Abstract: A plurality of threshold detectors is provided to pass analog signals of predetermined and varying threshold values. An analog to digital converter converts these analog signals to binary 1s and 0s. A target detected on each radar beam sweep is a 1 and no target is a 0. These binary numbers are then stored in a reversible up-down counter. At the first signal received, the counter counts up on hits (binary 1) and counts down on misses (binary 0). When the contents of the counter reaches a predetermined count, a target's leading edge is declared. At this time, the counter is then reset and proceeds to count up on misses and down on hits until the aforesaid predetermined count is attained, wherein a trailing edge is then declared.

Abstract: An improved radar receiver having side lobe blanking and coherent side lobe cancellation circuits in the main receiver channel and a control arrangement that overcomes the conventional problem that the side lobe blanking circuit will also blank a noise jammer signal even after the coherent side lobe canceller circuits have acquired the jamming energy. In this system, the side lobe blanking circuits are mechanized with a logarithmic amplifier and with a fast time constant circuit in an auxiliary receiver channel. The fast time constant is selected to match or be slightly longer than the acquisition time constant of the coherent side lobe cancellers. This implementation allows the side lobe blanking circuits to be energized at all times, thus simplifying the operational control of the system. In some arrangements in accordance with the invention the fast time constant may be varied as a function of the amplitude of the jamming signal in the main channel.

Abstract: The elimination of jamming signals from received radar signals is conventionally accomplished by side lobe cancellation techniques. Large interfering signals caused either by clutter or other sources, however, can cause intolerable degradation of coherent side lobe cancellation (CSLC) systems. In the present invention an inhibit signal is used to open the input to the coherent side lobe cancellation error sensing circuits thus preventing large signals from entering the coherent side lobe cancellation loop. Large signals entering coherent side lobe cancellation loops give rise to erroneous transients in the output. The invention effects storage of previously sensed error signals so as to continue jammer cancellation until new data become available to update the error signals. The inhibit signal is generated by a combination of coherent side lobe cancellation sensing circuits and logic control circuits that determine when an inhibit signal should be generated.

Abstract: 1. A system responsive to a composite signal including first signals in the presence of second signals and detecting the presence of said first signals with a selected threshold level ratio of signal voltage to noise voltage comprisingmeans for integrating the composite signal over selected intervals of time,means for comparing a selectable threshold level with the integrated signals,means for storing data to provide said threshold level,counting means responsive to the integrated signals exceeding the threshold level to accumulate a count thereof,constant selector means responsive to the count of said counting means to establish a proportion of the value of said stored data for changing said threshold level to maintain the selected threshold level ratio,and means responsive to said constant selector means for correcting the stored data after a selected number of said intervals of time.

Abstract: A video processor that responds to the video signals received from a group of radar receivers to automatically select the video that is least affected by ECM environment in which the receivers operate. Each receiver in the group has known ECM characteristics so that the effect of different forms of ECM on its video output signals may be detected. By continually monitoring the video output signals different receivers are continually selected to minimize the effect of ECM environment on the radar operation.

Abstract: A constant false alarm rate (CFAR) moving target indication (MTI) radar system, operable in various electronic countermeasures (ECM) environments is disclosed. A modified Dicke-Fix circuit is used to drive the MTI. Operation of the invention results in automatic restoration of signal level out of a filter. Thus the invention provides a CFAR-MTI that is not degraded significantly by swept jammers and is not captured by off-frequency jammers.

Abstract: Due to the long dwell time required for doppler processing, most doppler systems are particularly vulnerable to electronic counter measures environments (jamming). Such vulnerability manifests itself by registering numerous false alarms and by receiver saturation. The proposed system will not deviate significantly from an ideal constant false alarm rate (CFAR) device when operated in an electronic countermeasure (ECM) environment nor will its sensitivity degrade as in conventional systems.

Abstract: A clutter tracker in which received clutter velocity signal is shifted to zero doppler in order that optimum moving target indicator (MTI) cancellaton can be achieved is disclosed. A frequency controllable voltage controlled crystal oscillator (VCXO) is used as the coherent oscillator (COHO) source. The subject digital system changes the VCXO output bus only once per dwell, thus allowing adequate filtering to achieve desired performance without adversely affecting tracking performance.

Abstract: A clutter tracking and cancelling system, for use in a MTI radar system, comprising an auxiliary channel consisting primarily of a phase detector and a canceller. The phase detector provides an output which represents the phase difference between the IF and the coho output, while the output of the canceller, which responds to the phase detector output, represents clutter MTI residue from one transmission to the next. Clutter MTI residue from several successive range bins is smoothed and integrated to provide a control output which is used to shift the phase of the coho frequency, which is supplied to the phase detector in the conventional main MTI channel, to set the mean clutter velocity at zero velocity in order to produce optimum clutter cancellation in the main MTI channel.

Abstract: A radar set for providing accurate low elevation angle tracking of targets by means of controlling the magnitudes of radar detection level which are sequentially switched so that either of a pair of beams is greater in magnitude than is used for two beam tracking.

Abstract: A logarithmetic sidelobe blanking system operable in a pulse compression radar system in which the dynamic range of the blanking system is not limited by the compression dynamic range. A sidelobe blanking receiver is provided to process the sidelobe signals in a manner identical to the processing in the radar receiver. The uncompressed IF pulses in both the sidelobe receiver and the main lobe receiver are sampled prior to their being amplitude limited, and are applied through logarithmetic amplifiers whose dynamic range capability is at least equal to the dynamic range of the preceding circuits. The output signals of the logarithmetic amplifiers are then compared and if the sidelobe signal is larger than the main lobe signal the compressed pulse at the output of the pulse compressor is located and used for blanking to ensure that only the time interval of the compressed pulse width is removed.

Abstract: An improved MTI (Moving Target Indicator) cancelling system that provides cancellation in the first canceller stage of clutter at a first frequency and cancellation in a second or subsequent canceller stage of clutter such as weather or chaff with a substantial doppler frequency offset from that cancelled in the first MTI canceller. The first canceller stage may be a conventional in-phase (I) and in-quadrature (Q) digital MTI unit to develop the I and Q first differences followed by a conversion of these differences into a combined first difference designated as a quantity M and representing an angle times an amplitude multiplier. This M signal is then applied to a second canceller to develop a second difference signal which is then normalized to represent a pure angle term.

Abstract: The elimination of interfering radiation from received radar signals is generally accomplished by side-lobe suppression systems. Large clutter signals, however, can cause a side-lobe suppression system to become almost inoperable. In a high clutter environment the operation of a conventional side-lobe suppression system may also result in a high incidence of false alarms. In the present invention, pulse interference that arrives by way of the main antenna side-lobes that is smaller on the side-lobe suppression channel than the clutter signal appearing on the main radar channel is blanked prior to the implementation of a moving target indication (MTI) channel. A sharply rising interference pulse such as a spike occurring in the auxiliary channel may be detected by a fast time constant (FTC) circuit to provide a sidelobe blanking signal.