Abstract: An antenna and system for determining two-dimensional angle-of-arrival includes circular array interferometers for azimuth, linear interferometers for elevation, and a mast for positioning the interferometers in a vertically stacked orientation. The circular array interferometers exhibit azimuth constant-phase-difference contours orthogonal to elevation constant-phase-difference contours exhibited by the linear interferometers. An antenna and system for determining azimuth of input signals includes ambiguous and non-ambiguous circular array interferometers. The non-ambiguous circular array interferometer resolves ambiguities introduced by the ambiguous circular array interferometer, the at least one ambiguous circular array interferometer operatively coupled to a low-order Butler matrix and power divider/combiner such that a high order Butler matrix is not required to generate omnidirectional phase modes from the ambiguous circular array interferometer.

Abstract: A direction-finding method for determining an incident angle of a high-frequency electromagnetic signal in a system including at least two receiving antennas spaced apart by a known distance. the antenna output signals of the at least two receiving antennas are converted, together (in accordance with a multiplexing procedure) or individually, into the frequency domain through a Fourier transformation, followed by a conversion into an IF range and an A/D conversion. In this range, the phase difference between the output signals is determined and the signal frequency of the incident wave is determined through a phase-sequence analysis. The incident angle of the incident wave is determined from the phase difference and the signal frequency.

Abstract: A linear interferometer antenna for making azimuth angle measurements and elevation angle measurements of an identified target. The antenna includes six radiating elements which receive signals sent from the target, a beam forming network, and a processing unit. Four of the six radiating elements are positioned on a first plane and the remaining two radiating elements are positioned on a second plane. The second plane is parallel to and positioned at a predetermined distance from the first plane.

Abstract: A system is disclosed for estimating the position and velocity of a moving transmitter making use of both Doppler frequency measurements and LBI phase measurements. The frequency measurements and the LBI phase measurements are made from a platform moving through said measurement path. The estimation is based on equation models ##EQU1## These equation models are used in cost evaluations in grid searches to provide initial estimates of parameters defining the position and velocity of the transmitter and the initial estimates are used in nonlinear least squares calculations based on the equation models to provide an estimate of the position and velocity of the transmitter.

Abstract: A method for estimating the number of emitters of intermittent or periodic pulsed energy waveforms received at a sensor location and the parameters of the intermittent or periodic energy waveforms, including: accumulating over a selected period of time output of the sensor, the output consisting of a set of vectors, each of the vectors consisting of at least one element of parameters of direction, frequency, and amplitude, and which element(s) specify(ies) a point in a space defined by the element(s) for each of the waveforms received when at least the parameter of direction is included; dividing the space into a plurality of bins, considering each vector in turn, and apportioning weight of each vector to be accumulated within at least some of the plurality of bins; determining at the end of the selected period of time which of the bins exceed a threshold strength and are, therefore, the emitters; and calculating the at least one element of parameters for each emitter as appropriate for the vector elements se

Abstract: An antenna array for radio interferometry uses three equi-spaced triplets set vertically above the ground with different respective spacings, the center antenna of each triplet being at a different height. Signal processing circuits provide for each triplet a signal which is a function of the elevation angle .theta. but is independent of the ground reflection coefficient, P. the signals are weighted to give the optimum value of .theta., e.g., by selecting the signal varying most rapidly with .theta.. Some antennae can be shared and for example three triplets may be provided by seven antenna elements.

Abstract: This invention provides a method and apparatus for determining position from code modulated, suppressed carrier signals received from satellites, in which a digital composite of the signals received from a plurality of satellites is formed at a first point, the digital composite is processed to measure the carrier phase of the signal from each of the plurality of satellites to derive computer data, and said computer data are combined with data derived from measurements of signals received from the same plurality of satellites at another point, to determine position data.

Abstract: A radar system (25) includes a transmitter (42), receiver (48) and a phased array antenna (28) composed of a plurality of subarrays (26). The transmitter is interconnected with certain laterally located subarrays (34, 36, 38, 40) of the antenna and other centrally disposed subarrays (30, 32). The subarrays (26) are interconnected via beam formers (46) to a multi-channel receiver (48) providing a radar system having multiple beams with enhanced sidelobe suppression. Another version steers the transmit beams by applying linearly varying phase functions (56) combined with fixed increasing or decreasing phase functions (57)to antenna array radiators(55).

Abstract: In a method to resolve ambiguities in a phase measurement for application in radar interferometry, a frequency estimation method is used, starting from conjugate complex products of pairs of adjacent pixels in an interferogram. The resolution of these products is subsequently reduced through successive addition or averaging, after which the differential phase of adjacent resolution levels is determined in each resolution level. The sum of the phase differences yields the estimated value for the phase gradient which is then used in a known method, such as the least-squares method, to reconstruct the absolute phase, thus resolving the phase ambiguities. The method according to the invention serves to resolve phase ambiguities in radar interferograms without producing the known distortions produced by the existing methods. The method is also robust at low coherence values as they occur in repeat-pass interferometry where the existing methods fail.

Abstract: An apparatus for reducing the computational requirements for resolving ambiguity in interferometer measurements where the interferometer elements are arranged arbitrarily. Each of a plurality of interferometer elements each measures the phase of the incoming electromagnetic signal. The interferometer elements are each separated by lengths defined as baselines, which are sorted and processed in ascending order. Following initialization, for each baseline (92, 108), the phase measurements of the next baseline (92, 108) to be processed are estimated. If the measured phases (94-100, 110-118) of the next baseline (92, 108) falls within a predetermined range (104, 106) of the estimated phases, the phase is retained for estimating the phases of the next baseline. After a sufficient number of baselines have been processed, the angle of the incoming electromagnetic signal may be determined in accordance with the retained phases.

Abstract: A method of computing and correcting phase errors due to atmospheric turbulence in a dual-antenna multiple-pass synthetic array radar (SAR) interferometer system. The method improves topographic mapping accuracy at very long ranges. The method computes an atmospheric correction from the residual phase difference between a two-pass interferometer output (containing atmospheric phase errors) and a dual-antenna single-pass interferometer output (for which atmospheric phase errors cancel because the two channels are collected simultaneously). The residual phase measured in a single resolution element is then filtered by averaging over an area of many resolution elements, typically on the order of several thousand resolution elements. This exploits the long correlation distance of the atmospheric phase errors to reconstruct the dominant low-frequency part of the error spectrum. In addition, unwrapping the phase of the output of the complex Wiener filter produces an atmospheric turbulence measurement map.

Abstract: A horned interferometer antenna apparatus has parallel plates spaced apart and rigidly connected together by a separator. In the space between the parallel plates is a plurality of antenna elements. The parallel plates each have a free edge which diverge from the other free edge defining an aperture for receiving electromagnetic waves. The horned interferometer antenna apparatus has enhanced directivity and is used for passive radio direction finding. An interferometer system comprises a horned interferometer antenna apparatus, a multi channel receiver and a phase comparator. The interferometer system measures the angle of arrival of an incident electromagnetic wave or signal based on the phase difference between the signal as received by the antenna elements of the horned interferometer antenna apparatus.

Abstract: The virtual interferometer is an improved method for generating multiple ultaneous transmit beams as effected by a phased array radar. The technique is particularly suited to a solid state active radar array having a transmit/receive (T/R) module that is located at each radiating element. Potential applications to radar systems include environments such as air traffic control in which wide area surveillance with high search rates may be required. With multiple simultaneous beam generation coupled with parallel receiver beamformers and processors, such a radar system could support large volume searches while preserving the narrow beam characteristics by using the full aperture for generation of each of the multiple beams. The multiple simultaneous beams are generated by applying a particular phase shift at each radiating element, with no requirement for amplitude modulation.

Abstract: An interferometric Synthetic Aperture Radar (SAR) system having a special-purpose processor to integrate motion compensation, interferogram coregistration, and a spectral shifting for optimal interferogram correlation together to achieve efficient, accurate, and robust three-dimensional imaging. A simple radar mapping coordinate system is implemented in the present invention to enhance the overall image processing and in particular to improve the accuracy and efficiency. The present invention substantially improves the fidelity and efficiency of phase unwrapping by incorporating phase-bootstrapping process, a correlation filter, and other processes. Absolute phase determination is implemented without known ground references by two proposed techniques employing cross-correlation of sub-patches to generate a number of estimates within a patch and weighting correlation processes.

Abstract: A method for use with a long baseline interferometer that unambiguously estimates the angle of arrival of an RF agile signal produced by an emitter. The angle of arrival estimate provided by the method may be used to resolve phase ambiguities inherent in the long baseline interferometer, thereby providing for the unambiguous estimation of the angle of arrival of the RF signal from the emitter. The RF agile signals processed to determine the phase thereof. The phase information contained in the energy radiated by the emitter is then processed to estimate the angle of arrival of the energy. The phase information contained in the RF agile signal is processed using the equations .phi.=(2.pi.fL/c) sin .theta., and .delta. sin .theta.=(c/2.pi.fL).delta..phi., where the phase (.phi.) is measured to a given error (.delta..phi.) to determine the direction of arrival (.theta.) of the energy radiated by the emitter.

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.

Abstract: A retransmitted Ground Positioning System (GPS) using retransmission of a GPS signal in combination with an interferometer for determining the angular deviations of an aircraft relative to a landing site in both vertical and horizontal planes, by using the accumulated phase of the GPS carrier signal. The system includes an aircraft and a landing site, wherein a first unit comprising one of the aircraft and the landing site includes a GPS retransmitter for retransmitting GPS signals to a second unit comprising the other of the aircraft and the landing site, which includes a GPS receiver/computer two spaced apart GPS antennas mounted on a rotating frame, the plane of rotation of which is normal to the landing strip. In a first general configuration, each GPS antenna in the interferometer comprises a GPS receiving antenna and a GPS transmitting antenna, and an amplifier connecting the GPS receiving antenna with the GPS transmitting antenna, and the aircraft includes a GPS receiver/computer.

Abstract: A processing method that processes interferometer data to provide for rejection of multipath signal returns from an emitter and computes an improved estimate of the relative angle between the emitter and an interferometer. The present processing method comprises the following steps. Interferometric data is gathered that comprises complex signal amplitudes derived from the emitter at a plurality of emitter angles relative to the interferometer. The complex signal amplitudes derived at each of the plurality of emitter angles are processed by maximizing a predetermined log likelihood function corresponding to a natural logarithm of a predetermined probability density function at each of the plurality of emitter angles to produce a plurality of maximized log likelihood functions. The improved estimate of relative angle between the emitter and the interferometer is made by selecting the emitter angle corresponding to an optimally maximized log likelihood function.

Abstract: An AMTI radar employs a dual cancellation format to cancel the clutter in the radar returns received by the apertures of an interferometric radar antenna. Angle information generated on a first pass through the cancellation unit and the detection processor is recalculated in a second pass. Only those range doppler cells identified during the first pass as containing moving targets are used in the second angle calculation thereby enhancing the accuracy of this second angle measurement. This three-aperture system derives four data sets, L(t), C(t-.tau.), C(t) and R(T-.tau.) which represent samples taken over multiple pulse repetition intervals for each range interval or bin of interest. Fast Fourier transforms change the data sets into the frequency domain and phase compensations for the data sets are calculated in a triple interferometric signal calibration unit.

Abstract: An AMTI radar employs a dual cancellation format to cancel the clutter in the radar returns received by the apertures of an interferometric radar antenna. The three-aperture antenna presents the radar returns to three receivers which demodulate the returns to a complex in-phase signal I and a quadrature signal Q which are sampled at a pulse repetition interval at all ranges of interest. After conventional motion compensation four data sets are derived from the returns of the three apertures, L(t), C(t-.tau.), C(t) and R(T-.tau.) which represents samples taken over multiple pulse repetition intervals for each range interval or bin of interest. Fast Fourier transforms change the data sets into the frequency domain and phase compensations for the data sets are calculated in a triple interferometric signal calibration unit.

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

Abstract: The method provides the capability to estimate the angle-of-arrival (AOA) of radar pulses with respect to a ground or airborne based platform. It utilizes a spectral estimation technique which extracts the periodic properties of radar signals whose time-of-arrivals (TOAs) have been tagged by an Electronic Warfare receiver. The method can be used in a multiple signal environment and can separate and individually measure AOA of emitters that are spatially very close but have incommensurate Pulse Repetition Intervals (PRIs).

Abstract: A transponder location and tracking system having a phased array antenna mounted at a toll collection station includes a plurality of antenna array elements for receiving a signal from a transponder mounted on a vehicle and for providing a plurality of antenna element electrical signals. A plurality of phase detectors are provided for comparing the phase of the electrical signals to provide a plurality of phase difference signals. A plurality of angle-of-arrival calculation processors is provided for converting the phase difference signals to spatial signals to define the angles-of-arrival of the vehicle transponder signal. A position calculation processor is included for providing an output signal representative of the location of the vehicle in response to the defined angles-of-arrival. In a preferred embodiment, the transponder location and tracking system includes a plurality of receiver processing devices for amplifying and filtering the electrical signals from each antenna element.

Abstract: In a radio-frequency radar system, a radar antenna (12) irradiates a region to be monitored, and antenna elements (14a-p) arrayed irregularly about a mobile platform (10) receive the resultant echo signal, which mixers (18 and 21) translate in frequency, coherently with the transmitted signal, to a lower frequency, at which a sample-and-hold circuit (24) can sample it. A beam-forming operation is performed on the sample signals by employing coefficients that have been computed from calibration readings taken by the elements mounted on the platform. The beam signals resulting from numerous successive transmitted pulses are then integrated coherently to produce an output.

Abstract: The installation comprises a certain number of measuring stations, represed here as three in number referenced respectively 1, 2 and 3, equipped respectively with antennae I.sub.1, I.sub.2, I.sub.3, which are connected by transmission lines L.sub.1, L.sub.2 and L.sub.3 to a central data acquisition unit 4, itself connected to a real time data processing unit 5. The central unit 4 comprises receiving means, means for sorting and associating the data and means for momentary storage of the sorted and associated data.

Abstract: A radar system for tracking a plurality of individual objects that form a cluster. The system comprises means for producing in real time reference information indicative of the position of a reference point associated with the mean position of the objects, and means for producing in real time displacement information indicative of the relative position of each object with respect to the reference point. The system may handle a transmitter, and the means for producing the displacement information may include a interferometer system comprising a central receiver, a pair of first satellite receivers positioned on opposite sides of the central receiver along a first axis that passes through the central receiver, and a pair of second satellite receivers positioned on opposite sides of the central receiver along a second axis that passes through the central receiver and that is inclined with respect to the first axis.

Abstract: An emitter location system includes a single carrier based first and second short baseline interferometers, and a long baseline interferometer operatively connected to a computing means. The computing means includes a three level processor. The short baseline interferometers provide phase measurements for level one combination into total phase measurements and estimates of the angle of incidence of the incoming electromagnetic energy. After test for acceptance, the estimated angle of incidence is passed for level two processing which includes the simultaneous processing of the estimated incident angle with the phase measurement of the long baseline interferometer for error correction to provide an improved estimated incident angle. After test for acceptance, the improved angle of incidence measurement is passed for determining the angle of the incident wave for level three processing.

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 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.