A precision current source for providing a stable reference current wherein the current source comprises a reference oscillator and a frequency-to-current conversion network. The frequency-to-current conversion network includes a phase detector, a filter, and a ferrimagnetic resonant oscillator. The phase detector generates an error signal representative of a difference in phase angle between a first signal coupled to a first input terminal and a second signal coupled to a second input terminal. The reference oscillator provides a periodic reference signal to the first input terminal. The filter generates a current reference signal representative of a substantially dc portion of the error signal. The ferrimagnetic resonant oscillator receives the current reference signal from the filter, generates a periodic feedback signal having a frequency representative of the magnitude of the current reference signal, and couples that feedback signal to the second input of the phase detector.

A high power, pulsed microwave frequency converter for a microwave communications system including a phase locked loop with a voltage controlled microwave oscillator that provides at least five watts of pulsed RF output power, the components of the loop being designed to lock on the desired RF output frequency within approximately 20 nanoseconds or during the initial portion of each pulse so that the converter coherently converts two low level signals, one or both of which may be pulsed, into a higher level narrow pulse signal at the sum or difference of the frequencies of the two low level signals.

Phase dispersion between two or more traveling wave tubes (TWTs) is corrected on a pulse to pulse basis by a feedback loop which compares the relative phase of RF signals to be amplified in traveling wave tubes with one another, and provides a phase correction at the input to at least one of the traveling wave tubes such that the phase difference at the output of traveling wave tubes is the same as the phase difference at the inputs thereto, except for any offset therein which may be purposely inserted as desired. The phase difference at the input and at the output is achieved by phase correlators feeding sample and hold circuits, the outputs of which are converted from rectangular coordinates to polar coordinates including an angle; the phase difference angle at the input being compared with the phase difference angle taken from the output.

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.

A frequency synthesizer with at least two main Phase Locked Loops (PLLs) and a signal combiner, where each PLL's input is driven by a reference source of frequency F.sub.refj, and each PLL has programmable dividers in both its input path (M and P) and its feedback path (N and Q). The synthesizer utilizes a method to produce an output frequency F.sub.out that is a close approximation to a requested frequency F.sub.req. The method includes making a series of rational fraction approximations .sup.X i/Y.sub.i to the ratio .sup.F req/F.sub.refj, factoring the resulting Y.sub.i 's into several factors M.sub.i and P.sub.i, picking a pair X.sub.k, Y.sub.k that is a good approximation, but where neither M.sub.k nor P.sub.k is too large for the dividers, and then using diophantine calculation methods and a further equation relating to the way the PLL's signals are combined, to calculate N.sub.k and Q.sub.k. The integers M.sub.k, N.sub.k, P.sub.k, and Q.sub.k are then used to program the four dividers. Several forms of the invention further use a controlled reference source, and by varying F.sub.refj, allow more than one approximation to be made, and the error for each to be determined. After several such calculations, a low error one is chosen, and its M.sub.i, N.sub.i, P.sub.i and Q.sub.i values used. The invention works with synthesizers where the PLL's signals are combined to produce F.sub.out, and with synthesizers where the combined signal is used as a feedback signal for the PLL's.