Abstract: A system and method for sensing phase errors in a multiple receiver array use three non-collinear transmitters transmitting first, second, and third signals to a target and receiving corresponding signals reflected from the target using the multiple receiver array. In one embodiment, each transmitter transmits a characteristic signal which can be distinguished from each other by the receivers. In one embodiment, each transmitter transmits a slightly different monotone frequency that is preferably outside any imaging bandwidth. The sheared products computed from heterodyne measurements at the receivers in the array based on the reflected signals from the three transmitters are used to determine and correct for the combined transmitter/receiver phase errors at each of the receivers in the array.

Abstract: The present invention relates to a method and a system for compensating for doppler shift in a signal transmitted between a mobile station and a base station in a mobile communication system. In the method the doppler characteristic is determined for two selected portions of the received signal, the doppler characteristic being in the form of a phased offset for each selected portion. The larger phase offset is them used as a doppler characteristic to provide a doppler shift compensation for the received signal.

Abstract: Radar method and apparatus for detecting small, slow moving targets in the presence of high background clutter that includes a balanced bridge structure to achieve a null balance with the target and background clutter. Radar return signals from background objects as well as the targets are viewed by the radar as a composite single signature return. The invention uses a phase shifter to achieve a null balance even though the background clutter is consists of many components at varying distances from the radar.

Abstract: A method for operating a radar system includes the steps of overlapping mainlobe clutter interference and feedthrough interference in a Doppler output signal of a coherent pulse Doppler radar including the step of phase modulating each pulse of a transmit signal wherein the selected phase modulation is derived from a linear phase ramp required to shift the mainlobe clutter interference into alignment with the feedthrough interference while being held constant over the duration of a pulse. With such an arrangement, the constant phase shift across each pulse has no effect on the performance of intrapulse compression modulation and results in pulse to pulse phase shifts easily being accomplished with existing phase shifters.

Abstract: A system and method for sensing phase errors in a multiple receiver array use three non-collinear transmitters transmitting first, second, and third signals to a target and receiving corresponding signals reflected from the target using the multiple receiver array. In one embodiment, each transmitter transmits a characteristic signal which can be distinguished from each other by the receivers. In one embodiment, each transmitter transmits a slightly different monotone frequency that is preferably outside any imaging bandwidth. The sheared products computed from heterodyne measurements at the receivers in the array based on the reflected signals from the three transmitters are used to determine and correct for the combined transmitter/receiver phase errors at each of the receivers in the array.

Abstract: The present invention relates to a method and an arrangement suitable for embedded signal processing, comprising a number of computational units (100), each computational unit comprising a number of processing elements (20) capable of working independently and transmitting data simultaneously. Said computational units are arranged in cluster, work independently, and transmit data simultaneously, and that said processing elements (20) are globally and regularly inter-connected optically in a hypercube topology and transformed into a planar waveguide.

Abstract: A curve radius of a roadway is determined by measuring the difference in wheel speed of at least two vehicle wheels and the rate of yaw of the vehicle, and hence the curve radius, is determined therefrom. The wheel speeds are determined by measuring the time required for the wheel to rotate by a fixed rotational angle, based on a fixed number of pulses produced by a pulse transmitter which is part of an ABS or ASR system for the vehicle. The method provides considerably improved accuracy using simple, vehicle-contained components and various parameters can be taken into account simultaneously.

Abstract: In a radar system it is necessary to distinguish signals reflected from wanted targets such as aircraft from those reflected from fixed terrain features, known as clutter. The clutter signals can in some cases be significantly stronger than the wanted signals. One method for dealing with land clutter is the use of a high resolution clutter map. The area around the radar is considered to be divided into cells, and an array of background signal estimates is maintained for these cells. Whenever a signal is received by the radar, it is compared with the stored background level for the cell it occupies, and a detection is only reported if the signal exceeds the background by a pre-set threshold. Received signals are also used to modify the stored background levels so that the clutter map adapts to the reflections from clutter which are present over long periods. Clutter maps have so far only been used successfully for radars at fixed locations.

Abstract: A means for identifying a particular range and Doppler shift signal in the field of view of a moving radar antenna which determines azimuth angle to this range-Doppler signal relative to the antenna by determining the phase difference between said signal as processed through two channels each fed by antennas displaced in a horizontal direction with respect to the axis of the antenna system.

Abstract: The present invention provides an apparatus and method for correcting buoy motion in Doppler moment estimates. In the present invention, it is assumed that the buoy is stationary over short periods of time, 0.5 seconds for example. The average pitch and roll angles are measured for the 0.5 second period. A short-term Doppler spectrum for a particular beam is computed and stored along with the corresponding average pointing angle. This short-term Doppler spectrum must be averaged with many others to be able to detect the clear air signal. To correct for motion broadening, the present invention shifts each short Doppler spectrum some number of velocity bins before averaging them together. This shifting scales the measured radial velocity at some measured pointing angle to the radial velocity that would have been measured if the antenna was pointing at some initial pointing angle, typically the steering angle if the antenna was level.

Abstract: An interferometric moving target radar imaging system includes a plurality of simultaneously operating apertures, receivers and processing channels which together coherently process RF return signals to image a moving vehicle. The system corrects for the different phase centers of the apertures and interferometrically combines the return signals from different apertures to attenuate the energy from stationary objects. The true azimuth location of the moving vehicle within main beam clutter spread is then determined which facilitates distinguishing between slow moving and stationary objects to detect the moving objects which are then tracked and imaged in the range doppler domain.

Abstract: Radar detection of accelerating airborne targets in accordance with the present invention utilizing a sequence of velocity, acceleration matched filters. This system includes a transmitter generating a signal oscillating at a predetermined frequency controlled by modulator such that the transmitter repeatedly outputs short duration pulses. The output pulse frequency is passed to an antenna that radiates the energy into free space. Reflected electromagnetic wave energy is received by the antenna to produce a radar return signal that is processed to a receiver that includes a radio frequency amplifier having an output that is mixed with a local oscillator signal an applied to an IF amplifier. An output of the IF amplifier is mixed with the output of an IF oscillator where the mixed signal passes through a low pass filter to a pulse compression network. An output of the pulse compression network is input to a matched filter processor array having multiple outputs applied to an adaptive threshold detector.

Abstract: A radar tracking system 100 adapted for use with existing radar tracking systems. The inventive system includes a radar target detection system 106, 108 for detecting radar targets in clutter using magnitude and angular position information obtained from return signals. A tracking algorithm 104 is used to track and update the positions of said targets with respect to the position of the radar system. The tracking algorithm includes a true target angle estimator 110 for maintaining accurate target angle information when the target is clutter and when the target is out of clutter. The tracking algorithm maintains accurate target distance information when the target is in clutter and when the target is out of clutter. In a specific embodiment, accurate distance information is maintained in a track file 122 where the amplitudes of return signals are stored once a target is detected by the detection system 100.

Abstract: One meter and one foot resolution is achieved in a multi-mode SAR radar system in real time by wide bandwidth RF signal generation, precision motion compensation, polar reformatting, autofocusing and high dynamic range image processing. An exciter/receiver of this system includes means for providing wideband RF waveform generation and down-conversion, while a programmable digital signal processor includes improvements in software for implementing the functions of motion compensation including the presuming of data, polar reformatting, autofocusing and image processing.

Abstract: An ADPCA subsystem includes a weight processor for weighting the delta channel signal according to the results of an adaptive algorithm to which the output of a DPCA vector combiner is input. An AMTI vector combiner is connected to the output of the DPCA vector combiner to form the filter output. The delta channel signal is time delayed and samples of the delta channel signal are collected by the processor together with a sum channel sample and a residue sample, in order to apply the proper weights to the undelayed and delayed delta channel samples. The output of the ADPCA weight processor therefore provides an optimum correction signal to the vector combiner.

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: A method, and corresponding apparatus, for deriving clutter-reduced images of the ocean surface in synthetic aperture radar (SAR) systems. An estimate of ocean surface parameters is first made and subsequently updated iteratively, to provide a reliable model of a selected patch of the ocean as it existed when a series of conventional spotlight mode SAR images were obtained. Based on the estimated ocean model, and on models of ocean wave behavior, of radar scattering behavior, and of the SAR acquisition system, predicted SAR images can be generated, and compared with the measured SAR images, and clutter-reduced images can be produced as a result. In addition to the clutter-reduced images, the method and apparatus of the invention produce an accurate estimate of ocean surface data, and can be used in a reliable approach for detecting hard targets on the ocean.

Abstract: A method for estimating target parameters of a target with respect to a platform such as ownship includes assigning predetermined initial values for the target parameters, wherein the target parameters are part of models having respective model probabilities. The models may include a Kalman filter. The models are updated in response to measured parameters of the target, wherein the measured parameters are different from the ones to be estimated. After a predetermined number of updates, the model having the highest updated model probability may be selected as the winning model. The updated values of the target parameters in the winning model at the time of winner selection are used as the estimated values for the parameters sought to be estimated. The updated parameter values may be refined by restarting the process using the updated values of the winning model as the basis for assigning new initial values for the target parameters.

Abstract: A large bandwidth communication system has a transmitter to transmit signals over a selectable frequency operating range and a receiver having a first mixer for mixing an LO1 signal with received transmit signals. The receiver has a first IF for processing signals received from the first mixer. A frequency synthesizer generates frequency signals for application to at least a transmit mixer in the transmitter and to at least the first mixer in the receiver.

Abstract: The present invention relates to a method and apparatus for producing compensated baseband signal components for a moving radar antenna. A fixed frequency oscillator is used and a baseband signal is complex multiplied by a time dependent multiplicand to produce a signal free of overlap convolution so that clutter signal components are centered around the Doppler frequency f.sub.D =0. Consequently, target detection is as easy as for a stationary radar antenna.

Abstract: A target tracking system (10) comprises sensors (12) which provide data corresponding to a region of interest, the data being time dependent and consisting of amplitudes, ranges and angles. A window (202) is placed around data of interest, the size of the window being determined based on target size, assumed speed and acceleration characteristic, and the window is thereafter broken down into a plurality of smaller windows (208), thereby forming a grid having a nodal point (210) at each corner of the smaller windows. The data within the window is stored in a matrix, and background noise is thereafter minimized by filtering the data past a threshold value (215). The filtered data is analyzed to determine its distance weighted contribution at each nodal point (219), and the weighted distances are summed for each nodal point resulting in a nodal point magnitude for each of the nodal points (220).

Abstract: For motion compensation of SAR images by means of an attitude and heading reference systema mean track angle (.psi..sub.T) flight is selected as desired flight direction;an acceleration (a.sub.x "(t)) is turned through a drift angle (.psi..sub.D) in the direction of a desired flight path;the speed (v.sub.xo '(t)) in the desired flight direction is calculated from a ground speed (v.sub.G (t));a variation of the relative speed (v.sub.x '(t)) in the desired flight direction is calculated by an integration of the acceleration (a.sub.x (t));a relative change of the across heading horizontal position (P.sub.y (t)) is calculated by a double integration of the across heading horizontal acceleration (a.sub.y '(t)), and an actual slant range of the aircraft to an illuminated terrain strip (R.sub.i '(t)) is calculated for each range gate in a manner known per se.

Abstract: A synthetic aperture radar system is mounted in a moving platform. The synthetic aperture radar system includes a multi-beam antenna having a plurality of reception beams different in direction from one another, the multi-beam antenna being adapted to receive radar echoes from objects. The width of each of the reception beams is selected such that the band width of a Doppler shift contained in the radar echo of a moving object is broader than that of a Doppler shift contained in the radar echo of a stationary object. The radar echo is pulse compressed to improve the range resolution before the frequency thereof is shifted such that the center frequency of the Doppler shift due to the velocity of the moving platform becomes zero. After the frequency shifting, the radar echo is filtered to separate the radar echoes of the moving and stationary objects from each other.

Abstract: A device for processing radar signals has the capability of obtaining single or multiple target information as well as target length by utilizing relative radar-target movement. The device includes a radar receiver; an Inverse Synthetic Aperture Radar processor; a list sensor for supplying listing data to the Inverse Synthetic Aperture Radar (ISAR); an element for determining the presence of one or more targets as well as target length; a radar tracking loop for estimating parameters of target motion; and a display unit for displaying the processed information.

Abstract: A method of operating a pulse Doppler radar to increase the probability of detection of an airborne target is shown to consist of transmitting interrogating pulses with a high pulse repetition frequency and processing received signals using any conventional pulse Doppler technique for echo signals having a Doppler shift frequency outside the spectrum of Doppler shift frequencies of clutter and using a DPCA technique at a submultiple of the pulse repetition frequency for echo signals having a Doppler shift frequency within the spectrum of Doppler shift frequencies of clutter.

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 system and technique are disclosed for use in detecting and tracking moving or stationary targets within the antenna field of view. Precise correction of doppler induced location errors is provided by the use of raw sensor data. Return signals are doppler processed, phase shifted and compared in a manner which preserves the angle of arrival of a moving target irrespective of the boresight direction. Stationary target return signals are constructively combined so as to augment the target signal gain independent of the antenna boresight direction.