Abstract: Apparatus and methods for multi-antenna wireless communication are provided. In an aspect, one or more input ports of a first layer two-dimensional (2D) Butler matrix are selected for communication of one or more streams by an array antenna over one or more beams. A control signal is applied to a control input pin of a first layer to second layer switch configurable, based on the control signal, to selectively connect first layer output ports of the first layer 2D Butler matrix to at least a subset of second layer input ports of a second layer 2D Butler matrix. One or more streams are then transmitted or received by an array antenna over one or more beams, wherein the array antenna includes a plurality of antenna elements, wherein each one of the plurality of antenna elements is associated with one output port of the second layer 2D Butler matrix.

Abstract: There is provided a radar device configured to detect a target by executing signal processing on the basis of a transmission wave and a reflection wave of the transmission wave reflected on the target. An antenna unit having a plurality of antennas arranged in a vertical direction. A calculation unit configured to calculate vertical azimuths of the target on the basis of the reflection waves with respect to the transmission waves transmitted from each of the antennas, and to accumulate calculation results. An estimation unit configured to calculate moving average values of maximum values of the vertical azimuths on the basis of the calculation results accumulated by the calculation unit, and to estimate the moving average values of the maximum values, as a height of the target.

Abstract: A wireless receiver includes an antenna array and processing circuitry. The antenna array receives radio waves from a radio wave radiator to output received signals. The processing circuitry calculates similarity indices based on (1) a first eigenvector corresponding to a largest eigenvalue of a covariance matrix of each of the received signals, and (2) a degree of similarity between the first eigenvector and a steering vector of a single wave, estimates angles of arrival of the received signals, and determines an output angle of arrival from the estimated angles of arrival of the received signals.

Abstract: A radar apparatus (5) for detecting multipath signal propagation when determining an elevation angle of an object, comprising an antenna array with which the radar apparatus is arranged to form at least three separate antenna beams (11, 12, 13) comprising a first antenna beam (11) having an angle of elevation above horizontal, and a separate second antenna beam (12) having an angle of elevation at or above horizontal which is less than that of the first antenna beam, and a separate third antenna beam (13) having an angle of elevation below horizontal. The apparatus is arranged to transmit radio pulses from the antenna array; to receive return radio signals within the first, second and third antenna beams; to calculate a measure of the magnitude of a return radio signal received within the third antenna beam using all of said received radio signals collectively; and, to detect multipath signal propagation using said measure.

Abstract: Systems and techniques relating to angle of arrival (AoA) reverse locationing include: transmitting, by a first wireless device to a second wireless device, one or more reverse tracking service discovery messages via a wireless communication link; receiving, at the first wireless device from the second wireless device, one or more response messages associated with the one or more reverse tracking service discovery messages, wherein the one or more response messages comprise (i) information indicating that the second wireless device is enabled for reverse tracking, and (ii) angle of arrival (AoA) information based on AoA calculations performed by the second wireless device; and determining, by the first wireless device, a location of the second wireless device based on the received AoA information.

Abstract: A phased array radar system comprises an array antenna including a plurality of selectively controllable transmit/receive (T/R) modules. One or more computer processors and associated memory devices are provided in communication with the plurality of T/R modules. The control processor is configured to cause the transmission of a first plurality of radio frequency (RF) pulses from a first portion of the array antenna, wherein the first plurality of pulses comprise at least two pulses having distinct center frequencies. A second plurality of RF pulses are transmitted from a second portion of the array antenna, wherein the second plurality of pulses comprise at least two pulses having distinct center frequencies. Received return signals originating from the first and second plurality of transmitted pulses are non-coherently integrated prior to the performance of target detection operations.

Abstract: Aspects of the disclosure provide for an antenna system. The antenna system includes a main reflector, a phased array feed, and a mechanical steering system. The phased array feed is configured to receive and/or transmit signals reflected off the main reflector and to electronically steer a transmitted signal on a first axis. The main reflector and the phased array feed are both attached to the mechanical steering system, and the mechanical steering system is configured to move the transmitted signal along a second axis.

Abstract: A method of open-switch fault detection in a two-level voltage source power converter comprises the steps of: i. acquiring the waveforms of three-phase alternating current of the two-level voltage source power converter; ii. calculating at least a first time derivative of each acquired waveform; and iii. using the at least first time derivatives to determine whether an open-switch fault is present in the two-level voltage source power converter.

Abstract: Disclosed is a system, apparatus, and method for RF management using network-device-to-network-device channel estimation and standard beamforming techniques. The exemplary method comprises: obtaining a first information corresponding to a first device that is a target device for transmitting at least one of a plurality of wireless signals by a network device; obtaining a second information corresponding to a second device that is to be avoided by propagation of any wireless signals transmitted by the network device; computing a radiation pattern for transmitting the plurality of wireless signals based at least on the first information associated with the first device and the second information associated with the second device; and transmitting the plurality of wireless signals based on the radiation pattern.

Abstract: A standard wafer is provided including a substrate; a first layer of semiconductor material formed on the substrate; a bar formed over the first layer of semiconductor material with an interlayer interposed therebetween; and a first sidewall spacer and a second sidewall spacer formed on the opposite sides of the bar respectively, in which the bar and the first layer of semiconductor material are formed of a same semiconductor material, and the interlayer interposed between the first layer of semiconductor material and the bar is formed of a first oxide, and the first sidewall spacer and the second sidewall spacer are formed of a second oxide. A corresponding fabrication method of the standard wafer is also provided.

Abstract: An amplifier circuit is disclosed. In one embodiment, the amplifier circuit includes an input configured to receive an input signal. The amplifier circuit further includes an amplifier connected to the input that is configured to receive the input signal and generate a modulated input signal based on the input signal and one of a first amplification level and a second amplification level. The amplifier comprises a first transistor configured to receive the input signal and a second transistor connected in cascode with the first transistor. The amplifier circuit further includes a switching component configured to switch the amplifier between the first amplification level and the second amplification level. The amplifier circuit still further includes an output connected to the amplifier and configured to output the modulated input signal.

Abstract: A method and apparatus for reducing transponder responses to reflected signals utilizes data in an interrogator message to confirm that if two interrogations are received within a predetermined period of time and if the two interrogator signals correspond to a side lobe followed by a reflected main beam signal, the presence of multipath reflection can be correctly identified and the reply to the main beam interrogation can be suppressed.

Abstract: The present invention is directed to a system and method for the identification of a target object in PCL radar applications. The disclosed embodiments describe the systems and methods used in the identification of a target object from the collection of data representing specific target object features, such as velocity, altitude, fuselage length, wing length, or wing sweepback angle, and the comparison of selected target object features with a database of known aircraft features. The present invention also provides for the calculation of feature dimensions, such as the fuselage length, wing length, or wing sweepback angle from measurements associated with a peak signal lobe as a function of a bistatic aspect angle.

Abstract: The present invention relates to a method for determining the position notably the elevation of a target flying at very low altitude. An electromagnetic detection system extracts the measurement of the elevation on the basis of the amplitude of the interference signal produced by a signal emitted directly by the target and by a signal emitted by the target towards the ground then reflected by the ground towards the radar. Embodiments of the invention can notably be used within the framework of the guidance of drones in the final landing phase.

Abstract: A method of determining an angle with a beam to terrain for a terrain avoidance system includes receiving first data associated with first returns associated with a first portion of an antenna. The method further includes receiving second data associated with second returns associated with a second portion of the antenna, wherein the first portion is different than, intersects, or includes the second portion. The method further includes determining the angle to terrain using the first data and second data.

Abstract: A method and device for object detection in the case of a vehicle equipped with an object-detection system, the object-detection system emitting electromagnetic radiation and receiving radiation reflected off objects within the detection range, and the radiation reflected off a detected object, which was additionally reflected off an object extending along the roadway, is analyzed. The analysis consists of a plausibilization in which the directly measured object reflections are verified using the indirect object reflections, or in that the analysis consists of utilizing the indirect object reflections for the further object detection if reflections from a previously detected object are no longer measurable.

Abstract: Apparatus and a method utilizing correlation interferometer direction finding for determining the azimuth and elevation to an aircraft at long range and flying at low altitudes above water with a transmitting radar while resolving multipath signals. The signals from the radar are received both directly and reflected from the surface of the water using horizontally polarized and vertically polarized antenna arrays, are digitized and are stored in separate covariant matrices. Eigenvalues for the eigenvectors of the matrices processed on signal samples recorded on horizontally polarized X arrays are compared to the eigenvalues for the eigenvectors of the covariance matrices processed on signal samples recorded on vertically polarized X arrays. Incident field polarization is associated with the antenna array measurements that yield the strongest eigenvalue. The eigenvector and eigenvalues for the strongest signal are selected and used for subsequent signal processing.

Abstract: A monopulse radar operating at low angles of elevation (LOE) receives returns from a target by a direct path and by a path including a reflection from that portion of the Earth's surface lying between the radar and the target. The surface-reflected signal tends to cause errors in the estimate of the elevation of the target. A radar system directs at least upper and lower overlapping beams at LOE toward the target for receiving returns. The upper and lower beams may be sequential or simultaneous. Real and imaginary portions of the sum (?) and difference (?) signals are generated for each beam. The monopulse estimates of elevation ê derived from the real portion of the ? and ? signals are processed to produce correction signals for upper and lower beams. Each correction signal is weighted and summed to correct the estimate of elevation.

Abstract: Apparatus and a method utilizing correlation interferometer direction finding for determining the azimuth and elevation to an aircraft at long range and flying at low altitudes above water with a transmitting radar while resolving multipath signals. The signals from the radar are received both directly and reflected from the surface of the water using horizontally polarized and vertically polarized antenna arrays, are digitized and are stored in separate covariant matrices. Eigenvalues for the eigenvectors of the matrices processed on signal samples recorded on horizontally polarized X arrays are compared to the eigenvalues for the eigenvectors of the covariance matrices processed on signal samples recorded on vertically polarized X arrays. Incident field polarization is associated with the antenna array measurements that yield the strongest eigenvalue. The eigenvector and eigenvalues for the strongest signal are selected and used for subsequent signal processing.

Abstract: Apparatus and a method utilizing correlation interferometer direction finding for determining the azimuth and elevation to an aircraft at long range and flying at low altitudes above water with a transmitting radar while resolving multipath signals. The signals from the radar are received both directly and reflected from the surface of the water using horizontally polarized and vertically polarized antenna arrays, are digitized and are stored in separate covariant matrices. Eigenvalues for the eigenvectors of the matrices processed on signal samples recorded on horizontally polarized X arrays are compared to the eigenvalues for the eigenvectors of the covariance matrices processed on signal samples recorded on vertically polarized X arrays. Incident field polarization is associated with the antenna array measurements that yield the strongest eigenvalue. The eigenvector and eigenvalues for the strongest signal are selected and used for subsequent signal processing.

Abstract: The communication system utilizes transmitters that provide communication transmissions having deterministic data. Receivers of the system have the digital processing capability for correlating received transmission reflections of the deterministic data amongst the receivers, the reflections of the deterministic data being from objects within the transmission range of a respective transmitter. The correlating includes utilizing relatively weak multipath signals of the transmission reflections and the superimposition of external data therewith to provide a resulting data base of range reflections. The range reflections are provided to others of said plurality of receivers for processing to derive the environment and the locations and movements of objects without the use of a specific interrogation signal, thereby providing situational awareness.

Abstract: Analysis of electromagnetic (or acoustic) multipath propagation inventively focuses upon the transmitter-to-target propagation (transmitted propagation reaching target via both direct pathway and forward scattered pathway) and the target-to-receiver propagation (re-transmitted propagation reaching receiver via both direct pathway and forward scattered pathway). Transmitter-to-target propagation is calculated using conventional multipath modeling technique. The target's overall scattered field is calculated using the calculated transmitter-to-target propagation in conjunction with qualitative electromagnetic/acoustic target information. Target-to-receiver propagation is calculated using conventional multipath modeling technique and/or the reciprocity principle as applied to the calculated transmitter-to-target propagation.

Abstract: A bistatic radar has a radar transmitter at a first location on a moving platform having a motion and a radar receiver at a second location, remote from the first location. The transmitter illuminates a target along an indirect path with an encoded radar signal. The target reflects the encoded radar signal to the radar receiver. The transmitter concurrently provides the encoded radar signal to the radar receiver along a direct path. The encoded radar signal is radiated at a start time from a central reference point, and contains the first location, the pulse start time, the central reference point and the motion of the moving platform. Bit synchronization codes are also included. The radar receiver receives the encoded radar signal from the radar transmitter along the direct path during a first time interval, and the same encoded radar signal reflected from the target along the indirect path during a second time interval.

Abstract: Signals including a plurality of components representing a phase rotation between antenna elements by combining signals, which have arrived through each path of a first to an m-th paths, for every antenna are generated in RAKE combining sections 104-1 to 104-n; one angle spectrum is obtained in one direction-of-arrival estimation section 105 provided in each communication terminal, using the signals generated in the RAKE combining sections 104-1 to 104-n; and a plurality of directions-of-arrival are estimated en bloc by detecting a plurality of peak positions on the angle spectrum.

Abstract: Analysis of electromagnetic (or acoustic) multipath propagation inventively confines the assessment of multipath propagation to a “surface interactive region” (“SIR”), intermediate the target and transmitter and/or the target and receiver. The down range time of the propagation, translatable to range distance, is related to error associated with such restriction. A SIR scope is selected commensurately with acceptable error. Jointly disclosed (practicable therewith or thereapart) is inventive focus upon the transmitter-to-target propagation (transmitted propagation reaching target via both direct pathway and forward scattered pathway) and the target-to-receiver propagation (re-transmitted propagation reaching receiver via both direct pathway and forward scattered pathway). Transmitter-to-target propagation is calculated using conventional multipath modeling technique.

Abstract: The invention concerns a passive radar receiver with an array of antennas for a OFDM received signal comprising frames of symbols each emitted on coded orthogonal carriers. After formatting received signals into digital symbols, dummy signals from dummy OFDM emitters at different distances from and in different directions relative to the receiver are generated and added to the signals picked up by the antennas. The modified received signals are filtered by means of inverse covariance matrices in order to eliminate at least unwanted zero Doppler effect signals and to provide an isotropic reception diagram without blind sector of direct path being generated and by detecting mobile targets along the direct path.

Abstract: A method for determining the position of at least one second transmitting and receiving device (3) in respect of a first transmitting and receiving device in a passive access control system operating in the GHz range, comprising the steps of using a radar method, wherein signals (f1, f2) are received in the first transmitting and receiving device on the left-hand side and right-hand side of a modulation frequency (fmod), determining the distance of two signals (f1, f2) closest to the left-hand side and right-hand side modulation frequency (fmod) wherein the distance is proportional to the distance between the first transmitting and receiving device and at least one second transmitting and receiving device (3), so that multipath propagations are not taken into consideration.

Abstract: A mobile communication base station determines the oncoming direction of a radio wave with a simple arrangement and transmits a narrow angle beam in this direction. Received signals from a pair of wide angle beam antennae 21-1 and 21-2 having an equal configuration and a common orientation and which are located close to each other are fed to a direction finder receiver 22 and a communication receiver 15. By utilizing the fact that the both received signals have a coincident amplitude, a phase difference between the received signals is detected. The oncoming direction of the received radio wave (or the direction of a mobile station) is determined on the basis of the phase difference. A beam switcher 12 is controlled so as to connect a transmitter 13 to a narrow angle beam antenna (one of 11-1 to 11-4) which is directed in the oncoming direction thus determined.

Abstract: A positioning apparatus and method for accurately determining a current position of a mobile station. The current position of the mobile station is determined utilizing radio waves arriving from a plurality of base stations installed in a communication area. For calculating a propagation range of a radio wave arriving from each base station, error correction processing is performed using a predetermined error correction coefficient previously calculated by measuring a radio wave propagation situation around each base station to estimate a propagation range of a direct wave within incoming radio waves. The current position of the mobile station is determined using the estimated propagation range and the positions of the respective base station.

Abstract: The invention concerns a passive radar receiver with an array of antennas for a OFDM received signal comprising frames of symbols each emitted on coded orthogonal carriers. After formatting received signals into digital symbols, dummy signals from dummy OFDM emitters at different distances from and in different directions relative to the receiver are generated and added to the signals picked up by the antennas. The modified received signals are filtered by means of inverse covariance matrices in order to eliminate at least unwanted zero Doppler effect signals and to provide an isotropic reception diagram without blind sector of direct path being generated and by detecting mobile targets along the direct path.

Abstract: A method of compensating for atmospheric effects to detect the actual location of low elevation objects using near horizon radar to detect an object which utilizes a preexisting satellite, wherein the location of the satellite is known. The method includes a step of providing a radar site, a first receiver structured to receive a signal from the satellite, and known location data for the satellite then positioning the first receiver near the radar site. The first receiver is utilized to receive a signal from the satellite when the satellite is at a low elevation. The bending angle can then be determined by comparing the apparent location data of the satellite as determined by the first receiver to the known location data of the satellite. This data may also be combined with weather data is used to determine a three dimensional refractivity model. Once the bending angle of the atmosphere is determined, the radar is used to detect the apparent location data of a low elevation object.

Abstract: A technique for estimating the position of an object from sensor measurements in the presence of multipath conditions is disclosed. In one aspect, the technique includes a position estimator comprising a signal filter, a multipath detector, and a multipath bias estimator. The signal filter is capable of receiving a sensor measurement and generating a measurement noise variance estimate and a position estimate therefrom. The multipath detector is capable of applying a dynamic threshold against the measurement noise variance estimate to determine whether a multipath condition exists. And, the multipath bias estimator is capable of generating a correction for multipath induced measurement bias error from a measurement noise variance estimate for application upon determining that a multipath condition exists.

Abstract: A method for determining the position of at least one second transmitting and receiving device (3) in respect of a first transmitting and receiving device in a passive access control system operating in the GHz range, comprising the steps of using a radar method, wherein signals (f1, f2) are received in the first transmitting and receiving device on the left-hand side and right-hand side of a modulation frequency (fmod), determining the distance of two signals (f1, f2) closest to the left-hand side and right-hand side modulation frequency (fmod) wherein the distance is proportional to the distance between the first transmitting and receiving device and at least one second transmitting and receiving device (3), so that multipath propagations are not taken into consideration.

Abstract: This present invention advantageously eliminates the critical deficiencies of current multipath interferometer processing demonstrated in field testing. In particular the present invention substantially improves AOA estimation accuracy and reliability when utilizing super resolution algorithms. The present invention also overcomes the data-gap drawback of data editing methods, especially for emitters at low elevations. The present invention does this by detecting phase processing errors and substituting correct AOA estimates for the corrupt ones. In the preferred implementation, the detection and substitution time extends only slightly the super resolution or data editing processing time. By thus requiring little additional processing time, the present invention allows the interferometer to output accurate angle estimates at the receiver's emitter-revisit rate for all emitter-array geometries and signal polarizations.

Abstract: A system and method for mitigating co-channel interference is disclosed. A radar system detects targets from received signals at an antenna array. The received signals include direct signals and target signals transmitted from remote transmitters. An antenna array receives the signals. A signal processing system is coupled to the antenna array to perform processing operations on the received signals. The processing system includes a primary cancellation component and a secondary cancellation component. A primary illuminator signal is cancelled from the received signals by the primary cancellation component. An adaptive beam former obtains a secondary illuminator signal from the received signals. A reference regenerator regenerates the secondary illuminator signal. An adaptive cancellation filter removes noise from the secondary illuminator signal. The secondary cancellation component mitigates co-channel interference by canceling the secondary illuminator signal from the received signals.

Abstract: A method and system for identifying the locations of plural targets lying within a main beam of a monopulse antenna including four ports for generating sum, elevation difference, azimuth difference and double difference signals. The method comprises the steps of forming a monopulse ratio matrix from the sum, elevation difference, azimuth difference and double difference signals; and determining eigenvalues of the monopulse ratio matrix. These eigenvalues are then used to determine the angular locations of the plural targets. Preferably, the eigenvalues are determined by performing an eigenvalue decomposition of the monopulse ratio matrix to generate eigenvalues, and the angles of the targets may be determined from the eigenvalues by the use of a look-up table.

Abstract: Objects of interest are detected which are below the horizon and which emit or are the cause of pressure wave fronts. By emitting radar pulses that interact with the pressure wave fronts that appear above the radar horizon and then by analysis of the detected echo signals in the range bins, the existence of a pressure wave front can be determined. Then, it is evaluated if this pressure wave front indicates the presence of an object of interest or not. The transmitted radar pulses in relation to the detected echoes can be used for identifying the object of interest. The emitted radar pulses may have a wavelength which is a multiple of the expected wavelength of the pressure wave fronts.

Abstract: Upon receiving a radar electric wave from a search radar, a radar transponder according to the present invention generates a trigger signal in response to the reception of the radar electric wave. In response to only the trigger signal, the radar transponder starts to generate sweep signals, and continues to generate sweep signals until a stop condition based on an external factor such as stop of power supply or the like is satisfied. Accordingly, the response electric wave can be received with a high probability in the search radar.

Abstract: The direct path of a radio signal from transmitter to receiver is frequently interfered with by reflections of the signal from stationary and moving objects. This is called multipath noise. This invention utilizes a new adaptive filter technique to reduce multipath noise. A nonlinear least squares method measures the delay, Doppler shift and amplitude of the multipath due to each object and subtracts a very accurate reconstruction of each multipath signal from the noisy signal. If an object is a target, its range, range rate and magnitude is got from the measured multipath delay, Doppler shift and amplitude. Position and velocity of the target can be obtained by geometric triangulation with multiple transmitters. Target angle can be measured by the relative phase of the corresponding filter coefficients across multiple antennas. The system can be used on a surveillance aircraft to cancel ground reflections and measure targets.

Abstract: A tracking method for a signal echo system, including generating a plurality of gates for respective propagation modes on the basis of a target state prediction for a dwell time, and generating a target state estimate for the dwell time on the basis of target measurement points which fall within the gates.

Abstract: The invention relates to the processing of the multiple paths in an interrogator station which, in response to a salvo of interrogations, receives responses in the form of pulses. The station comprises at least two reception channels. The responses to each interrogation of one and the same salvo are classified by order of appearance. A value of dispersion of the energies is estimated, for each channel and each salvo, on the responses having the same classification. Since the first classified response is, by assumption, considered to have arrived by a direct path, the following responses will be eliminated, on the grounds that they have been received after passing through multiple paths, if their values of dispersion of energy on the two paths are not equivalent to those of the first response.

Abstract: A method and apparatus for detecting the presence of multipath interference within a radar receiver disposed to form sum (.SIGMA.) and difference (.DELTA.) signals by time-sampling a target return signal is disclosed herein. In accordance with this method there is formed a sequence of complex conjugates (.SIGMA.*) of the sum signals (.SIGMA.). Each of the .SIGMA.* signals is multiplied with an associated one of the .DELTA. signals so as to form a time-sampled sequence of .SIGMA.*.DELTA. signals. A power spectrum representation of the time-sampled sequence of signals .SIGMA.*.DELTA. is then generated, wherein the presence of selected spectral components within the .SIGMA.*.DELTA. power spectrum indicate the existence of multipath interference within the radar receiver. In a particular implementation the .SIGMA.*.DELTA. power spectrum representation is quickly and reliably determined by performing a Fast Fourier Transform (FFT) operation upon the time-sampled sequence of .SIGMA.*.DELTA. signals.

Abstract: The present invention provides a wireless communication system which employs Butler matrix combiners and circuit switching at transmitter and receiver antenna arrays to provide directive beamwidth capabilities. Such narrow beamwidths permit the communication system to determine and select the transmission path having an optimum signal quality. The antenna arrays are integrated in a multilayer construction which reduces power consumption, increases the coverage range, improves the efficiency of the antenna array, and which has lower fabrication costs.

Abstract: The attitude of a body 12 is determined, or refined, by illuminating it with a direct beam and one or more indirect beams which are reflected from a scattering surface SS, all of the beams being radiated from the same or adjacent sources. The directions of arrival of the beams are determined to allow the attitude to be determined or refined.

Abstract: A multiple-hypothesis, multipath-matched filter (10) is disclosed for use in combining multipath components of transmissions between, for example, an aircraft (12) and aircraft (14) through a multipath environment (16). Rather than sensing the characteristics of the environment and adjusting the multipath components accordingly, the disclosed filter is designed on the basis of several hypotheses concerning the differences in the path lengths traversed by the various multipath components, as well as the phase shift introduced into each. In a preferred arrangement, the path length differences .DELTA.R are assumed to be some integer multiple of the range gate setting .delta.R of a transmitter/receiver (28) included on the aircraft. The phase shifts .psi. are assumed to be either 0.degree. or 180.degree..

Abstract: A method of operating a radar system is shown to include the steps of transmitting a plurality of signals, each signal having a different frequency, and receiving, if existing, a corresponding return signal for each one of the plurality of signals. The method further includes ascertaining an angle off beam cross-over of a target from each existing return signal, selecting the angle off beam cross-over having the largest magnitude, ascertaining a reduction factor appropriate for the selected angle and reducing the magnitude of the selected angle by the reduction factor. With such an arrangement, a radar system is provided having improved elevation measurement accuracy.

Abstract: In a method for tracking a radar target the imaginary part of the complex elevation error signal is utilized and the value of the complex elevation error signal is calculated for a plurality of frequencies in a repeated sequence. The value change between the different frequencies is used for determining the position within an unambiguous interval and the values calculated at the zero crossing are utilized as measure of the inclination which in turn is compared with inclinations calculated for zero crossings in a general case, whereby a single-valued (unambiguous) interval and position can be determined and thereby the associated elevation angle or target height can be calculated. The method is specifically useful for tracking at low height where multi-path propagation poses a problem in tracking according to known methods.

Abstract: A direction finding method and system for locating the direction of a transmission source based on an electromagnetic wave which is transmitted from the transmission source and is received by an antenna means at a receiving end apparatus. The transmission source transmits an angle-modulated wave. Meanwhile, the receiving end apparatus receives the transmitted wave, converts into electrical signals a beat frequency signal which is caused by direct and reflected waves contained in the received wave, and time-averaging the electrical signals, thus minimizing a angle error due to a multipass interference.

Abstract: A method for correction errors in radar systems that operate using a crossfeed principle (CFR), in which echo signals are directly received from flying objects, such as an aircraft. In particular, the present invention is used in connection with low-flying objects, in which radar signals are indirectly reflected from the surface of the earth to an antenna of the radar system. Correction terms are determined and weighted, using correction factors, so as to improve the capability of the crossfeed radar system to accurately determine the exact elevation of the flying object. The correction factors that are used to improve the accuracy of the radar system are based upon sea state numbers, or Beaufort numbers, which vary in relation to the shape and/or structure of the reflecting surface.

Abstract: Radar apparatus for determining the height of a low-elevation target, the target being illuminated by a transmitter (7) and an antenna (3) via a TR-switch (6). Electromagnetic radiation reflected directly by the target and indirectly by the target via the earth surface is received by the antenna (3) and processed in a sum receiver (9, 10, 11), connected via the TR-switch (6) to the antenna (3), into complex sum signals, and in a difference receiver (12, 13, 14), into complex difference signals. A signal processor (15), receiving the complex sum signals and the complex difference signals, is provided with an algorithm which determines the height of the target. The algorithm enables the determination of the target height while the antenna remains directed at the target.