Abstract: A radar apparatus having a phased array antenna with a large number of transmit and receive modules, a control unit and a video processor. The control unit generates a number of pulse bursts per azimuth-elevation direction, all of which shows slight carrier frequency differences. The video processor determines a doppler spectrum and compared successive spectra for each pulse burst. As a result of the frequency differences, clutter does not show much of a shift while targets which are subject to fold-back in the frequency domain will show considerable shift. A threshold based on a mean spectrum therefore enables detection.

Abstract: According to the present invention, a relatively straightforward, cost-effective technique for eliminating and/or reducing inaccuracies, such as amplitude induced timing errors, is provided in a pulse detection system without reducing bandwidth or degrading the signal-to-noise ratio. Exemplary embodiments detect a change in polarity of slope in a pulse of received energy to provide accurate pulse detection in the presence of noise, without degrading signal-to-noise ratio. Exemplary embodiments can create a time-invariant pulse from a single received, amplitude variant pulse, wherein a rising edge of the detected pulse is coincident with a change in a polarity of slope of the received pulse. Thus, a repetitive pulse signal is not needed to provide accurate pulse detection. Further, exemplary embodiments eliminate any need for complex circuitry since, for example, they are based on using cost-effective differentiators and do not require a reset signal to be asserted between pulses.

Abstract: The device, a microwave pulse signal amplifier, includes an input (E), designed to be connected to a wideband reception head (A, H) suitable for picking up pulse emissions, on which continuous emissions can be superposed, a detection stage (1), connected to this input (E), and providing a rectified signal (SP1), and means for processing (2) the rectified signal (SP1) to establish a rectified pulse signal (SP4), rid of at least part of the effects of possible continuous emissions. The level of the continuous emissions is evaluated by a feedback loop (20, 21) activated (22) when there are no pulse emissions, and is subtracted from the level of the rectified signal (SP1).

Abstract: A laser based range finder which may be inexpensively produced yet provides highly accurate precision range measurements has a number of user selectable target acquisition and enhanced precision measurement modes which may viewed on an in-sight display during aiming and operation of the instrument. Extremely efficient self-calibrating precision timing and automatic noise threshold circuits incorporated in the design provide a compact, low-cost, highly accurate and reliable ranging instrument for a multitude of uses and is adaptable for both recreational and laser based "tape measure" applications.

Abstract: A process and system for improving the detection of signals in additive correlated non-Gaussian noise using multichannel data. This improves detection performance of receivers through the signal processing architecture when the observation data X(n) is first split into an upper and lower path. In the upper path, the known signal is first subtracted from the data and then passed directly to the prediction error filter. The output of the prediction error filters are then input to the zero-mean non-linear processor and their associated estimated variances are used to determine H.sub.0 and H.sub.1 where H.sub.0 denotes the condition where no signal is present in the data and H.sub.1 denotes the signal present case.

Abstract: Receiver dynamic range is improved while maintaining system processing fidelity by placing a processor control attenuator in front of the synchronous detector or other circuitry and A/D converter circuits. This is followed by a digital circuit which reinserts the attenuation that was taken out previously to maintain signal processing fidelity. The control for the attenuator function is from the processor and is determined by looking at the prior pulse repetition intervals (PRIs) of the radar system data and determining from that data what attenuator value to use for the next PRI. This is done for each range bin to be processed.

Abstract: A method and apparatus for controlling the false alarm rate of a receiver which detects each received signal having a power level greater than a predetermined threshold level which is received within a predetermined detection interval. The receiver is adapted to receive signals in response to source signals having a predetermined transmission period. The signals detected within each transmission period can include an initial signal and a plurality of excess signals received subsequent to the initial signal. The total number of detected signals and the number of excess signals received within the predetermined detection interval are counted and a ratio therebetween is determined. Based upon the ratio of the total number of signals to the number of excess signals, the relationship between the power level of the received signals and the threshold level is adjusted in order to control the false alarm rate of the receiver.

Abstract: A time efficient method for processing digitized doppler radar signals and establishing adaptive target detection thresholds which are used to distinguish targets from noise and clutter. After subdividing the range-doppler matrix into several equally-sized parallel processing elements, the radar system's signal processor executes this process on each processing element in parallel. This process involves the processing of the digitized radar signals stored in each parallel processing element by integrating over the amplitudes of each data cell in a given parallel processing element. This, in turn, yields a secondary data array for each parallel processing element equal in dimension to the parallel processing element itself. Target detection thresholds for all cells in each parallel processing element can then be established from the values stored in these secondary data arrays.

Abstract: A monopulse thresholding processor and method for improving resolution by using the difference channel data to eliminate "excess" sum channel returns. The processor may be used with a radar system that comprises an antenna, a transminer, a receiver for processing transmitted radar signals to produce radar returns therefrom, a log compressor for converting radar returns to log values, and a display for displaying the radar returns. The signal processor comprises a left sum and right sum generator coupled to the receiver for computing a left sum and a right sum from radar returns generated by the receiver. A pseudo-difference generator is coupled to the left sum and fight sum generator for generating pseudo-difference channel data. A beam sharpener is coupled to the left sum and right sum generator and to the pseudo-difference generator for beam sharpening the radar returns.

Abstract: Radar apparatus provided with a signal generator (1), transmitter means (2), antenna means (3), receiver means (4), a video processor (6) and an indication device (7) for the generation of a radar picture of the surroundings of the radar apparatus with a first resolution. A selected target, designated with control unit (8), may be displayed on the indication device (7) with a second, higher resolution. To this end signal generator (1) generates in the direction of the selected target control signals for transmitter (2) with an increased bandwidth. Selection and conversion unit (5) matches echoes of these increased bandwidth signals to the bandwidth of video processor (6) and indication device (7).

Abstract: A method of detecting a target signal at a target signal level below the level of clutter in the return signals of a radar receiver. The receiver i.f. signals are correlated by multiplying delayed i.f. signals with undelayed i.f. signals. The correlated signals are filtered and then decomposed into their spectral component frequencies. The spectral components are compared, in turn, with individual thresholds. The individual thresholds are formed by summing the weighted values of selected ones of the spectral components, the selection being such that the spectral component being compared with a threshold is not used in forming that threshold. A target output signal is generated whenever any one of the spectral components exceeds the level of the threshold against which it is compared. In a second embodiment, in-phase and quadrature correlator signals are formed by the use of two correlators and two delay lines having different delay times that provide a 90 degree phase difference.

Abstract: 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.

Abstract: A process for mapping a region of interest using polarimetric radar signals is disclosed. The process provides for the polarimetric calibration of polarized signal data to account for distortions arising from cross-talk and channel imbalance during signal transmission and/or reception. Moreover, the process also can be used to correct for ionospheric signal distortions of polarized signals with low frequencies prone to Faraday rotations upon encountering the ionosphere. Such calibrations are accomplished with a reduced number of, typically ground-based, signal reflection devices used for calibrating the polarimetric signals to compensate for the above distortions.

Abstract: A wideband radar apparatus is provided having improved interference suppression characteristics. The known time versus bandwidth characteristic of the transmitted pulse is utilized to effect intermediate frequency bandwidth reduction in received swath echo signals. During the interpulse period, basebanded swath echo signals are then subjected to a series of adaptive interference suppressing updates. The adaptive weight vector produced during each of these updates is then applied to the same data used to generate the weights. Preferably, adaptive weight generation is performed in a systolic array according to a QR decomposition algorithm.

Abstract: The signal that controls the gain of a sensitivity timing control (STC) circuit is slimmed with a gain correction signal to compensate for gain variations introduced by items such as variations in the parameters of electronic components. A known test signal is injected into the STC circuit and the resulting output signal is measured. The amplitude of the gain correction signal is determined based on the difference between the desired output signal amplitude and the measured output signal amplitude.

Abstract: Disclosed is a method for the adjusting of the detection threshold of a radar receiver for a distance zone called a search zone surrounded by distance zones called adjacent zones, fitted out with a module enabling the computation of the mean value as a function of the distance of the ambient noise along an axis starting from the receiver wherein, for each search distance zone, the detection threshold is raised by a zero value when the ambient noise is low and by a value that increases monotonically with the level of the noise measured when the ambient noise is greater than a pre-determined threshold.

Abstract: An automatic thresholding target detection system operable in high clutter, noisy environments provides target recognition through the generation of automatic signal thresholds. Infrared and radar detectors scanning an environment detect radiant energy from manmade and natural sources. The energy received is converted to electrical signals representative of the varying energy intensities which are filtered and compared with a computed target signal threshold. Signal spikes having amplitudes greater than the automatically generated threshold are then evaluated using a shape parameter test. Finally, an automatic region clutter recognition processor confirms that the spike is a true target, clutter or noise.

Abstract: An adjustable bandwidth signal energy detector apparatus utilizing a detector processor to process serial frequency data to determine which of N frequency bins contain signal energy. The serial frequency data is processed through a series of low pass filters, each of which include a series of point delay. The data from each point delay series is summed and outputted to a detection combiner wherein a sequence of N binary number is generated.

Abstract: A distortion correction circuit having a mechanism for intercepting a distorted output signal from a receiver and for generating an Nth order signal. A circuit is provided to subtract the Nth order signal from the distorted output signal for providing a circuit output signal. Finally, a feedback loop is provided to feed back the circuit output signal for controlling the Nth order signal and for providing a distortion corrected circuit output signal. In a preferred embodiment, the distortion correction circuit includes a calibration circuit which provides a calibration signal employed to linearize a receiver channel. The receiver channel includes a plurality of receiver stages which receive the calibration signal and provide the distorted output signal which is intercepted and directed to a cubing circuit. The cubing circuit generates an error correction signal controlled by the feedback loop to cancel the distortion component of the distorted output signal.

Abstract: An apparatus comprises a signal input and a sampler and analog-to-digital (A/D) converter coupled to the signal input. The sampler and A/D converter forms a digital pre-look signal from an input signal. The apparatus further comprises a digital memory coupled to the sampler and A/D converter. The digital memory stores sensitivity time control (STC) data and provides specific STC data in response to the digital pre-look signal. The apparatus further comprises a digital-to-analog converter coupled to the digital memory. The digital-to-analog converter converts the specific digital STC data to a first analog STC signal. The apparatus also includes a first comparator coupled to the signal input and to the digital-to-analog converter. The first comparator has an input for receiving the first analog STC signal. The first comparator compares a present input signal to the first analog STC signal to provide a detection signal.

Abstract: An adaptive RADAR environmental signal filter (1) is described which selectively preprocesses RF RADAR input data prior to the data's utilization by a processor (8). The filter (1) consists of an array of parallel discriminator cells (165) which compare incoming RF RADAR data to a window parameterized by predetermined threshold values. The array of discriminator outputs are networked through combinational logic (59) in order to provide an output correlation signal (63) to an external processor (8). A discriminator enable latch (55) synchronizes the discriminator outputs as the outputs pass through the combinational logic (59).

Abstract: A pulsed doppler radar system having an improved detection probability, comprising an antenna unit, a transmitter for transmitting a signal through the antenna unit, a receiver for receiving a signal reflected by a target through the antenna unit to provide a reception signal. A processing unit which receives the reception signal from the receiver determines, in accordance with a range of the target and a signal-to-noise ratio and bandwidth of the reception signal, an optimum integration number which maximizes the detection probability and performs coherent integration on the reception signal by the number of times equal to the determined optimum integration number thereby outputting a signal having a predetermined level. Such a signal is fed to a display and an image of the target is displayed on a display.

Abstract: A method of measuring a distance to an object includes generating first signal pulses to be bounced off the object and receiving the first signal pulses, after the first signal pulses have been bounced off the object, as second signal pulses. When the amplitude of the second signal pulses is above a predetermined value, the second signal pulses are differentiated and then supplied as differentiated second signal pulses to an input of an analog-to-digital converter. When the amplitude of the second signal pulses is not above the predetermined value, the second signal pulses are passed through to the input of the analog-to-digital converter unchanged. Signal pulses at the input to the analog-to-digital converter are converted into digital signals. The digital signals are summed over a period of time to generate a sum. The sum is used to determine the time delay between generating the first signal pulses and receiving the second signal pulses. The time delay is proportional to the distance to the object.

Abstract: The maximum amplitude of an input signal (IN) is compressed or reduced to a smaller value suitable for operation on the compressed signal (OUT) by a downstream signal processing stage (16) having insufficient dynamic range, ratio of maximum amplitude to root-mean-square (RMS) noise, to accommodate the original input signal (IN). The input signal (IN) is digitally sampled with coarse resolution to generate a correction signal (44) having a waveform which approximates only the large signal components (24) of the input signal (IN). Where the input signal (IN) consists of recurring received radar pulses, the large signals (24) represent clutter. The amplitude of the correction signal (44) is lower than and increases as a predetermined function of the amplitude of the input signal (IN), and is subtracted from the input signal (IN) so that the large signal components (24) are reduced whereas the small signal components (26), which represent desired target information, retain their original amplitude.

Abstract: A gain control network having a phase splitter circuit responsive to an RF input signal for providing first and second RF signals that are out of phase relative to each other, a first series of switched gain control elements, and a second series of switched gain control elements substantially identical to the first series and commonly controlled therewith. The first series of gain control elements is responsive to the first RF signal for providing a first gain controlled signal, and the second series of switched gain control elements is responsive to the second RF signal for providing a second gain controlled signal. A phase combining circuit combines the first and second gain controlled signals to provide a gain controlled RF output. By performing gain control with two gain control channels having substantially identical circuits and common switching control, transient glitches in each of the channels are substantially identical and are substantially cancelled via the phase combiner.

Abstract: A method and apparatus of point target filtering in a weather radar system for eliminating point targets such as airplanes in real time. A one-dimensional filter is used that operates on a single radar dwell of data at a time. The filter searches for point targets in a reflectivity data field by looking for increases and decreases in the magnitude of the radar return. Each sample volume of the radar dwell is compared to adjacent sample volumes and the differences are tested against predetermined point target thresholds. The differences greater than such predetermined thresholds are flagged. After the entire radar dwell is processed, flagged point target data in the sample volumes are replaced with the data from the sample volume just before the point target which is not considered to part of the point target. The point target filter removes the point targets and the performance limiting contamination they represent to automatic weather data processing programs.

Abstract: An adaptive pulse signal threshold detector is disclosed wherein detected signals are analyzed to determine the strength of the signals and the system is adapted for increased or decreased sensitivity on the basis of the detected signal strength. The adaptive pulse signal threshold detector subjects the detected signals to three threshold criteria during a signal validity analysis. The adaptive pulse signal threshold detector causes the system to be adaptive in so far as the system responds to detected signal strength to alter the detection criteria. The adaptive pulse signal threshold detector includes a binary detector.

Abstract: The invention relates to a radar apparatus provided with a detection unit, which determines the positions (12) of objects incorporating fast moving parts, such as helicopters. The detection unit thereto comprises a first range-azimuth area (3), a trend estimation and standard deviation calculation unit (5), a threshold (8), a second range-azimuth area (9) and a clusterer (11).

Abstract: A pulse radar apparatus is provided with a transmitting unit (4) for the transmission of a modulated transmitter pulse Y.sub.t, a mixer (9), an IF amplifier (11) and a quadrature detector (12) for the reception of signals Y.sub.r and the correlation of signals Y.sub.r with a replica X of the emitted modulated transmitter pulse Y.sub.t, to obtain an in time compressed correlation signal .sigma..sub.xy (.delta.). The pulse radar apparatus is also provided with a pulse discriminator (3) to enable, on the basis of at least one amplitude .vertline.Y.sub.r .vertline. of the received signal Y.sub.r and at least one amplitude .vertline..sigma..sub.xy (.delta.).vertline. of the correlation signal .sigma..sub.xy (.delta.), differentiation between the signals Y.sub.r, possessing modulation, and interference.

Abstract: A constant false alarm rate (CFAR) circuit uses three windows for calculating mean level thresholds. In addition to a lead window and a lag window each separated from a cell of interest by a predetermined number of cells, a straddle window is used which includes the cell of interest. Each of the lead, lag and straddle windows are subjected to editing to remove three adjacent cells including the cell with the highest power level. The remaining cells are used to calculate a mean level threshold for each of the three windows. The largest of the three mean level thresholds is used, unless it is derived from the straddle window and it is significantly larger than the largest of the mean level thresholds derived from the lead and lag windows. In addition, use of the mean level threshold derived from the straddle window may be excluded for range cells associated with one or more range and azimuth.

Abstract: An accumulated statistics CFAR method and device operates using integrated data to maximize the probability of target detection for a given false alarm rate. The CFAR hardware varies its detection criteria as a function of the statistics of the range gate in question. The detection threshold is based on other range gates seen in the past which contain the same terrain type.

Abstract: A target signal detecting apparatus for discriminating and detecting a target signal from a noise signal having an amplitude characteristic which exhibits the Weibull distribution. A received signal whose amplitude intensity distribution is in accordance with the Weibull distribution with its probability density function Pc(x) given by the following ##EQU1## is subjected to logarithmic transformation so that a mean-square value <y.sup.2 > of the amplitude of the logarithmically transformed received signal (y=lnx) and a square value <y>.sup.2 of the mean are calculated and a distributed parameter C is calculated in accordance with the mean-square value <y.sup.2 > and the square value <y>.sup.2 of the mean as follows ##EQU2## Then, the calculated distributed parameter C is compared with a predetermined threshold so that if the distributed parameter C is greater than the threshold value, it is delivered as the distributed parameter corresponding to a target signal.

Abstract: An RF multiplexer divides an incoming signal from an RF antenna into disce frequency bands. Each frequency band has its own separate circuit on separate lines to operate on the frequency band and determine if a radar signal is present or if only noise is present on the line. This is done by comparing the incoming signal for magnitude with a DC signal that is generated within the circuit and is proportional to the noise within the frequency band. An indication that any of the signals within the discrete frequency bands exceed the DC signal generated within the same band results in an alarm indication.

Abstract: A radar equipment comprising a display unit (FIG. 1) and a scanning unit (FIG. 2) linked together by electrical conductors (94,72,106,26) for the transmission of information and/or control signals between the units, and circuitry (90,98; 66,69; 102,108; and 25,162, respectively) for superimposing on an individual conductor more than one of the signals.

Abstract: A pulse marine radar system having a threshold generator providing a range dependent threshold waveform which is a function of sea conditions, rain conditions, and radar parameters. Based on the radar settings and inputs from the operator regarding the sea and rain conditions, a processor uses a mathematical model to compute the mean of sea clutter, rain clutter, and receiver noise for each of a plurality of successive range intervals. In response to the mean values, a generator generates a range dependent piecewise linear analog waveform which is subtracted in range sychronism from the receiver video. Next, the video is filtered. For each range interval, the processor also calculates a threshold based on the probability of sea clutter, rain clutter, and receiver noise exceeding the threshold after subtracting the mean. In response to the threshold values, a generator generates a piecewise analog signal which is compared with the output of the filter to digitize the radar video.

Abstract: A crystal video receiver having CW and pulse detection capability includes a threshold signal generator which switchably provides fixed and noise riding threshold signals, used to determine initial signal detection. Track and hold circuits provide a second threshold, derived from the peak received signal level, for establishing the termination of received video pulses. A pulse width counter is coupled to determine the time a received pulse signal is between the two thresholds and is set to overflow at a predetermined time after the reception of a signal to establish a pulse representative of a received CW signal and to prevent receiver lock up.

Abstract: A circuit for generating an output signal L indicative of the mean clutter level at a selected location in the field of view of a radar apparatus, particularly the sea surface which exhibits a swell pattern. The circuit includes processing circuits which generate weighting coefficients (a.sub.1, a.sub.2, . . . a.sub.N) used to weight the amplitudes of returns derived respectively from a group of N discrete locations which precede in range and or succeed in range the selected location. The circuit generates the elements r(n) of a matrix [r] which represents the auto correlation function of the amplitude of returns derived from w discrete locations encompassing the group of N locations. Circuit then uses the matrix [r] to compute the weighting coefficients (a.sub.1, a.sub.2. . . a.sub.N) which are stored at 13 applied to respective multiplying circuits to weight corresponding amplitudes accessed to respective locations of a shift register.

Abstract: To suppress rain echos in a terrain tracking radar with elevation monopulse devices, the signal in the difference channel is amplified by a predetermined factor. By comparing the level of the sum signal with the amplified difference signal, conclusion is reached about the presence of a ground echo or a rain echo. The factor should preferably be automatically adjustable according to the level in the sum channel.

Abstract: A radar system includes a variable delay circuit coupled between the transmitter and the receiver switch. A feedback loop including a comparator and an integrator is coupled between the receiver envelope detector and a control terminal for the variable delay circuit. The feedback loop controls the amount of delay of the receiver switch to maximize sensitivity to close range targets.

Abstract: The invention relates to a process for adapting the post integration in a switched pulse repetition frequency radar and a circuit implementing this process. For that, the post integration of the detected signals is effected as a function of the signal received from the Doppler filter. For that, switches are used controlled by comparator circuits.The invention is useful in frequency ambiguous coherent Doppler radars using recurrence frequency switching by blocks.

Abstract: An adaptive detection threshold system for moving target detector and moving target indicator radar systems. The threshold system uses data from the echo input signal to reconstruct a threshold level closely resembling the output clutter residue in doppler filters due to point clutter sources. At least three azimuth data values are used, with the values being from adjacent coherent processing intervals and separated in azimuth a distance approximately equal to the beamwidth of the antenna system. The data at the same range from the three azimuths is combined to form an estimate of the residue at the output of a doppler filter, assuming that the echo is caused by point clutter. Compensation for radar instability and changes in scan rate or interpulse period is included. Data from conventional constant false alarm rate processing designed to control alarms from distributed interference, such as weather echoes, is also used to compensate the residue estimate.

Abstract: A radar signal processor which operates without clutter canceller and AGC circuits by applying an adaptive weighting circuit which adjusts the FFT weighting function on a range gate basis to account for clutter in that range gate. An input buffer determines Log.sub.2 values per range gate for use in the weighting operation and a normalization circuit scales the weighted FFT output to facilitate post-processing.

Abstract: The application describes digital signal processing of radar video signals to provide an optimum display. Three interacting components of the system are further described in detail: a global mean estimating circuit, a statistical analyzer circuit, and a dynamic range compression circuit. The global mean estimating circuit determines the mean of the amplitude distribution of video signals over a wide section of the display as opposed to a local mean of signals. A local mean of signals is the mean of the amplitude distribution of video signals occurring in the near vicinity of a point on the display. The statistical analyzer circuit evaluates the amplitude distribution of video signal samples and controls the gain of the signal path so that the variance of the sampled amplitude distribution follows the variance of a model distribution. The dynamic range compression circuit functions to compress the range of amplitude distribution in a manner to provide maximum information from the display.

Abstract: An adaptive radar signal processor is operable to effectively suppress clutters and extract a target signal with a high degree of accuracy and includes a memory storing two-dimensional radar data corresponding to range and azimuthal directions, multipliers multiplying each of data of the same range but different azimuthal direction read out from the memory, an adder generating the added data of the multipliers as an estimated data, and a weighting coefficient determinater which determines the optimum weighting coefficients based upon the stored radar data so that the difference between the radar data and the estimated data at an observing position is minimized, and produces the difference data as a clutter-suppressed radar data.

Abstract: An adaptive radar signal processing apparatus for a radar system wherein filter coefficients are switched for individual regions so that optimum filter characteristics can be obtained for the individual stationary clutter region, moving clutter region, clear region, etc. thereby providing suppression of undesired signals which is adapted for each region.

Abstract: A radar, e.g. as used for the surveillance of aerial navigation, has a receiver feeding incomimg echo signals to several Doppler filters in parallel, the output signal of each filter beign passed to a utilization stage through a respective attenuator connected to the filter output in parallel with an associated area processor. The latter comprises a pulse counter synchronized with the scanning motion of the radar antenna to register the number of echoes received in successive sweeps from different zones into which the surveyed space is divided in distance and azimuth. Upon the last sweep of a sector encompassing a group of such zones, the contents of respective cells of a sector memory loaded by the pulse counter are compared with a first threshold. If the number of echoes stored in such a cell exceeds that threshold, a count written in an assigned cell of a scan memory is incremented; if it does not, the count is decremented.

Abstract: A radar detector is disclosed which comprises a radar wave signal receiver for producing a detection output when the incident radar signal is synchronized with a local oscillation frequency at a certain sweeping time, first and second pulse train signal generators for producing pulses with different cycles, and a cycle alteration circuit for altering the cycle of the second pulse train signal generator in accordance with a logic output corresponding to the detection output from said receiver, thereby synchronizing such cycle with the cycle of the first pulse train signal generator. The regular radar wave signal is discerned by the detection of coincidence between the output pulses from the first and second pulse train signal generators at certain time intervals. Consequently, the radar system is prevented from responding to interference noise or extraneous radar waves.