Abstract: A method for calibrating the radar system includes the steps of: replacing stored statistically generated "average" error correction coefficients with error correction coefficients personal to a missile under test. More particularly, stored in the missile's memory are: (a) first personalized error correction coefficients generated in response to test signals produced internal to the missile and injected into a monopulse arithmetic unit for the missile's receiver/processor; and (b) a second set of personalized error coefficients generated in response to test signals external to the missile and injected through the missile's antenna to the receiver/processor. The missile includes a radio frequency (R.F.) energy test signal generator for performing a test during the missile's flight to determine "in-flight" personalized error correction coefficients. The test is performed in-flight by injecting the R.F.

Abstract: An architecture for remote calibration of coherent systems uses coherent reference and calibration signals that contain the relative amplitude and phase information desired in the calibration process. Circuitry extracts the relevant amplitude and phase information needed for the calibration while compensating for non-synchronized clocks and the effects of Doppler shifts due to relative motion of the transmitting and receiver platforms. The coherent detection architectures can be used effectively with any scheme designed to determine the relative amplitudes and phases of the signals emitted from the different elements of the phased array. These architectures are particularly applicable to coherent encoding calibration procedures that enhance the effective SNR by using coherent transmission of orthogonal transform encoded signals from N elements of the phased array.

Abstract: For the testing of radio navigation instruments by means of an automatic testing system controlling electric signal measuring and generating equipment, said instruments using radio navigation signals comprised of complex-shaped composite low-frequency signals modulating a high-frequency carrier wave, the method embodying the invention comprises the utilisation of standard signal generating equipment (11, 13, 14, 15) to generate primary low-frequency signals and a high-frequency carrier wave, the combining of these primary signals to obtain said composite low-frequency signals, and the modulation of the high-frequency carrier wave by the composite signals.

Abstract: An antenna test body for providing azimuth and elevation rotation having a rotating cylinder contained within said test body and an arc sector under the test body capable of providing elevation rotation. The test body provides a phase stationary center point under rotation of both azimuth and elevation.

Abstract: A sidelobe reduction benefit in a two-way pattern is accomplished when each attern (transmit or receive) has the same character as traditionally designed, but they differ in polarization. When polarization mismatch is included in the antenna pattern characteristic, the opposite sense of polarization in the sidelobe results in cancellation of signals between transmit and receive and, therefore, a net polarization loss or sidelobe level reduction in the combined two-way pattern. Polarization mismatch is accomplished by designing a separation distance between the transmitting elements and the corresponding receiving elements of the array. Choice of separation distance results in locating the region of perfect polarization mismatch in any desired angular direction.

Abstract: A near field planar wavefront generation method that uses a relatively small number (three to five) of transmitting antennas disposed a predetermined distance from an antenna array having a multi-wavelength aperture that is part of a system under test. The method creates a synthesized one-dimensional linear planar wavefront of radiation over at least ten wavelengths for testing the antenna array of the system under test. The planar wavefront is formed at a specific frequency and at predetermined distance from the transmitting antennas, typically in the range of from 100 to 200 feet. The transmitting antennas synthesize a plane wave with linear phase progression to simulate tilt variations. To achieve this, electromagnetic energy signals emitted by the respective transmitting antennas are amplitude and phase weighted to synthesize the one dimensional linear plane wave to produce a combined wavefront having a linear phase front across the aperture of the antenna array of the system under test.

Abstract: Novel test mounts are defined for a radar cross section testing apparatus that allows a supported object to be tested without interference from the test mount. This includes prescribing a diameter of about 0.61 wavelengths for a cylindrical test mount; maintaining a ratio for the test mount's characteristic dielectric constant and magnetic permeability of about one; and/or installing a frequency transposing apparatus to convert the frequency of radar pulses directed toward the test mount to off-frequency echoes.

Abstract: A radar module includes a high-frequency signal generator comprising upper and lower parallel conductive plates, at least one dielectric rod held between the parallel conductive plates, a metal diode mount held between the parallel conductive plates, a gunn diode member mounted on a side of the diode mount, and a printed-circuit board mounted on the side of the diode mount in covering relationship to the gunn diode member and having a bias supply circuit on its surface for supplying a bias voltage to the gunn diode member. One terminal of the gunn diode member extends through a through hole defined in the printed-circuit board, is exposed in the vicinity of the surface of the diode mount, and is connected to the bias supply circuit.

Abstract: Airplanes have transponders which receive and transmit signals to communicate information regarding the flight of the airplane. A transponder testing apparatus is integrated into the transponder and verifies that the transponders are operating in accordance to Federal Aviation Regulations.

Abstract: A method and apparatus for remotely calibrating a system having a plurality of N elements, such as a phased array system, is provided. The method includes generating coherent signals, such as a calibration signal and a reference signal having a predetermined spectral relationship between one another. The calibration signal which is applied to each respective one of the plurality of N elements can be orthogonally encoded using a unitary transform encoder that uses a predetermined transform matrix, such as a Hadamard transform matrix or a two-dimensional discrete Fourier transform matrix, to generate a set of orthogonally encoded signals. The set of orthogonally encoded signals and the reference signal are transmitted to a remote location. The transmitted set of orthogonally encoded signals is coherently detected at the remote location. The coherently detected set of orthogonally encoded signals is then decoded using the inverse of the predetermined encoding matrix to generate a set of decoded signals.

Abstract: The placement of repeater or base station antennas in an in-building or urban wireless RF communications network is optimized using field measurements. Test antennas are placed at a number of sites within the coverage area, and the signal from each test antenna is measured at different locations within the coverage area. The measurement allows the simulation of the coverage provided by different arrangements of antennas. An optimum arrangement can then be chosen. The optimum arrangement of antennas is chosen by maximizing a utility function that depends on the quality of the coverage within the area and on the cost of installing an arrangement. A database of architectural categories (building plans) and measurement results for each category is built by a method of the present invention. A new building is then matched to the closest component categories in the database, thus allowing the optimization of coverage in a coverage area without the measurement of signals from nest antennas in the new building.

Abstract: A system for use with aircraft having a collision avoidance system which employs i) two transponder systems each including two antennas and a selected one of two transponders and ii) a failure warning when a transponder system failure occurs, to permit the aircraft to take off when the failure warning is the result of only one antenna failure.

Abstract: A portable antenna control unit that operates a radar antenna and simulates arious control signals that are generated by a fire control radar. The antenna control unit can be interfaced to a standard commercial, portable computer, or it can be portable, stand-alone unit, manually controlled and easily transported to a test range. Both embodiments diagnose problems in an antenna radar system antenna without installing an entire radar system.

Abstract: A method and apparatus for remotely calibrating a system having a plurality of N elements, such as a phased array system, is provided. The method includes generating coherent signals, such as a calibration signal and a reference signal having a predetermined spectral relationship between one another. The calibration signal which is applied to each respective one of the plurality of N elements can be orthogonally encoded based on the entries of a predetermined invertible encoding matrix, such as a binary Hadamard matrix, to generate first and second sets of orthogonally encoded signals. The first and second sets of orthogonally encoded signals and the reference signal are transmitted to a remote location. The transmitted first and second sets of orthogonally encoded signals are coherently detected at the remote location.

Abstract: A method for determining the far field radar signature of relatively large and complex objects, like a fighter aircraft, and the facility to provide the data for the method. The method includes reflecting different frequencies of near field radar energy off of an object while translating the object in a radial direction with respect to the radar so the resulting radar return includes a moving signal representative of the radar return of the object and a stationary return representative of environmental clutter. The environmental clutter and R 4 amplitude variations caused by signal strength variations due to the different overall reflection distances during translation are removed from the radar signal. Multipath reflections may also be removed.

Abstract: A method to measure the far field antenna pattern of an experimental antenna on a smaller range than conventionally used. The basic innovation of the present invention is that the implementation is moved in straight line, toward or away from the antenna under test (AUT), and the measurements are taken while the AUT is rotated about its phase center in a manner that is synchronized with the radial probe.

Abstract: Detection means having thin wire electrodes that are placed on the outer surface of a radome that shelters an antenna used for transmitting and/or receiving intelligence in the form of radio waves, such as those microwave signals used in radar, especially radar that is used for a vehicle. The thin wire electrodes are placed on the radome surface in a way which will not change antenna characteristics. The electrodes measure the electrical resistance of the obstruction material, such as wet mud, that may find its way onto the outer surface of the radome during the operation of the vehicle and that may reduce the sensitivity of the radar's receiver so as to prevent it from recognizing otherwise discernable echo information. The detection means, upon detecting a predetermined electrical resistance of the obstruction material, provides a signal that is routed to the operator that is indicative that the radar performance may have degraded beyond an acceptable limit.

Abstract: A frequency surveillance method for monitoring background atmospheric noise evels in unoccupied channels in an operating frequency band of a high frequency communication system. In the method, the unoccupied channels are scanned a number of times to obtain analogue signals. The obtained signals are transformed to a digital form and averaged. The averaged digital signals are filtered to remove substantially all radio frequency interference. Absolute signals are then produced by scaling or comparing the filtered signals with a known noise level. The background noise levels are obtained by further averaging the absolute signals. A visual display unit is used to display the background noise levels as a function of frequencies. A frequency surveillance apparatus is also disclosed.

Abstract: A radar system includes a stabilization calibration arrangement wherein a module stores particular parameters for relating the radar system to a gyro which provides stabilizing data for the radar system. The storage module, the radar system and the gyro are mounted on the same mounting platform so that the particular calibration features remain with the mounting platform. With the arrangement described, the radar system is independent of the gyro and can be of a generic configuration as is advantageous for stabilization calibration purposes.

Abstract: A methodology for the measurement of the effectiveness of gap filler materials and treatments in radar cross section reduction uses an untreated calibration gap in a plate mounted at an acute angle so that specular reflection from radar illumination is diverted away from the horn antenna while monostatic reflection is returned to the antenna. A dielectric lens is used to focus the radar illumination in a narrow beam width so that edge effects of the plate are minimized, obviating the need for an anechoic facility. A spectral baseline is first determined using an untreated gap after which a relative quantitative test is performed on a treated gap. The antenna and horn may be mounted for motion along the gap to determine the electrical continuity of the gap treatment.

Abstract: A radar module includes a high-frequency signal generator comprising upper and lower parallel conductive plates, at least one dielectric rod held between the parallel conductive plates, a metal diode mount held between the parallel conductive plates, a gunn diode member mounted on a side of the diode mount, and a printed-circuit board mounted on the side of the diode mount in covering relationship to the gunn diode member and having a bias supply circuit on its surface for supplying a bias voltage to the gunn diode member. One terminal of the gunn diode member extends through a through hole defined in the printed-circuit board, is exposed in the vicinity of the surface of the diode mount, and is connected to the bias supply circuit.

Abstract: A high-frequency signal generator has upper and lower conductive plates parallel to each other, at least one dielectric rod held between the upper and lower conductive plates, a metal mount sandwiched between the upper and lower conductive plates, a oscillating element mounted on a side of the mount for generating a high-frequency signal, a printed-circuit board mounted on the side of the mount and including a bias supply circuit disposed on a surface thereof for supplying a bias voltage to the oscillating element to enable the oscillating element to generate a high-frequency signal, and a positional displacement preventing structure on at least one of the upper and lower conductive plates for preventing the mount from being positionally displaced with respect to the dielectric rod. The positional displacement preventing structure may comprise a groove defined in at least one of the upper and lower conductive plates, the mount being partly fitted in the groove.

Abstract: A multi-channel electronic communication system with equalized channels comprises a reference channel and a plurality of object channels. A white noise excitation signal is injected into each channel. Each of the channels is sampled and, for each channel, the resultant samples are windowed and the windowed samples are Fast Fourier Transformed from the time domain to the frequency domain. Power spectral density estimates are determined for each object channel from the windowed samples in that channel. Cross-spectral density estimates for each object channel with respect to the reference channel are determined from the windowed samples in that object channel and the windowed samples in the reference channel. The power spectral density estimates are divided by the cross-spectral density estimates to derive correlation ratios which are converted back to the time domain to specify a corrective equalization filter weight vector for each object channel.

Abstract: A method and apparatus for traveling wave attenuation measurement in the UHF and VHF frequency bands. The test set up comprises a ramp structure located in the quiet zone of a parallel plate set up. The RAM specimen to be tested is attached to the top ramp surface starting at the highest point of the ramp. The time domain signal is gated to reject all scattering except the contribution from the ramp surface. The inverse Fourier transform of the gated time data results in the frequency response of the ramp. The RCS from ramp with RAM material attached is normalized to that of the perfectly conducting surface to provide a relative attenuation of the surface traveling wave.

Abstract: A method for two dimensional imaging of a two or three dimensional target is disclosed. As shown, a radar transmitter transmits a beam on a beam axis originating at a position spaced from the target and a radar receiver receives return signals from the target. The stationary radar observes the precessing target whose normal to the two dimensional target plane (or whose axis through a three dimensional target) intersects the transmitted beam axis at a point, and forms a cone half angle with the beam axis. With the normal (or target axis) moving along a conical surface while precessing 2 Pi around the beam axis, signal returns from the target are processed to develop a two dimensional image of the target. The process is repeated at other cone half angles and a composite, reduced-sidelobe image generated by vectorial superposition of images at multiple cone half angles.

Abstract: Measurement of the transfer function of a space fed lens array antenna membrane is achieved by utilizing a low power test illumination antenna opposite the feed side, while a probe antenna undergoes raster scanning of a test window on an opposite target side. The probe antenna measures near field distribution on the target side and data developed enables the transfer function of the membrane to be measured.

Abstract: A digitally formed monopulse radar employing dynamic real-time calibration uring operation. The invention has a transmitter section, timing circuit, RF section, IF section, in-phase and quadrature section and a digital signal processor. A portion of the transmit signal is diverted from the transmitter section for preparation of calibration factors during the calibration period between receive signals. The calibration factors prepared by the digital signal processor are applied by the processor to antenna received signals during the receive mode and to produce the corrected sum and delta pitch, and delta yaw signals and the tracking errors .epsilon..sub.y and .epsilon..sub.p.

Abstract: A device for aligning a directional antenna of a radar distance warning device of a vehicle has an alignment spotlight connected to the directional antenna to form a rigid unit adjustably mounted on the vehicle via an adjusting board. This rigid unit is aligned by aligning the optical axis of the light cone of the alignment spotlight with the aid of a vehicle-related optical verification device, particularly a headlight adjusting device. The alignment spotlight can be removable, or the vehicle headlight can be used for alignment.

Abstract: A calibration reference target fixture is mounted on a pylon having a motorized spline extending longitudinally therethrough. The body of the fixture is teardrop shaped so as to present a low reflection cross section to a transmitting antenna. The reference target itself is a hinge-mounted plate which is driven by cam means connected to the motorized spline for selectively moving the plate between a deployed exposed position and a stored position, within the recess of the fixture body.

Abstract: Systems and methods for measuring RCS patterns of large targets in a compact target range having limited size. The present invention utilizes a compact range whose sweet spot (corresponding to the imaged area of the target) is much smaller than the target size. Inverse synthetic array radar (ISAR) images of successive sections of the target are registered to form a composite image of the whole target. The image is then Fourier transformed to generate an RCS value of the full target. This procedure is repeated for successive measurement angles, an RCS versus .theta. plot is generated corresponding to the RCS pattern of the target. The multiple images may be generated by translating the target and computing RCS plots of the target by combining the multiple images produced during translation, or generating the the multiple images by moving feeds or using multiple feeds of the ISAR system.

Abstract: In an apparatus for setting individual different electronic devices of an equipment system for measuring or detecting the properties of a selected object, a control computer is provided for cooperating with a device memory and an object memory. The device memory stores therein the individual devices of the system with their technical properties and their settable functions, while the object memory stores therein. The various object types with their properties. The control computer is configured such that, prior to performing an object measurement or detection, all object types with their properties and also the possible ways of display of these object properties are initially displayed on the screen of the control computer and the user may select therefrom the type of object to be measured or detected and the desired way(s) of displaying said properties.

Abstract: The disclosure describes a method of measuring stationary CW radar targets in the presence of sizable clutter and leakage signals, and to eliminate the clutter and leakage by taking a first measurement when the target is in a first position, and taking a second measurement when the target is translated to a second position such that the target signal pathlength changes by 1/2 wavelength from the first position, and then subtracting the first and second measurement to eliminate the unwanted clutter and leakage.

Abstract: A synthetic aperture radar (SAR) system for determining the location of stering centers on low-observability aircraft or other vehicles has an antenna that moves along a linear track relative to the stationary unit under test. When the scan is complete, the system produces an image of the aircraft showing the scattering centers. The system may then superimpose graphics representing the outline of the unit under test on the image. The operator may use the graphics to correlate the scattering centers in the image with corresponding areas of the aircraft.

Abstract: Satellite-altimetry measurements of ocean water height are calibrated by measuring an ocean water height by using satellite-altimetry at one location during a time period, measuring another ocean water height during the same time period against a known reference on a fixed offshore structure at another location near the first location, and comparing these two sets of measurements. One way of measuring ocean water height against a known reference point on a fixed offshore structure is by measuring the time it takes for pulse of energy to travel from a transmitter at that reference point to the sea surface, and back to a receiver. Another way of measuring ocean water height against a known reference point is by using water-sensitive sensors placed on the fixed offshore structure at known distances from the known reference point.

Abstract: A versatile, reconfigurable automated radar test system. The invention (200) includes a system controller (212) for providing a plurality of digital control signals. Circuitry (232, 234, 236) is provided for converting the digital control signals to static analog and digital test signals. In addition, a function generator (240) is included for generating a plurality of dynamic analog and digital test signals. An interfacing arrangement (239, 242) is included for applying the static and dynamic analog and digital test signals to a module (12) of a radar system (10) under test.

Abstract: A highly accurate remotely controlled C band signal generator which provi a microwave signal to a boresight tower for the purpose of calibrating a radar system. The C band signal generator comprises a data receiver circuit for receiving a serial digital data frame having a plurality of eight bit digital data words and for converting the words from serial to parallel. A pulse repetition generator circuit responsive to one of the eight bit digital data words provides a modulating signal having a first or second pulse repetition frequency. The modulating signal when supplied to a pin diode modulator amplitude modulates the microwave signal which is provided by a voltage tunable oscillator.

Abstract: A radar antenna arrangement (1) for a determination of the effective radar backscatter cross section .sigma..sub.eff of radar targets (2) as a function of the geometrical position of the target with reference to the radar antenna arrangement to be able to determine the effective radar backscatter cross section in a simple manner, even for a case where the radar beam no longer fully illuminates the radar target (2) to be examined and the position of the phase center (15) of the antenna (11) changes relative to the target (2), the radar antenna (11) is arranged on a rotatable antenna platform (10) outside of the rotation axis (12) of the antenna platform (10). In order to be able to scan the entire radar target (2) successively in time, the antenna platform (10) is pivotal about two axes (13, 14) that are perpendicular to the rotation axis (12). The radar target (2) to be examined is disposed on a revolving platform (3) which likewise rotates during the measuring process.

Abstract: The invention is a pylon for supporting a model above a ground plane for radar cross-section testing using a radar providing a specific frequency range and power distribution above the ground plane. In detail, the pylon comprises a column made of a low dielectric constant foam material having a base end for mounting on the ground plane, a model mounting top end and a generally circular cross-section. The column has an abrupt change in diameter at a point between the ends forming a step and dividing the column into upper and lower tapered portions with each of the portions having a specific diameter range. The step is located at a point on the column such that the power is evenly split between the upper and lower portions and the specific diameter ranges of the portions are selected to maintain a 180-degree phase change in the return signal from each of the portions reducing the RCS of the pylon.

Abstract: The invention is an apparatus for supporting a model above a ground plane for illumination by a radar signal in order to determine the RCS thereof. The apparatus includes a plurality of support towers in a spaced relationship extending vertically upward from the ground plane. An upper suspension system is provided that comprises a separate cable attached at one end to an individual tower and attachable at the opposite end to the model at a single point on the upper surface thereof so that the model can be simultaneously rotated about the yaw axis and pitch axis. A circular shaped track aligned with the direction of the radar signal is mounted below the ground plane having a center of the radius at the point that the cables of the upper suspension system attach to the model. A platform is movably mounted on the track and thus, moveable with a circular motion about the point that the cables attach to the model. The platform incorporates a drive system so that it can be positioned at any point along the track.

Abstract: The present invention is an improved direction finding (DF) processing system using digitally implemented spectral analysis. Both phase and amplitude responses are calibrated by comparing each spectrum "bin", or portion of the frequency bandwidth, to the other receiver or receivers output. A random noise source is used, with a large number of noise waveforms being measured and averaged. The average responses are then compared. The difference for each spectrum bin is stored in a passband calibration table. When the direction of origin of a signal of interest is later calculated using the difference in spectra for each bin, the value in the calibration table is first subtracted out.

Abstract: Built in test circuitry for an array transmitter. The circuitry includes a directional coupler with directivity equal to the mutual coupling between adjacent antenna elements. The direct input port of the coupler is connected to the antenna element and the direct output port of the coupler is connected to the circuitry generating the signal transmitted by the antenna element. The coupled port of the coupler feeds a detector which in turn provides an input to a control circuit. This circuit can be controlled to test, for each antenna element, the RF power driving each antenna element, the effective power radiated from each element, and the operation of the phase shifter coupled to each antenna element.

Abstract: An inflatable target support system having a minimum radar cross section, a high mechanical strength, an ultra-high rigidity and a high load bearing capacity. The system comprises a thin, inflatable, stressed-skin membrane in the shape of a right cone which is sealed at its narrow end by a extremely rigid, plug and sealed at its wide end by a chamfer shaped base so as to provide exceptional rigidity to the system.

Abstract: The object of the invention is a method and implementation means for the on-line testing of a radar information display device such as an image digital converter. The method essentially consists, firstly, in determining zones where there is no echo for a given antenna rotation then, secondly, the speeds of the displayed objects being known, in determining a second zone where there will definitely be no echo in the next rotation. In a third step, a test sequence is inserted in the second zone; at output of the function being tested, the pieces of data corresponding to the sequence, are, firstly, recorded and, secondly, blacked out for non-transmission to the rest of the chain. The recorded output sequence is then compared with the expected theoretical result, and from this comparison a piece of information on proper functioning or malfunctioning is deduced.

Abstract: A target simulates the coincident infrared and microwave signatures of a rce being tracked by a missile whose systems are undergoing test.

Abstract: A pylon for supporting a test target in an anechoic chamber during a radar cross section measurement. The pylon includes an elongated support extending upwardly from a base to a tip on which the test target is mounted. The support inclines and curves in the direction of an interrogating radar signal, and its tip is smoothly faired to the test target. The tip is formed from a resilient, radar-absorbing material, and it is bent by internal actuating means to vary the angular orientation of the test target.

Abstract: An electronic countermeasure (ECM) simulator that is particularly adaptable or use in missile fire control system vulnerability studies. A general purpose digital computer is utilized to control the simulation of true target radar skin return signals and ECM signals. These ECM signals would be representative of those produced by attacking and stand-off aircraft carrying deception and obscuration jamming.

Abstract: A CW radar comprises a substantially continuously operable transmitter (10) and receiver (16,18,20), signal operating means (12,14) for radiating the transmitter signal and for receiving at least the return signal and a reflected power canceller (RPC) circuit (26, 28 and 30) for cancelling leakage signals in a signal path from the signal operating means to the receiver. The receiver front end comprises quadrature related mixers (18,20) which supply intermediate frequency signals (I.sub.1 and Q.sub.1) to a low frequency control loop (32, 34, 36) which supplies at least a pair of control signals (I.sub.c, Q.sub.c) to a four quadrant vector modulator (28) in the RPC circuit. In order to be able to optimize the cancellation of phase as well as amplitude, the control circuit loop includes means for suynthesizing control vectors (I.sub.1 -I.sub.1, Q.sub.1 and -Q.sub.1) from the outputs of the quadrature related mixers (18,20).

Abstract: A continuously transmitting and receiving radar comprises a transmitter (10), a receiver (16), an antenna (12) and a circulator (14) for effecting communication between the transmitter and the antenna and between the antenna and the receiver. A reflected power canceller is provided for suppressing the effects of leakage between the transmitter and receiver. The reflected power canceller comprises a directional coupler (20) for supplying a part of the transmitted signal to a modulator (22) which forms a cancelling signal by adjusting the phase and amplitude of the sampled signal. The cancelling signal is applied to another directional coupler (24) which subtracts the cancelling signal from the leakage and wanted signals. A narrowband control path is connected between the output of the receiver (16) and the modulator (22). The reduction in carrier leakage and AM noise sidebands is made more effective by providing a time delay device (21) in the signal path from the coupler (20) to the modulator (22).

Abstract: An improved radar range comprising a ground plane (22), support means (28) for supporting a target (26) a selected height above the ground plane, transmitting means (24) for directing for a selected period of time an electromagnetic wave at the target, means (30, 32) for increasing the time required for the portion of the electromagnetic wave reflected off the target toward the ground plane to return to the target, and receiving means (24) for receiving for a selected period of time the portion of the electromagnetic wave that is backscattered by the target. In a particular embodiment, the means for increasing the return time includes means for recessing the support means a selected distance below the ground plane by providing a diffraction ridge (30) a selected distance from the support means toward the transmitting means with the ridge sloping down to the selected distance below the ground plane.

Abstract: A multiple-beam antenna system capable of forming a plurality of beams at one time in different directions. The antenna system has a plurality of element antennas arranged in a predetermined configuration. A signal received by each element antenna is converted to a digital signal which in turn is subjected to a Fourier transform. The Fourier-transformed receiving signal is multiplied with a Fourier-transformed weighting function. The resultant product is subjected to an inverse Fourier transform to be used for calculating an antenna radiation pattern. A holographic multiple-beam antenna is also disclosed.