detector responsive to a portion of the positive feedback signals applied to a resonator having a high Q and to a portion of the signals out of the GaAs FET, shifted by 90.degree., to obtain signals to degenerate noise internally formed in the GaAs FET.

Abstract: A frequency discriminator having a wide capture band is shown to comprise, in addition to a conventional phase detector having two channels fed by a signal whose frequency is to be determined (the first one of the channels containing a tuned circuit operative to shift the phase of the signal in accordance with the difference between the frequency of the signal and the center frequency of the tuned circuit and the second one of the channels containing a phase shifter operative to shift the phase of the signal by 90.degree. regardless of the frequency of the signal), a compensating circuit operative substantially to equalize the amplitudes of the signals applied to the phase detector, the compensating circuit including an amplifier in the first one of the channels to amplify the signal out of the tuned circuit, the gain of the amplifier being controlled by a signal indicative of the difference between the amplitudes of the signals fed to the phase detector.

Abstract: A radio frequency phase shifter suitable for X-band operation is disclosed. Such phase shifter incudes a waveguide structure and a ferrite assembly disposed within such waveguide structure. The ferrite assembly has a conductive material plated on the sides thereof. A pair of such plated sides is in contact with the wide walls of the waveguide structure thereby preventing the generation of longitudinal section modes (i.e. LSE.sub.1,1, LSM.sub.1,1, and LSE.sub.1,2) and another pair of such plated walls is displaced from the narrow walls of such waveguide structure to form a pair of waveguide sections cut off to the dominant mode of the radio frequency energy passing through the ferrite phase shifter thereby inhibiting such energy from coupling to wires passing through such waveguide sections for supplying drive current to the enclosed ferrite assembly.