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.
To provide a variable gain power amplifier with wide dynamic range of transmission power, wherein power efficiency is high, distortion in the linearity is low. In an amplifier with a plurality of transistors connected with cascade, the source of transistor (103) is grounded, the gate of transistor (108) of an output stage is grounded. Further, source bias terminal (109) and drain bias terminal (110) is provided for applying prescribed voltages to the source and drain of transistor (108) of the output stage, respectively. The electric power inputted into transistor (108) of the output stage is passed through without being amplified by applying the prescribed voltages to source bias terminal (109) and drain bias terminal (110), respectively, when the electric power outputted from the output stage is made smaller than a prescribed threshold.
An injection-locked ultra-high frequency solid-state oscillator employs an injection locking method in which an ultra-high frequency output power from a solid-state oscillator is stabilized by injecting an output signal from another stable oscillator. The signal injected into the solid-state oscillator has an optional frequency low enough as compared to that of the output power from the solid-state oscillator and is supplied through a bias supplying circuit or the like. Injection of such low-frequency signal produces sideband waves around the oscillation-wave from the solid-state oscillator while one of such sideband waves is trapped by a high-Q cavity resonator provided in the vicinity of a solid-state oscillating element of the solid state oscillator. The oscillation wave from the solid-state oscillator becomes low noise with the sideband wave trapped, and the frequency of the oscillation wave from the solid-state oscillator is made variable in obedience to the variation of the injection signal frequency.
A four-terminal network in tandem with a tunnel diode (TD) threshold receiver currently used in radar or communications improves its sensitivity. Previous inventors have shown that the temperature and sensitivity properties of a conventional TD threshold device used for detecting very short duration bursts of microwave energy would be enhanced by appropriately biasing the TD by a current derived from the thermal noise; the current sets the TD operating point. The magnitude of the current is determined by a constant false alarm rate (CFAR) feedback loop. The subject invention recognizes that a TD changes states (i.e., a detection event) when the area under the current vs. time curve or the charge passing through the device exceeds a prescribed number of picocoulombs. To maximize the charge and improve detection, a form of superheterodyne conversion is introduced to convert the oscillatory short pulse microwave signal received by an antenna to a monopolar baseband signal. This is done by mixing the incoming signal with a CW carrier whose frequency is precisely chosen so that the resulting beat frequency is one-half of an rf cycle for the given duration of the microwave burst. This maximizes the charge available to trigger the TD. Proper gain and filtering is provided in the adjunct four-terminal network to establish minimum noise figure and appropriate gain to drive the TD held in a CFAR loop. It is shown both mathematically and experimentally that the subject invention can increase the receiver sensitivity by a factor of 20 dB or greater over the prior art. Proper microwave gain is provided to establish the noise figure prior to mixing in the added four-terminal network and a bandpass filter is employed to discard frequency components and the gain of a wideband IF (e.g., 0-500 MGz) is selected to appropriately drive the TD.
A microwave transistor circuit includes a pair of field effect transistors connected in cascade via a standard 50 ohm transmission line having a length equal to one-half the wavelength of the operating frequency range of the circuit. Although the field effect transistors are individually unstable at microwave frequencies, by cascading these transistors the reverse transmission coefficient is sufficiently reduced to render the overall circuit unconditionally stable. In addition, the transmission line is opened to provide physical isolation between the transistors for d.c. bias isolation and a capacitor is connected therein to provide for RF continuity.
