Abstract: A low voltage sensing circuit for a battery powered, micro-processor based circuit is provided. A standard voltage regulator has input voltage from a battery, and output voltage which is fed to a system requiring the same, which includes a micro-processor. A voltage divider is connected through a capacitor to an output port of the micro-processor; and the common point of the voltage divider is connected to the base or emitter of a transistor. Periodically, there is an output pulse from the output port of the micro-processor, which pulse has a predetermined length. During the output pulse from the micro-processor, the transistor may become conductive while the capacitor is recharging. Depending of the configuration, the fact that the transistor is conductive is indicative that the input voltage is either below or above a predetermined value.

Abstract: A mixer is provided having a mixing element, an input signal port for incoming signals at a frequency f.sub.IN, a local oscillator signal port for signals from a local oscillator having a fundamental frequency f.sub.LO, and an output port from which the resultant frequency may be taken. Means are provided to impose a DC component of bias voltage across the mixing element at one of three levels. The mixer is such that it has a pair of conduction threshold voltages which are substantially symmetrical above and below zero volts, beyond which the mixing element will be conductive at least when a signal from the local oscillator is imposed on it. The signal from the local oscillator has substantially sinusoidal voltage waveform, with a peak-to-peak voltage which is greater than the voltage difference between the pair of conduction threshold voltages.

Abstract: A voltage controlled push-push oscillator is provided having a variable frequency output over a range of frequencies. Usually, the range of frequencies is in the microwave range. The configuration is such that the collectors of a pair of transistors are tied together, and an inductive reactance is provided across the base and collector of each of the transistors, with the emitters of the pair of transistors being each connected to opposite phases (at the fundamental frequency) of a resonator which may comprise of one or more elements, bisected to provide an output tap at which an RF null at the fundamental frequency and an anti-null at the second harmonic exists, whereby the second harmonic output frequency of the push-push oscillator is derived. Particularly when the push-push oscillator operates at microwave frequencies, the resonator element is a microstrip line, having the output tap at the centre thereof.

Abstract: Radar detection and signal processing circuits are provided where, following a front end having an RF and local oscillator mixer to an I.F., which is then further mixed against a signal from a swept frequency oscillator, in the presence of a microwave frequency signal, the output of a band pass filter goes to a detector for frequency modulated intermediate frequency signals, and that detector has at least a first output signal that is fed to two pairs of complementary paired comparators, the outputs of which are set to low and high threshold levels. The first pair of complementary comparators has a low threshold level output which is examined by a microprocessor for the incidence of detected low threshold signal in a number of spaced cells--as determined by a clock which divides the detector output into time cells of the sweep period of the swept oscillator. Signal processing is provided so that the incidence of signals in a pair of spaced cells over a given number of consecutive sweeps causes an alarm.

Abstract: A horn antenna construction, particularly for use in microwave radar detector circuits, comprises a molded horn element that is open at its bottom side, with a ridge molded into its flared top surface, and being electrically conductive at least at microwave frequencies such as in the X-band and K-band. The open bottom of the horn element mates to a conductive upper surface on a mounting board, and the horn is drawn down onto the mounting board so that its upper surface forms the bottom of the horn. Thus, the ridge is brought into physical and electrical contact with a feed strip formed in a microstrip board on the mounting board, that has a mixing diode or diodes associated therewith. By this construction, there is a positive and dimensionally stable association of the throat of the horn and the ridge to the feed strip and the mixing diode(s), without the necessity of any solder, inserted connectors or mounting pins, or the provision of any tuning posts or screws.