Abstract: To reduce emission power, the sounding of a channel comprises a space-of-change transformation of M columns with N initial samples having equal time ranks in the last N impulse responses of a sounding signal received via the channel to produce a transformed matrix, an association with the transformed matrix a matrix of binary elements depending on respective moduli of the samples in the transformed matrix in comparison with a threshold, a spatial filtering of the matrix of binary elements to produce a filtered matrix in which each binary element represents the presence or the absence of the sounding signal in the associated initial sample, and a calculation of an impulse response on the basis only of transformed samples associated with binary elements from the filtered matrix having states representative of the presence of the sounding signal.

Abstract: A method of processing radar returns derived from a new radar waveform. The method processes radar returns derived from transmitting the radar waveform to provide simultaneous matched processing and range profiling of different size objects in the presence of clutter. In the present method, radar returns are digitized and processed to produce pulse compressed radar returns having a predetermined (169:1) pulse compression ratio. A pulse to pulse fast Fourier transform on each RF step is performed on the pulse compressed radar returns. The Fourier transformed radar returns are then simultaneously processed by three processing channels, one each for ships, boats and submarines to provide detection of the different size objects. The waveform permits concurrent detection, discrimination, and high resolution range imaging of detected objects within a single dwell, using a single waveform. Thus, a radar search mode using the waveform integrates several search functions without increasing search frame time.

Abstract: Clutter present in radar return signals as used for wind profiling is substantially removed by carrying out a Daubechies wavelet transformation on a time series of radar return signals. The smoothly varying nature of the return from clutter provides a relatively small number of high amplitude components in the wavelet transformation, which are truncated to remove the clutter. Inverse transformation yields a time series having had a significant amount of clutter removed, without distortion of the radar return from turbulence, which can then be processed to provide useful wind profile data.

Abstract: A police radar utilizing digital data transmission from the antenna unit to a separately housed counting and display unit. The antenna has a double balanced mixer to suppress even order harmonics. The counting and display unit has a computer programmed to perform digital signal processing on the digital data received from the antenna to improve the quality and accuracy of calculated speeds for patrol speed, strongest target speed and fastest target speed. Fastest target speed can be displayed simultaneously with strongest target speed. Signal processing techniques are used to suppress false signals caused by double and triple bounce, harmonics, intermodulation products, video display terminal interference, etc.

Abstract: A system for the instantaneous determination of the frequencies and angles of arrival of a plurality of simultaneously incoming signals. The system includes beam network matrix for receiving the simultaneously incoming signals, the matrix providing one or more superimposed output signal which includes phase information associated with the angles of arrival of the signals. The system uses a Fourier receiver which includes a sampler means for periodically producing a sample of the superimposed output signals and a frequency differentiator for differentiating the sample by frequency into a train of discrete waveforms. Each of the train of discrete waveforms is associated with one of the incoming signals and includes phase information associated with one of the incoming signals. The Fourier receiver further includes a mechanism for determining frequency which determines from one of the train of discrete waveforms the frequency of one of the incoming signals.

Abstract: This method for Doppler spectral processing more readily identifies the profiler radar return signals from the atmosphere in the presence of contamination, e.g., from bird echoes, ground clutter, and radio frequency interference. Profiler radars measure winds in the atmosphere by using backscatter (i) from refractive index fluctuations in clear air due to turbulence or (ii) from precipitation such as rain or snow. These radars also receive contaminating radar returns from ground clutter (e.g., from vehicles, power lines, and trees) and from fliers (e.g., aircraft, insects, and birds). In general, the radar return signals from the atmosphere have statistical and physical properties different from those properties for the contaminating radar returns. This new method uses these differences to eliminate or reduce contamination in radar Doppler spectra for estimation of atmospheric winds.

Abstract: A method and apparatus for hybrid analog-digital pulse compression, as well as, a method of use and manufacture includes an analog intermediate frequency filter, a converter, and a digital correlator. The analog intermediate frequency filter filters and weights returned echo signals, and the digital correlator compresses the filtered and weighted echo signals. The frequency or impulse response of the digital correlator is set based on the frequency or impulse response of the analog intermediate frequency filter to obtain a pulse compressor with minimal mismatch loss and improved sidelobe suppression. The invention provides for the lowest possible sampling rate of analog-to-digital convertors used with the apparatus; thus, minimizing the cost of this device and all subsequent digital processing.

Abstract: A radio communication system for mobile communications, or more specifically, a radio receiver for a base station which receives signals transmitted from a plurality of mobile stations is provided wherein the propagation characteristics of channels with respect to a frequency domain can be instanteously measured at all times even while the channels are in use. A frequency converter collectively receives signals transmitted from the mobile stations and converts the signals to IF-band signals, respectively. The IF-band signals output from the frequency converter are set apart from one another by corresponding ones of frequency differences of the signals transmitted from the mobile stations. Complex Fourier transform deriving means collectively derives the complex Fourier transforms of these IF-band signals, and outputs the resulting frequency spectra to analyzing means.

Abstract: An improved classifier estimates a classification of a sensed object. Data representing the sensed object are received by a sensor, such as a radar, and transformed into wavelet transform coefficients. A subset of the wavelet transform coefficients are selected, the number of coefficients in the subset being fewer in number than the size of the original data. The subset of wavelet transform coefficients is then used in place of the original data by a classifier that generates the classification of the sensed object. The classifier may be a correlation (profile matching) classifier or a quadratic classifier. In another embodiment of the invention, a wavelet fusion classifier further improves classifier performance by taking data from a single sensor, and transforming it into a reduced subset of wavelet transform coefficients for use with a correlation classifier, and also transforming the data into a reduced subset of wavelet transform coefficients for use with a quadratic classifier.

Abstract: The data is processed using a quadratic phase removal process to remove quadratic phase variations contained in the interference to compress the interference to its narrowest extent in a range frequency dimension. Partial motion compensation may be optionally employed using the partial motion compensation process to remove incidental Doppler modulation of the interference caused by motion of the radar during data collection, and to center the Doppler spectrum of radar and interference signals at a convenient frequency. The data is processed using an azimuth Fourier transform to compress the interference to its narrowest extent in an azimuth dimension to localize the interference into peaks while leaving the desired radar signals dispersed throughout the data in one or both dimensions.

Abstract: The present invention improves upon conventional windshear data processing techniques in three mutually exclusive aspects. First, the present invention provides an improved method and system for detecting microburst downdraft candidates. The improvement lies in its capability of detecting multiple candidates in range. Because of the added capability to detect multiple candidates in range, the present invention also provides an improved method and system for azimuthal association of the multiple candidates in range to define an accurate locus of headwind and tailwind pairs. Second, the present invention provides an improvement in that it utilizes a non-circularly symmetric spatial model to compute the vertical component of a total hazard factor. Third, the present invention provides an improvement in the accurate detection of small radii microbursts by correcting bias present in the data from which the small radii microbursts may be detected.

Abstract: A method for measuring the frequency of continuous wave and wide pulse RF signals using multi-purpose, commercial-off-the-shelf test devices, such as an RF signal down converter, a digitizer and a signal processor. The method is based on digitizing the RF signals and dividing the digitized data into blocks of discrete data points. An initial estimated frequency is calculated for the first block of data and used to generate a synthetic signal. The synthetic signal and individual block of data under analysis are summed and tested by a discrimination function through an iteration process to arrive at an estimated frequency for each block of data points. The results are averaged to arrive at the final calculated frequency for the RF signal. The method is suitable for real-time calculations of the RF signal frequency.

Abstract: A Doppler shift compensation apparatus for compensating Doppler frequency shifts in an incoming signal to reproduce a highly accurate signal. The Doppler shift compensation apparatus has high frequency dissolution ability and can detect a frequency, an amplitude and a phase of the incoming signal accurately.

Abstract: A digital signal processing method and apparatus for beam forming utilizes an N-element phased array antenna (1). For transmit side beam forming of an agile beam to be steered in a direction between three adjacent orthogonal beams three copies of complex envelope samples for the required beam signal are generated, separately weighted in amplitude and phase (4) and fed into an N-part inverse FFT processor (3) via three input ports (7a, 7b and 7c) which correspond to the three adjacent orthogonal beams, and inverse Fast Fourier Transformed therein into the required beam as a weighted combination of the three adjacent orthogonal beams for passage to the elements (2) of the phased array antenna (1).

Abstract: The present invention discloses a system for extracting targets from radar signatures. Disclosed is a unique combination of Wavelet technology and neural networks using fractal geometry techniques that estimates the Fractal Dimension of a target even in the presence of high background noise.

Abstract: A solution to the AOA problem is provided, receiving the data via a plurality of antennas, which uses a switching network to couple the antennas to a single receiver and a single analog-to-digital converter to digitize the incoming signal. It is possible to solve the problem where there might be multiple signals present. In the receiver, the incident radiation is mixed with a local oscillator signal and down converted to an intermediate frequency (IF). This IF signal is discretely sampled in the analog-to-digital converter, and further processing is done using digital techniques. The incoming signal has to be phase compared to obtain the angle of arrival. Different delay times are used to receive the digital data from the different antennas at the same sampling times, with the data aligned according to the time axis. The frequency of the incoming signals can then be detected by performing a Fast Fourier Transform (FFT) on the data from one antenna with respect to time.

Abstract: In a method for measuring the distance and the velocity of objects employing electromagnetic waves, the frequency of an emitted signal is modulated. The signals received during one rise and one drop in the frequency of the emitted signal are mixed with the emitted signal. The intermediate-frequency signals resulting from the mixing are then spectrally analyzed. The distance and the velocity of at least one object are calculated from the frequency of the spectral lines of the intermediate-frequency signals during at least one rise and at least one drop in the frequency of the emitted signal.

Abstract: This system compares the phases from Fast Frequency Transform (FFT) outputs to obtain angle of arrival (AOA) information.

Abstract: A process for predictively modelling potential fields in inhomogeneous media is particularly suited for implementation as a Digital Signal Processing chip, as it rapidly predicts the potential field by repeatedly perturbing a trial field solution by a step approximation to the known inhomogeneous media, and then, with one Fast Fourier Transform and one Inverse Fast Fourier Transform, creates a second estimated field solution; a fixed number of such iterations provides a final potential field model, which may be compared with a sensed field to predictively adapt sensor arrays or beam shaping.

Abstract: The present invention relates to a signal processing apparatus for use in radars, which can detect a target from a receive signal by digital processing. An A-D converter samples the receive signal by a clock signal A, and quantizes the sampled value. A clock accelerator generates a clock signal B having a frequency which is N times a frequency of the clock signal A. A signal latch holds an output from the A-D converter for an N clock period of the clock signal B. A digital low-pass filter performs low-pass filtering processing with respect to an output from the signal latch with the clock signal B as an operating clock. As a result, an output from the digital low-pass filter includes a more approximate value of the maximum value in the receive signals. Therefore, it is possible to provide improved accuracy of the target detection by a target detector.

Abstract: A terrain height radar system and processing method comprising a high resolution synthetic aperture radar (SAR) mounted on an air vehicle and a SAR signal processor containing a signal processing algorithm or method for computing terrain height and radar backscatter power. The system contains motion sensing and navigation functions that also provide data to the signal processor to provide motion compensation. Signal processing algorithms in the method compensate for planar motion of the air vehicle for variations of terrain height in the field of view. The algorithms also compensate for nonplanar motion of the radar, and for scatterers in or very near to a reference plane in the field of view. The algorithms exploit defocusing due to displacement from the reference plane to estimate the terrain height above the reference plane. The algorithm is computationally efficient because the bulk of the radar signal processing is common to both the SAR function and the terrain height estimation function.

Abstract: A distant target vibration assessment and signature determining apparatus for operation from a vibrating platform such as an aircraft or helicopter. The disclosed system employs pulse illumination of the distant target and of nearby atmospheric aerosol particles and uses the latter illumination derived signal as a characterization in reverse of the vibrations of the sensor's mounting platform. The nearby and distal nature of the two illuminated energy reflections enables their range gated segregation and individual transformation into the frequency domain. Frequency domain vibration signatures of the distant target and the vibrating platform are then individually obtained and subtracted in order to obtain a clean vibration spectrum representation of the distant target. Variations of the system including a two pulse operating cycle, the use of signal strength evaluation and signal processing alternatives are also disclosed.

Abstract: A radar system transmits dispersed pulses, and receives echoes from targets. The echo signals are digitized and applied over a number of signal paths. In each signal path except one, the digitized signal is multiplied by one of a plurality of differential exponential signals, for converting the echo signal of different exponential signals, for converting the echo signal in each path to baseband, with the baseband frequency representing a particular Doppler which depends upon the exponential signal. In the one remaining signal path, no multiplier is used, and the echo signal is deemed to be at baseband. The signals in each path are applied through a cascade of a pulse compressor and a range sidelobe suppressor. Since Doppler filtering has not yet taken place, full compression and range sidelobe reduction is not achieved, because of extraneous pulse-to-pulse phase shifts.

Abstract: A system for reducing co-channel interference includes a power spectrum analyzer which provides a spectral signal representative of an intermediate frequency signal from the receiver of a direction finding system. The system further includes threshold/window logic that, responsive to the comparison of threshold levels and spectral windows to the interfering signals, will provide stop and continue signals to an integrator. The integrator receives signals from the direction finding system and stops and starts integration of the output signal responsive to the threshold logic. In so doing, co-channel interference is substantially reduced.

Abstract: A signal detection system, preferably for use with a coherent radar system elects certain combination of input signal samples in a block of signal samples to derive a test statistic which is unbiased by Gaussian noise. Products of pairs of sample values are stored in a data sample look-up table. An index look-up table is created by scanning through possible combinations of addresses and excluding those combinations of sample values which would be redundant over other combination and would result in a contribution to biasing by noise. Pairs of addresses from the index look-up table are then used in sequence to access first and second products from the data sample look-up table. The first product is multiplied by the complex conjugate of the second product and the (quadruple product) result is averaged to form a test statistic which is insensitive to position and constant velocity. Detection of the signal is determined by testing the real part of the averaged test statistic against a threshold.

Abstract: Disclosed is a method to extract the periodic properties (or Pulse Repetition Intervals (PRIs)) of radar signals whose time-of-arrival at an airborne platform have been time tagged by an Electronic Warfare (EW) receiver. The PRIs are determined using a modified Discrete Fourier Transform (DFT) written as ##EQU1## where k represents the frequency components, the T.sub.i are the individual Time-Of-Arrival (TOA) data values and N is the last TOA value collected.Disclosed are three possible methods of reducing the number of computations involved with the modification of the Discrete Fourier Transform (DFT) equation to facilitate its use with Radar Time-Of-Arrival (TOA) to extract periodic properties of radar signals. This is particularly applicable to radar pulse trains which are interleaved in time and where each individual pulse train may be staggered or jittered in time so that a time domain deinterleaving scheme must be employed.

Abstract: A conical scan radar system (10) provides return pulses (30) to an A/D converter (38) from which a shaped pulse train is received and stored in a FIFO memory (40). The stored pulse train is then passed through first and second finite impulse response filters (42,44) for achieving sampling rate reduction prior to rendering via a programmable signal processor (64) of target detection identification and tracking.

Abstract: A lower-frequency compact radar system for wide-angle surveillance. Direction-finding receive antennas consisting of colocated orthogonal electric and magnetic dipoles provide target angles from the radar. The size of this antenna unit is reduced to the point where internal noise is comparable to external to achieve maximum compactness. High sensitivity is achieved with an efficient class of pulsed/gated, linearly swept-frequency waveforms that are generated and processed digitally. For backscatter radars, close to 50% duty factors are realized. The rules for waveform design and processing overcome problems of range/Doppler aliasing and/or blind zones. After mixing in the receiver, processing bandwidths are much less than RF signal bandwidths, so that simple, inexpensive personal computers are used for real-time signal processing. Digital FFT algorithms determine target range and Doppler, and DF algorithms determine its angles.

Abstract: Spatially variant apodization is a digital image processing technique for eliminating sidelobes produced by Fourier transform of finite data sequences without compromising mainlobe width. This process allows each sample or pixel in an image to receive its own frequency domain aperture amplitude weighting function from an infinite number of possible weighting functions. In its simplest form the weight is a function of the negative of the current sample divided by the sum of the neighboring samples, and the function is limited to a predetermined range such as the range between zero and one half.

Abstract: Apparatus for the observation and identification of helicopters by means of an FM-CW radar apparatus provided with transmitter means (1), antenna means (2) and receiver means (3). Blade flashes caused by the rotor blades are digitized by A/D converter (4) and processed by Fourier analysis means (5) and processor (6) in order to determine the range from a helicopter to the radar apparatus and the rotor symmetry characteristics. These symmetry characteristics, together with the blade flash repetition frequency yield a substantially unambiguous indication of the helicopter type.

Abstract: An FFT-like array architecture (500), for use on the Doppler filters of a radar system, includes a plurality of stages (505, 506) of weighted butterflies (501, 502, 503, 504), in which each butterfly is provided with four weighting multipliers (410-416). The weights (W1, W2, W3, W4) of the multipliers of the array are determined by an iterative process in which the input and output signals are selected, the input signals are applied to the array, and the actual output signals are compared with the desired output signals to produce error signals. The error signals are backpropagated through the array, to correct the weights. The input signals are again applied, and the corrected output signals are again compared with the desired output signals to produce new error signals, which are again backpropagated to correct the weights. This procedure is used iteratively until the array "learns" the weights which give the desired output signals.

Abstract: A processor for an FM/CW sensor divides the sweep periods of the sensor into a number of subsweep intervals, measures the received power within a multiplicity of frequency windows during each of the subsweep intervals, and then performs a spectrum analysis of the power measurements in each frequency window to characterize the reflectors in the corresponding range bins of the FM/CW sensor footprint.

Abstract: Radar apparatus provided with a transmit generator and antenna means for the transmission of comparatively long, linearly frequency-modulated transmitter pulses. Echo signals are received by antenna means and a heterodyne signal is generated in mixer stage. Propagation time differences for different echo pulses are compensated by means of a dispersive delay element incorporated in the radar receiver. Distortion of the echo pulses in the dispersive delay element is corrected on the basis of a Fresnel ripple correction. A Fourier transformation unit transfers the corrected echo pulses to time domain video with low sidelobes.

Abstract: A microwave apparatus and method for ullage measurement of agitated materials is provided. The apparatus and method utilize a transformation of the reflected time domain signal into a frequency domain signal. The frequency domain signal is averaged using the natural, inherent weighting associated with the transformation to achieve a unique corrected result. The average frequency domain signal is then used to calculate the average distance for determining the ullage measurement.

Abstract: The present invention relates to a pulse Doppler radar wherein the phase position of the reflected signals is evaluated as the most important component in addition to the amplitude. Thus a very good resolution results in the range direction and in the velocity direction for the detection of multiple target situations. The invention can be employed particularly for a so-called HPRF radar.

Abstract: A radar system includes a doppler/pulse compressor/range sidelobe suppressor filter bank (40), which separates received echo signals according to their frequency spectrum into doppler channels, and within each doppler channel performs pulse compression for reducing the duration of the received signals, and also performs range sidelobe suppression, for improving range resolution. It may be advantageous to perform certain types of processing in the time domain, such as determination of spectral moments for estimating velocity spread, mean closing velocity, and reflectivity of a diffuse target such as a weather phenomenon. An inverse (frequency-to-time) transform (50) is performed on the signals produced by the doppler/pulse compressor/range sidelobe suppressor filter bank (40), to produce a reconstructed version of the received signals. In these reconstructed signals, the pulses are compressed, and range sidelobes are reduced. The time-domain processing (62) is performed on the reconstructed signals.

Abstract: A vehicular collision avoidance radar system using digital signal processing techniques including a transmit section that generates a two channel transmit frequency. An antenna both transmits the transmit signal and receives a reflected receive signal. A Schottky diode mixer generates a difference signal having a frequency equal to the transmit frequency minus the receive frequency. A signal switch in a front end electronics section time demultiplexes and samples the channel 1 and channel 2 signals. The samples are coupled to a two-channel analog to digital (A/D) converter. A digital electronics section receives the digital information and performs a Fast Fourier Transform (FFT) on each channel of digital data to determine relative speed and range of a target based upon the frequency and the difference in phase of the two channels.

Abstract: In multiple frequency estimation, the bandwidth and resolution of Fast Fourier Transform (FFT) based frequency estimators are limited by A/D converter sampling rate constraints and also by real-time computational requirements. The disclosed configuration uses a Modified Chinese Remainder Theorem of a paper entitled, "A Noise Insensitive Solution to an Ambiguity Problem in Spectra Estimation" by McCormick et al and a subsampling approach of U.S. Pat. No. 5,099,194 entitled, "Digital Frequency Measurement Receiver With Bandwidth Improvement Through Multiple Sampling of Real Signals" to resolve the frequency ambiguity problem. The configuration extends these ideas to the multiple frequency case. It significantly extends system bandwidth by operating I FFT units in parallel at specific sampling rates chosen to maximize system bandwidth for a fixed level of noise protection.

Abstract: An IFM (Instantaneous Frequency Measurement) receiver is disclosed that can process two simultaneous signals for electronic warfare application. Three IFM receivers are employed (cooperating in the 2 to 4 GHZ range) and have three filters in front of them. Filter 1 is a 2-4 GHz band pass receiver in front of the first receiver. In front of the second receiver is a low pass filter with a band edge at 2 GHz. In front of the third receiver is a high pass filter with the band edge at 4 GHz. In filters 2 and 3, the skirts of the filters are used rather than their pass bands. Details on the signal conditions, calculations for the frequencies, and the equations are disclosed.

Abstract: An interference avoidance system used in conjunction with a vehicular target detection system. The microwave transceiver section of the vehicular target detection system, in which the present invention is incorporated, transmits and receives time-multiplexed microwave signals having at least two channels (frequencies) spaced about 250 kHz apart. The time-multiplexed transmit signal is transmitted and strikes objects (targets) in the environment, and a portion of the transmit signal is reflected back the antenna. A difference signal having a frequency equal to the difference between the frequency of the transmit and the received signal is generated, digitized, and a Fast Fourier Transform (FFT) is performed on the digitized difference signal. A microcontroller analyzes the energy spectrum to determine whether there is interference present. If such interference is present, the microcontroller causes the transmit frequency to change until a frequency is found which is relatively free of the interference.

Abstract: A method of processing electromagnetic signals which are injected into the earth from a capacitor and subsequently detected after reflection from subsurface layers, in order to determine the physical and electrical properties of those layers. The method is based on an iterative process which models the earth as a series of vertically stacked horizontal layers, each characterized by its physical properties of depth beneath the surface and thickness, and its electrical properties of resistivity (or conductivity) and relative dielectric constant. An initial propagation model which specifies the electrical properties of a particular layer or set of layers is constructed and applied to a model input pulse to produce a predicted return pulse which results from the reflection and/or transmission of the input pulse at the boundaries of the layer(s).

Abstract: An AWTSS is shown to be made up of an improved synthetic aperture radar (SAR) for generating radar maps with various degrees of resolution required for navigation of an aircraft and detection of ground targets in the presence of electronic countermeasures and clutter. The SAR consists, in effect, of four frequency-agile radars sharing quadrants of a single array antenna mounted within a radome on a "four axis" gimbal with a sidelobe cancelling subarray mounted at the phase center of each quadrant. Motion sensors are also mounted on the single array antenna to provide signals for compensating for vibration and stored compensating signals are used to compensate for radomeinduced errors. In addition, a signal processor is shown which is selectively operable to generate radar maps of any one of a number of desired degrees of resolution, such processor being adapted to operate in the presence of clutter or jamming signals.

Abstract: In a method for correcting range migration in image generation in synthetic aperture radar (SAR) to eliminate the entire range migration or the residual range migration left by a conventional focussing method, prior to the range compression the data are transformed to the range-Doppler domain and there multiplied by a specific two-dimensional phase function; after an additional range Fourier transformatioin the range compression is then carried out with a specifically modified range transfer function and thereafter a range inverse Fourier transformation performed. Furthermore, a corresponding residual phase error is corrected. In addition, the data can if necessary be segmented in range or a range precompression performed.With the method according to the invention the range migration is completely eliminated without having to perform an explicit interpolation.

Abstract: Radar signal processor for the detection of fast moving targets having small radar cross-sections. A method and apparatus is used to analyze a target that may travel through many range cells during coherent integration time. By transforming the pulse return data into the spatial frequency domain, range bin migration problems have been solved. The signal to noise ratio is also improved thereby permitting the detection of small targets. The processing consists of three major steps: performing an FFT for each pulse to yield spatial frequency components for each return; performing a special DFT for each spatial frequency yielding constant velocity output for each spatial frequency; and finally performing an inverse FFT to obtain target velocity and position.

Abstract: This is a technique for extending the frequency range which employs a power divider having two outputs, one output being supplied to a first A/D converter, and the other output being supplied via a delay device to a second A/D converter. A processor receives the outputs of the two A/D converters. In operation, the input signal is subjected to a known delay .tau. and both original and delayed signals are sampled simultaneously. Both sampled signals are Fourier transformed and the phase and amplitudes calculated, using the expressions:.phi.(f)=tan.sup.-1 [I(f)/R(f)]A(f)=[R.sup.2 (f)+I.sup.2 (f)].sup.1/2where R(f) and I(f) are respectively the real and imaginary parts of the frequency transform. The phase difference between the original and delayed signals is calculated and an approximation to the true frequency for each peak observed in the amplitude spectrum is estimated using the expression.phi.=2.pi.f.tau.where .tau. is the delay.In general, one would expect that when f.tau.

Abstract: A system for distinguishing between a target and clutter analyzes frequency components of returned wave energy by one or more networks each having inputs receiving successive samples of the returned energy and having outputs individually connected to the inputs through multiplier elements providing selectable factors. The multipliers corresponding to each output are connected to the output through a summing element and a selectable and generally sigmoidal activation function. The factors may be bandpass filter coefficients or discrete Fourier transform coefficients so as to generate frequency components of the energy. Predetermined frequency characteristics of the returned energy may be detected by providing the outputs of a network to a network in which the factors are selected as correlation or convolution coefficients, are selected to integrate fed back outputs, or are selected to sum several outputs within a predetermined range.

Abstract: A method for distinguishing between a target and clutter analyzes frequency components of returned wave energy to detect target energy characterized by being present in a narrow range of frequencies, by increasing in the range over time, or by remaining substantially in the range over time. The method utilizes time sequential spectra of the returned energy. The spectra may be signals from a plurality of band pass filters or may be a spectrogram. The energy in adjacent band pass signals and spectra frequencies are correlated to detect energy in a narrow range of frequencies. Differences in successive spectra are integrated to detect increasing energy in a range of frequencies. An energy peak detected in a narrow range by correlation is integrated to detect that the peak remains in the range.

Abstract: A digital pulse compression apparatus comprises a plurality of doppler correction circuits for carrying out doppler correction in the time domain or the frequency domain and for carrying out pulse compression, and a maximum amplitude selecting means for selecting and outputting the maximum amplitude signal out of the compressed signals obtained from the doppler correction circuit at the rate of range bin period. The present invention can supply a pulse compression apparatus having a stable compression performance, even if a doppler frequency of the input signal is not known.

Abstract: A coherent radar is used for achieving high resolution radar imaging of a moving object in sea clutter and noise. A stored replica of the transmitted waveform is combined with the returned signal in a synchronous detector to produce in-phase and quadrature (I and Q or complex) samples. High resolution is achieved by transmitting a series of pulses, each at a different frequency, and then processing these complex samples to produce a synthetic down-range profile. To enhance the radar target or object from system noise and sea clutter, the complex I and Q (in-phase and quadrature component) samples from the radar are coherently averaged in a special two-dimensional slice of the trispectrum (e.g. quadruple product or fourth-order moment). This formulation of the fourth moment retains all important target information and suppresses Gaussian noise. Once averaged, a new set of I and Q samples are reconstructed that produce the same trispectral slice as this average.

Abstract: Apparatus, and a corresponding method, for generating navigational data to aid a pilot in landing or taxiing an aircraft in poor visibility conditions. Radio-frequency (rf) beacons at predetermined locations around an airport runway or taxiway are separately modulated to render them uniquely identifiable from the aircraft. A fixed array of receiving antennas on the aircraft has multiple, angularly spaced antenna beams that substantially overlap each other in coverage, such that a signal received from one of the beacons will in most cases be received in more than one adjacent receive beam. Signals received in each beam are processed by a fast Fourier transform module to separate signal components from the various beacons; then an interpolation process determines the arrival angles of the signals by comparing the amplitudes received in adjacent receive beams.