Abstract: This Doppler radar for the detection and localization of helicopters through blade flashes works in a band located between 300 MHz and 20 GHz and identifies the blade flashes by the width of their frequency spectrum and their duration. It uses, at reception, a multilobe antenna associated with several parallel signal processing chains specialized in the detection of helicopters, enabling detection over a widened zone as well as precise localization. Each chain has a phase amplitude detector PAD (10, 10') followed by a Doppler filter MTI (20, 20') selecting the wide frequency spectrum, a module computing circuit (30, 30'), a contrast circuit (40, 40') eliminating excessively long echoes, a threshold circuit (50, 50') and a false alarm reduction circuit FAR (60, 60') eliminating excessively short echoes. The chains lead to a relative bearing computation circuit (100) performing angle measurements when this is possible.

Abstract: A compressive receiver (10) includes a modulation circuit (14) that modulates the receiver input signal with compensation values equal to the ratio of the transfer function of an ideal linear dispersive delay line to that of the main compressive-receiver linear dispersive delay line (22). An auxiliary linear dispersive delay line (16) dispersively delays the results modulated signal at the reciprocal of the compressive receiver's chirp rate, and the resultant signal is progressively translated in frequency by a frequency translator (18) at the compressive-receiver chirp rate. As a consequence, each point in a signal-frequency component of the input signal is translated to the frequency at which the compensation function was evaluated in modulating the component at that point in time, so the departure of the main dispersive delay line (22) from linearity is compensated for, and increased dynamic range results.

Abstract: This method can be used either as an independent radar system or as an adct to an existing radar system, after suitably modifying the existing system, and will provide a cooperative, Radio Frequency passive, identification system for either stationary or moving targets. The system uses suitable devices that will mechanically vibrate as a transponder mechanism as an attachment to stationary or moving targets. A sideband analyzer is used to identify the viberation pattern in the radar return, and therefore, identifies the target.

Abstract: A pulse doppler radar system for helicopter recognition has a receiver (5) for receiving reflected pulse radar signals. A distinguishing circuit (22) is provided for distinguishing a group of received frequencies within a predetermined spectral range and for ignoring at least the largest amplitude frequency within that group. A threshold detector (24) is arranged to determine when the amplitude of the remaining frequencies in the group exceed a predetermined value to provide a recognition signal.

Abstract: A method for rapidly estimating power spectral density components .rho.(f) in the spectrum of an input signal, by first digitizing the input signal over a selected time interval at a selected sample rate; computing an m-th order prediction error energy as an arithmetic mean of forward and backward prediction error energies; and then computing an m-th order prediction error power from a previous reflection coefficient .GAMMA. computation. A control parameter .alpha. is generated; using .alpha. and .GAMMA., an m-th order entropy H and free energy F are then computed, from which is computed m-th order reflection coefficients as extremes of the m-th order Free energy. If the proper extremes are not found, new feedback for the (m+1)-st order solution is generated. If the proper extremes are found, the spectral components are computed and recorded.

Abstract: A method and device are disclosed for recognizing a target (T) among a plurality of n known targets Ti (with i=1, 2, 3, . . . , n).According to the invention, by direct examination of said target (T) to be recognized and from first values (Cki) representative of a plurality of p recognition criteria Ck (with k=1, 2, 3, . . . , p), at least p third values (pCk(Ti)) are established representative of the probabilities that, for each recognition criterion (Ck), the target (T) to be recognized is each of said known targets (Ti); and said third values associated with the same known target (Ti) are merged while taking into account second values (PCk(Ti)) representative of the probabilities that a target (Ti) is recognized, in so far as criterion Ck is concerned, when it is examined so as to obtain n fourth values (p(Ti)), each of which is representative of the probability that the target to be recognized is one of the known targets (Ti).

Abstract: To provide stationary or mobile radar with the capability of measuring the true range profile, a radar system includes a voltage oscillator coupled to a duplexer via a pulse modulation circuit. A digital control circuit provides a sweeping 500 Mhz frequency (F) of 6N successive batches of pulses being incremented in steps of F/6N. Returns received in response to each transmitted pulse are then combined in a mixing circuit with the signal from the local oscillator to generate a signal IF; each signal is summed with signals for the same range cell derived from earlier pulses transmitted at the same frequency; thereafter the signals pass through a FFT circuit.To maintain the "dissected" spectrum centered at the 2N.sup.

Abstract: A multistage estimator is provided for the parameters of a received carrier signal possibly phase-modulated by unknown data and experiencing very high Doppler, Doppler rate, etc., as may arise, for example, in the case of Global Positioning Systems (GPS) where the signal parameters are directly related to the position, velocity and jerk of the GPS ground-based receiver. In a two-stage embodiment of the more general multistage scheme, the first stage, selected to be a modified least squares algorithm referred to as differential least squares (DLS), operates as a coarse estimator resulting in higher rms estimation errors but with a relatively small probability of the frequency estimation error exceeding one-half of the sampling frequency, provides relatively coarse estimates of the frequency and its derivatives.

Abstract: An apparatus for measuring the frequency of an input signal is described. The apparatus uses a quadrature sampling system to obtain values of the instantaneous phase of the signals at a succession of time intervals, the values being converted into cumulative phase values. An estimate of the frequency is obtained by determining the gradient of the straight line which would best pass through a plot of the values of cumulative phase against time.

Abstract: In order to identify a target a data base is compiled containing records, for each of different known types of object, each record being derived from successive range sweeps of the object as seen from different angles and containing information defining the relative positions of different points of reflection on the object. In order to identify an unidentified object, information from at least one range sweep across it (and preferably a number of such range sweeps taken when viewing the object from different angles) is compared with similar information recorded in the data base to ascertain whether the unidentified object belongs to one of the known types.

Abstract: A method of identifying and detecting remote objects by transmitting wave energy and receiving wave energy reflected from the object. Separate signal parameters pertaining to the wave energy received are processed forming a measured signature of the object. The measured signature is compared with a number of prestored signatures having the same signal parameters relating to known objects of interest. A recording is made of which prestored signatures correspond to the measured signature within predetermined tolerances. Subsequent transmission and reception of wave energy is used for updating the separate parameters and the measured signature. The updated measured signature is compared with the recorded prestored signatures for updated recording of a smaller number of prestored signatures corresponding to the updated measured signature within the predetermined tolerances.

Abstract: A method for compiling and evaluating local traffic data based on a real time evaluation of Doppler echoes on a digital basis, wherein initially the frequency spectrum of the Doppler echo is formed, then the frequency of the maximum amplitude in this spectrum is identified, and the speed of the vehicle is determined from this frequency. The length of the vehicle can also be determined from the speed of the vehicle and from the Doppler echo signal duration. An apparatus for implementing the method includes a millimeter wavelength radar sensor, a transmission unit, and an evaluation unit operating with digital signal processing.

Abstract: Apparatus for recognizing a target such as a ship comprises a radar for successively sweeping the target to obtain input data representing the return amplitude from different target angles; a filter for selecting from the input data those significant ranges at which there is a significantly high amplitude; and a range difference compiler for identifying the frequency of occurrence of each of several range differences between pairs of the significant ranges, the most common range differences (expressed as a histogram) being representative of the distances between major reflectors on the target and thus distinctive of the target.

Abstract: The spectrum analysis arrangement according to the invention covers a filtering and coupling network comprising a setr of narrow pass band filters, with neighboring center frequencies in steps, whose outputs are coupled one to another through delay devices enabling a resultant signal to be obtained which, at each instant, is the sum of the responses of each filter to the same frequency received at different instants by the analysis receiver fitted with a linearly wobulated oscillator. Application to automatic interception stations in order to obtain precise data quickly on the characteristics of transmission spectra to be identified.

Abstract: A microwave frequency detection receiver for receiving an incoming analog radar signal, converting the radar signal into digital form, and performing a table lookup algorithm for detecting frequency and amplitude of the incoming signal with respect to time. The table lookup algorithm is in the form of a three point best-fit sinusoidal approximation of frequency and amplitude for processing successive digital input signal samples processed in groups of three. Digital sampling of the input signal coupled with the novel table lookup algorithm results in detection of frequency and amplitude characteristics on an intrapulse basis.

Abstract: A tracking receiver is disclosed which utilizes optical processing for detecting and tracking input broadband chirp like emission signals. The tracking receiver includes a scanning local oscillator, the output signal of which is caused to be scanned in frequency. A mixer mixes the unknown input signal and the local oscillator output signal to produce an intermediate frequency (IF), frequency difference signal. The IF signal is analyzed in an optical spectrum analyzer which includes an acoustooptical modulator for modulating a beam of radiation, as a laser beam, with the intermediate frequency signal, and optical means, as a lens, for producing a spatial frequency distribution of the intermediate frequency spectrum in a Fourier plane. A photodetector array is provided in the Fourier plane for detecting the spatial spectrum.

Abstract: A pulse doppler radar system for measuring the range to a target. The radar system alternately transmits a signal having a constant frequency and a signal modulated by a linearly-changing-frequency and receives an echo signal from a target. When a plurality of doppler frequencies derived from jet engine modulation are detected in the echo signal, the radar system is operable to obtain the number of frequency differences giving the same range value on the basis of the differences between the detected doppler frequencies, or to selectively use methods of range calculation according to the number of detected doppler frequencies.

Abstract: An improved interferometric spectrum analyser system with direction finding capabilities for an emitting source, the type having a holographic element to provide a laser beam source for the system. The laser beam from the source is focused on a light waveguide within which are arranged in asymetrical configuration with respect to the direction of the laser beam source a plurality of antenna signal transducers and a plurality of reference signal transducer, the antenna signal transducers and the reference signal transducers respectively being arranged in adjacent rows in such a manner as to provide acoustic signals propagating in the same direction within the transducer. A lens assembly is positioned with respect to the light waveguide so as to provide a one-dimensional Fourier transform signal on the X-axis of the waveguide by causing the mixing of the Fourier transform signal of the antenna signal and the Fourier transform signal of the reference signal.

Abstract: Prior art radar systems do not adapt the transmitted signal to avoid the interference bands but only filter the unadaptive receiver signal to eliminate the interference with resulting loss in detectability and distortion that in turn causes loss in resolution and increased ambiguity. The present invention allows a radar system to operate in an electromagnetic environment where co-channel narrow band interference is present, without loss of detectability, resolution and ambiguity. The present invention system adapts the radar transmitted signal so that its spectral energy is significant only in the interference free portions of the radar channel. It next adapts the receiver to detect this transmitted spectrum and then equalizes the signal by means of transversal equalizer coefficients to reduce distortions to the signal sidelobes.

Abstract: Certain man-made structures located in a complex background, such as railroad ties, telephone poles, and fences are detected by a flying craft, using a low powered structure resonant radar system. The radar system transmits a radar signal which includes wavelengths of the same order of magnitude as twice the spacing of the elements of the man-made structure or grating multiples thereof, and transmits them in a plurality of different directions and frequencies. Reflections of the transmitted radar are received and structural resonance backscatter is detected wherein the backscatter amplitude at the resonant frequency is much higher than that at adjacent frequencies or that of the clutter background, indicating the presence of the search-for type of structure. The bright structural resonance backscatter can then be exploted by the structure resonant radar for guidance, homing, etc.

Abstract: An improved radar is disclosed wherein an array of digital numbers describing a target area is produced. The numbers have values representing differences in ranges between the radar and reflecting points in an area on the ground illuminated by the radar. The values also represent the differences in angles between the radar and the reflecting points.

Abstract: A radar apparatus transmits right circular polarized signals and selects the right circular polarized components of the corresponding returns. It also transmits left circular polarized signals and selects the left circular polarized components of the corresponding returns. The selected left and right circular polarized compoments are processed by, for example, averaging them, producing a weighted average of them, or selecting the component of larger value.

Abstract: A method and device are provided for the automatic recognition of targets from "Doppler" echoes. The method consists in comparing sequentially the spectra of the "Doppler" signal retransmitted by each target with successions of spectra corresponding to known targets stored in a dictionary memory and indicating the type of target when the spectra of the signal retransmitted by the target have been recognized.

Abstract: A signal processor for radar systems having phased array antenna structures. The processor determines the angle of arrival of the signal from a discrete energy source. The separate elements or output ports of the antenna structure are sampled to form a matrix of signal values. These values are converted into polynomial expressions consistent with one of the spectral estimating methods of maximum entropy, maximum likelihood, and thermal noise. The roots of the polynomial expressions are found and compared to the distance of the unit circle in a pole-zero diagram. Roots sufficiently close to the unit circle are selected as representative of the source signal peaks and the angular directions to such sources are determined by the corresponding angular location of the selected roots in the pole-zero diagram.

Abstract: An apparatus and method for detecting the polarization signature of radar signals reflected from a target immersed in clutter. The signal to be transmitted is split into individual horizontal, vertical, and 45.degree. polarized signals that are individually frequency shifted, and transmitted simultaneously. The reflected signals are processed in individual horizontal, vertical and 45.degree. channels so as to derive Stokes vectors corresponding to each polarization and describing the scattered field associated with that polarization. The signals representing the Stokes vectors are applied to a matrix computer which provides signals representative of a Mueller matrix which describes how the transmitted signal was transformed by the target and thus constitutes the polarization signature of that target.

Abstract: A sweep frequency, continuous wave (CW) radar tank gauge (3) providing measurement of the level of tank contents or ullage (19), having greatly improved accuracy through improved methods of processing calibrate and return signals directed toward the surface of tank contents (20). Use of sweep synchronous measurement (46) of time domain calibrate/return difference signals (42) and time domain of a virtual "carrier" fundamental in the frequency domain, provide highly accurate measure of tank signal return times. The entire range of return signals is made available for processing and analysis (5), including distinguishable tank bottom reflections.

Abstract: A method and apparatus for use in a pulse-echo imaging or ranging system comprising means (32) for identifying the analytic signal from a received signal and means (34) for extracting ranging information from the analytic signal. The analytic signal can be obtained and processed by digital or by analog circuit means. One embodiment of the analog circuit means (32) includes means (90) for modulating the received signal on a carrier frequency, means (92) for obtaining a single sideband signal from the modulated signal and means (94) for envelope detecting the single sideband signal.

Abstract: A method and system for detecting an object hidden behind and/or under various combinations of optical and/or radar camouflage is disclosed. The radar camouflage is made from material having multiple layers of lossy dielectric and supporting fabric. The optical camouflage is made from material having no special electrical properties but is colored to blend with the supporting scenery. Both types of camouflage material are cut in a random pattern of openings or apertures. The space containing the camouflaged object and other radar-reflective objects is radiated with RF energy at a frequency swept over a predetermined band within the K band of radar frequency bands so that the incident RF waves radiate through the apertures and are re-radiated through the apertures after reflection from the object to create an identifiable scintillation in the reflected RF signal and an enhancement of its average reflectivity at certain frequencies within the predetermined band.

Abstract: When determining the detailed radar reflection cross-section of a radar target by ISAR techniques it is a known problem that one of the target motion components is to be compensated. This was done in the past by complicated numerical calculations of the path of the target. According to the described method, the motion compensation is determined by means of an auxiliary signal which is transmitted form the target. The described method enables the achievement of a radar reflection cross-section by real time data processing of the signals received. Also an apparatus for performing the method is described.

Abstract: A radar transceiver and communications transmitter mounted on a target for communicating video signals from the radar to a remote receiver which has associated therewith an FFT detector for detecting scoring encounters, and a computer or microprocessor which first analyzes the video signals to provide signals indicative of the Doppler frequency shift at a plurality of different times through the use of autoregressive spectral estimation and then computes a model projectile flight pattern, including miss distance and closing velocity, which flight pattern fits the computed Doppler frequency shifts at the plurality of different times.

Abstract: A sweep frequency, continuous wave (CW) radar tank gauge (3) providing measurement of the level of tank contents or ullage (19), having greatly improved accuracy through improved methods of processing calibrate and return signals directed toward the surface of tank contents (20). Use of sweep synchronous measurement (46) of time domain calibrate/return difference signals (42) and determination of a virtual "carrier" fundamental in the frequency domain, provide highly accurate measure of tank signal return times. The entire range of return signals is made available for processing and analysis (5), including distinguishable tank bottom reflections.

Abstract: A process and device for passive detection of helicopters includes detection of helicopter noise and ambient noise by means of an electro-acoustic transducer, and outputting of an amplitude modulated signal therefrom; amplitude demodulation of the signal in the frequency band between 300 Hz and 3500 Hz; spectral analysis of the demodulated signal; and selection and registration of characteristic frequency lines reflective of the rotary units of the helicopter. The process and device permit passive detection of helicopters in the lower noise, higher frequency band, thereby also permitting utilization of smaller antenna arrays.

Abstract: A laser doppler velocimeter with laser backscatter discrimination for determining the relative velocity between an optical platform and another target where a laser beam is generated and directed toward the target. A detector produces a doppler signal in response to the detection of the laser beam. Noise and backscatter signals with bandwidths and amplitudes outside selected thresholds are rejected, and the legitimate doppler signal from the target is enhanced.

Abstract: Target support structure for making bistatic radar cross section measurements. The support structure includes two parallel columns of circular cross section that may be coated with radar absorbing material. The rotational angle of the columns and the spacing therebetween are each adjustable to allow the bistatic reflections from each column to be phased to cancel each other at a selected bistatic angle and thereby minimize the background signal from the support structure.

Abstract: Device for eliminating the noise in 1/f from a Doppler radar comprising in the HF emitting system, a phase coder introducing, at frequency PRF/2 a phase shift of 0 and .pi. alternately, and in the receiving system, after the receiver, a decoder, or gain inverter progrmmable between -1 and +1, acting, in the same manner as the coder, upon the receiving signal and comprising a low-pass filter downstream from the decoder for eliminating the noise in 1/f, that appears at PRF/2, the device being applied to a ground surveying radar.

Abstract: This radar system can be used as an independent entity or as an addition to n operating radar system for acquiring additional data from a radar target's returned signal that is not currently being utilized. The system is to separate the amplitude modulation and frequency modulation sidebands created by the target's surface motion or vibration into independently useable entities. The system measures near carrier AM and FM noises, together with techniques for integrating these elements into a working radar system.

Abstract: This method of constructing microwave systems and processing the signal by correlation is applicable notably to tachometric, telemetric, directional and tracking control systems, to the detection of heterogeneousness and discontinuity in materials by using sensors of the direct-contact or contactless type.

Abstract: The invention of this disclosure comprises a system that simultaneously determines the frequency and direction of arrival of incoming signals. The apparatus of this invention comprises a layered half space dispersive delay line which is utilized as a beam forming element in a device that performs a two-dimensional Fourier transform on a function which is both time and space dependent.A pulse appears at the end of the delay line at a time which corresponds to the frequency of the incoming signal and the position of the pulse along the edge of the delay line is related to the direction of arrival of the incoming signals.

Abstract: A nonlinear technique for high-resolution data processing produces high-rlution power spectra from the output of a conventional processor. First, a "guess" of the spectral estimate is formed. Then the spectral estimate is convolved with the system response function to produce estimated output levels. The differences between the estimated output levels and the measured output levels are used to modify the spectral estimate to produce a new "guess". This process is repeated until certain criteria are satisfied.

Abstract: The receiver comprises a 90.degree. hybrid and analog-to-digital converters etween the RF section and digital processing; which makes it possible to eliminate a phase correlator, four diode detectors and two differential amplifiers used in previous IFM receivers to obtain the sine and cosine signal samples at an initial time and at a delayed time.

Abstract: A method for estimating the high frequency radar cross-section of the sea surface. A Doppler spectrum of the sea surface is obtained by correlating returns from high frequency radar signals. Approach and recede Bragg spectral lines and a zero Doppler frequency continuum level are identified in the Doppler spectrum. The amplitude ratio .rho. between the Bragg spectral lines and an amplitude ratio .zeta..sub.M between the maximum amplitude Bragg spectral line and the zero Doppler frequency continuum are measured from the Doppler spectrum. The radar cross-section is then determined from the ratios .rho. and .zeta..sub.M. In a further method embodiment, the estimated radar cross-section is used to estimate the radar cross-sections of targets appearing in the Doppler spectrum.

Abstract: A system for simultaneously locating a plurality of targets and distinguishing the targets from noise which utilizes phase detector techniques to generate complex voltage signals and obtain phase information. Spectral analysis is performed on the complex voltage temporal functions to generate doppler frequency functions. Both spectral phase functions and spectral amplitude functions are generated from the doppler frequency functions. Spectral phase functions are analyzed using interferometry techniques to determine if a potential target has a common locational source from returns of a plurality of sensors. A zenith angle is also generated using interferometry techniques to provide locational information of the multiple targets. Range gating and two frequency range detection methods provide high resolution range information as to the location of the targets. High resolution range information and two dimensional zenith angle information are used to provide an image of the targets.

Abstract: A coded pulse Doppler radar having apparatus for determining the separation between the frequency spectrum returned from clutter and the frequency spectrum returned from a desired target, and circuitry responsive to the apparatus for adjusting the code to maintain the separation at least at a predetermined minimum value.

Abstract: A frequency modulated continuous wave radar wherein analog signals received from a target are converted to digital form, processed by correlation with differently delayed signals, also in digital form, of a modulation waveform repetitively applied to the transmitted signals and the frequency spectra of the resulting signals are determined, such spectra being indicative of range of the target. In addition, a digital correlator adapted to perform the desired correlation is shown.