Abstract: Method and system for determining position from suppressed carrier signals transmitted by satellites in which a digital representation of the satellite signals is sampled and distributed for simultaneous measurement in synchronous parallel circuits. The phases of suppressed carriers implicit in the signals are combined in a time series of measurements with phase data from a second receiver to determine position.

Abstract: A method is described modifying initially linear or planar interferometer arrays such that the arrays can be placed in conformal installations. The method commences with a conventional linear or planar array design and then using certain techniques and relationships allows for the possibility of antenna placement with materially reduced restrictions. A plurality of phase equivalent antenna locations obeying prescribed relationships are generated. These positions lie on the conformal surface on which the array is to be mounted. This permits an optimal set of antenna positions to be chosen based on operational requirements.

Abstract: An angle-of-arrival (AOA) phase unwrapping technique using a trellis search to determine the correct AOA. An antenna array having several elements arranged to establish several baselines (element spacings) between different pairs of elements receives RF signals, ranging from 1/2 .lambda. to multiples of 1/2 .lambda.. The search starts from the smallest baseline to determine the unambiguous unwrapped phase. From this least unambiguous unwrapped phase, the process then searches for the closest unwrapped phase on the second smallest baseline, eliminating the ambiguity, and improving the accuracy. As the search processes the larger baselines, the accuracy is increased, while controlling the ambiguity. As a result, the largest baseline yields the most accurate and unambiguous AOA, and results in maximum likelihood estimation of AOA.

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

Abstract: The invention provides a method for using single linear arrays for making AOA measurements only in sensor coordinates to perform emitter direction finding from an observing aircraft.

Abstract: A passive emitter location system is capable of performing emitter location autonomously from a single airborne observation platform and includes a bearing measurement system, a system for measuring doppler induced frequency shifts, and means for estimating the emitter location based on non-simultaneous measurement of the bearing and frequency using extended Kalman filters preferably initialized by a single measurement delayed initialization procedure.

Abstract: Incoming signals radiated to an array of antennas are processed within a nal surveillance system by adding signal outputs of two antennas at a common frequency. Separation of the added signal outputs according to frequency and comparison of power level measurement thereof provides signal phase difference data from which frequency and direction of the incoming signals are simultaneously determined.

Abstract: A fiber optic feed includes an optical circuit for providing at least one optical output signal modulated according to an RF source and an antenna interface for demodulating the at least one optical output signal and communicating with an antenna, wherein the optical circuit includes a coherent light source, an interferometer driven by the coherent light source for synthesizing a plurality of independently controlled planar beams, an optic modulator for frequency modulating at least one of the independently controlled planar beams according to the RF source and an optic pickup for producing the at least one optical output signal according to a superposition of the plurality of independently controlled planar beams, wherein the interferometer includes at least one beam deflector for angularly deflecting at least one of the plurality of independently controlled beams according to a beam control command.

Abstract: An embodiment of the present invention is a system for automatically pointing a directional antenna. The system comprises two GPS antennas mounted at horizontally opposed extremities of the directional antenna, the placement is such that the GPS antennas lie on a line having a normal vector approximately parallel to a boresight of the directional antenna. The outputs from the GPS antennas are downconverted to a measurement frequency and differentially phase compared for each of a plurality of radio visible GPS satellites. A measurement controller that receives the phase comparisons. A navigation computer receives measurements from the measurement controller and uses a microprocessor to calculate the GPS latitude and longitude and the attitude angles of the pair of GPS antennas. A servo points the directional antenna at a particular target communications satellite, based on the computed azimuth, elevation, latitude, and longitude, as provided by the navigation computer.

Abstract: An antenna subject to standoff sidelobe barrage jamming exhibits a null in its sidelobe structure at a selectable elevation angle for all azimuth angles of interest. The null can be set to the elevation angles corresponding to the angle of the standoff jammers. The null is generated with the aid of an interferometer associated with each column of the antenna array. The interferometer produces a pattern having a plurality of lobes. The interferometer pattern is phased and amplitude adjusted relative to the antenna pattern of its associated column line array so that subtraction of the patterns causes one or more sidelobe of the antenna pattern to be at least partially canceled. An azimuth beamformer combines the elevation patterns of a plurality of column arrays, each connected to its own interferometer, to produce a pencil beam with a sidelobe structure exhibiting a null at the particular elevation angle.

Abstract: An Angle of Arrival/Long Baseline Interferometer (AOA/LBI) passive ranging apparatus and method for emitter range determination can use any convenient airframe location for the two-antenna uncalibrated LBI baseline. This baseline has a theoretically unlimited length and does not require a specific SBI/LBI baseline ratio. Only a single initial AOA is required. Range partitions are formed along the single AOA. The emitter is assumed to lie in any of N range bins and the corresponding DOA (direction of arrival) unit vectors computed. Each of these DOA unit vectors is then used to predict the LBI phase differential and the N resolved LBI phases each drive a location estimator. The location estimator (filter) with consistent output provide the emitter range. The LBI range from these filters is used for subsequent DOA generation and ambiguity resolution.

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: An antenna is divided into a plurality of sub-arrays which are arranged parallel to each other on a turntable. At least one of the sub-arrays is laterally divided into sub-array sections. Reception signals from these sub-array sections are compared with each other to detect a phase difference therebetween. This phase difference is utilized to control the beam direction of the antenna such that the antenna can be properly oriented to the satellite at all times.

Abstract: Precise azimuth and elevation angles of arrival of a signal are determined using a rotating interferometer wheel rotatable about an axis parallel to the boresight of the interferometer. The angles of arrival are determined based on the measured phase differences of signals received by the interferometer, corresponding cone angles and the assignment of azimuth and elevation values to the group of conic lines which are nearest each other.

Abstract: Apparatus and methods of achieving accurate, unambiguous angle information with a minimum number of antenna elements. The present invention resolves the ambiguities inherent in a long baseline phase interferometer by employing a minimum number of antennas to form shorter baselines. The present invention employs roll motion (antenna rotation) to reorient interferometer baselines and a signal processor to measure the roll angle. Taking interferometer phase data with at least two orientations of the interferometer baselines permits resolution of the ambiguities. This also allows the use of long antenna baselines thereby achieving high angular accuracy with angle ambiguities resolved using only two antenna elements per spatial angle. This reduces system complexity and reduces the required clear aperture area, factors of great significance in missile systems. The invention takes phase data at two or more interferometer baseline orientations and forms a set of simultaneous equations involving the phase ambiguities.

Abstract: Method and apparatus for quickly determining the angle of arrival of a signal at a spinning interferometer based on the phase rate of changes and the cone angles between respective pulses received at the spinning interferometer.

Abstract: A distributed network that compensates for the effects of interelement coupling in a multielement antenna array is inserted between the output of an antenna array and the inputs of a receiver system. Within the distributed network are a plurality of couplers interconnected by transmission lines serving as phase shifters. The coupling factors of the various couplers and the lengths of the transmission lines are selected so as to apply voltage components of specific amplitudes and phase to the antenna ports. The values of the amplitudes and phases of these voltage components are such as to neutralize the components of the voltages at the output of the antenna array which are caused by the spatial couplings between the elements of the antenna array.

Abstract: A precision azimuth angle and .+-. elevation angle of an emitter are determined by measuring the frequency and differential phase .psi..sub.j of a received signal at each of a number of interferometer rotational positions. Each measured differential phase corresponds to a set of possible cone angles satisfying.phi..sub.j,k =cos.sup.-1 (.lambda..psi..sub.j,k /2.pi.S)where .psi..sub.j,k =.psi..sub.j +2.pi.k and .vertline..psi..sub.j,k .vertline..ltoreq.2.pi.S/.lambda.The angular distances or errors between arbitrary azimuth angles or points and each set of cone lines is determined. The point having the smallest error corresponds to the azimuth angle and .+-. elevation angle of the emitter.

Abstract: A technique for near-field tomographic imaging using a multiple-receiver correlating interferometer. A target object or scene to be imaged is located in a near-field or Fresnel region of a receiver system. The target object radiates or reflects a signal that is sensed by a plurality of antennas. The received signals are correlated using conventional correlation algorithms. An image pixel for a focal point is then computed by correcting a differential time delay between a signal emitted at the focal point and received at first and second antennas. The system is focused on the target object by correcting a phase term of the correlation algorithms. The phase term is corrected by multiplying the correlation algorithms by a phase factor. A peak correlated value is developed when the focal point is at the target object location. A series of snapshots is generated from data produced by the focussing process, as the focal point is moved through the scene.

Abstract: An apparatus and method for determining the direction of origin of a received transmission signal using a spinning antenna pair generally provides the steps and apparatus for measuring the phase difference between signals simultaneously received, coarsely approximating the direction of origin of the transmission signal, reconstructing a phase difference signal using the measured phase differences and a calculated signal based upon the coarse approximation, correcting the reconstructed phase signal based upon the first derivatives of the reconstructed signal and the calculated signal, and determining the direction of origin based upon the corrected reconstructed phase signal.

Abstract: A radiometer (100) uses the fringe pattern of an interferometer (110) to scan a scene to produce a time record from which a high-resolution radio frequency, or other radiation, distribution of the scene can be reconstructed. A matched filter (120), or other means, transforms the time record according to a function of a signature of the determinable scanning motion relative to the fringe pattern.For many applications, the modulation transfer function (123) of an included matched filter is the complex conjugate of the Fourier transform of the signature that would be produced by a constant point emitter scanned by the lobes of the interferometer fringe pattern.Two-dimensional reconstructions may be provided for by multiple scans at different orientations. Alternatively, frequency scanning or another scanning technique can provide resolution orthogonal to the fringe pattern scanning motion.

Abstract: In a point to point microwave communication service including a microwave antenna system at each point directed at the other point, the radiation pattern of the antenna system at at least one point has a substantial null in the direction of an antenna of another microwave communication service to avoid an exchange of signals with the other service, the antenna system provided at said one point includes two antenna elements having substantially equal directional radiation patterns, so oriented and spaced apart a distance that is at least several wave length of the operating frequency of the elements so that the radiation patterns of the elements overlap producing a net radiation pattern that results from interference of the patterns and the net pattern has a substantial lobe in the direction of the other point of said service and a substantial null in the direction of an antenna of the other microwave communication service.

Abstract: Techniques are disclosed for determining orbital data of space borne vehicles including earth satellites such as those of the NAVSTAR Global Positioning System. Each of a set of such satellites transmits signals which include carrier waves which may be suppressed, or only implicity present. The signals are received from the observable satellites concurrently by means of an antenna at each of at least three ground stations forming a network of baselines. The stations are arrayed such that the ratio of the maximum to the minimum baseline length is much greater than one. From the signals received at a station pair forming each baseline a time series of doubly-differenced phase measurement data is formed which is biased by an integer number of cycles of phase. The data series for different satellite and station pairs are processed together to determine the orbits of the satellites and the doubly-differenced phase biases.

Abstract: A microwave radiometer is formed of a set of frequency scanning antennas disposed parallel to each other and connected by a common microwave feeder. Signals of individual ones of the antennas are translated to different intermediate frequencies such that differences between the intermediate frequencies are proportional to baseline spacings between pairs of antennas of nested interferometers. A correlator containing parallel delay lines and a set of multiplier channels coupled to paired taps of the delay lines receives signals at the intermediate frequencies to produce a set of correlation signals. A two-dimensional Fourier transformation is applied to the correlation output signals to provide the power spectral density of microwave radiation incident upon the array of antennas.

Abstract: A radiometric imager for providing a series of registered images of a scene, each image corresponding to the radiation pattern for a unique, narrow frequency band. One embodiment includes a single frequency-dispersive linear antenna providing an output signal based on a series of conical fanbeams, with the antenna being controllably rocked about one axis and rotated about a perpendicular axis such that each fanbeam intersects each segment of the scene a plurality of times. In alternative embodiments, the imager includes a second frequency-dispersive linear antenna arranged in parallel with the first antenna to produce a fanbeam interferometer. Rocking movement of the two antennas coupled with either translation of the two antennas, rotation of the two antennas about an axis parallel with the antenna axes, or movement of the two antennas toward and away from each other, provides sufficient data to permit creation of the registered images.

Abstract: A passive detection and imaging system employs interferometric and synthetic aperture techniques. A moving platform employs a pair of sensors which receive thermal electromagnetic radiations from an area of interest. The received signals are narrow band filtered by a bank of filters covering an extended bandwidth. Signals from similar narrow bands from different sensors are correlated. The plurality of frequencies and plurality of positions relative to the area of interest due to the platform motion enable generation of an inverse Fourier transform image which is resolvable in both azimuth and range. Separate preferred embodiments operating at microwave frequencies and optical frequencies are disclosed. An achromatic optical interferometric correlation technique is also disclosed.

Abstract: An array of antenna elements is arranged along a common, rotating platform so as to form a pair of mechanically scanned interferometers exhibiting spaced, parallel receiving axes for ranging on a distance emitter. As the receiving lobes of the pair of interferometers scan across the emitter, lobe modulated signals are received having a relative time difference t.sub.21 that varies as a sinusoidal function of time due to the platform's rotation and includes a dc error value due to slight but unavoidable nonparallelism of the interferometer beams. The rate of change of t.sub.21 is derived to produce a signal t.sub.21 which drops the dc error component of t.sub.21, and which is applied as an input to a rate dependent range signal processor producing an output signal of range R as a function of the relationship ##EQU1## In this relationship d is the separation of the interferometer centers along the base line, and .phi.

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 attitude sensing system which incorporates the precision in attitude sensing of a satellite navigation system with the dynamic tracking capabilities of an inertial measurement unit. Optimally estimated attitude and system error signals are combined with the outputs of an inertial measurement unit to control the phase differences of signals received on an interferometer array from a navigation satellite. The outputs from the inertial measurement unit and the phase differences are processed in an optimal estimator filter to produce periodically updated attitude and system error signals. This permits inertial attitude sensing to benefit from the long term accuracy of attitude estimation based upon signals from the satellite navigation system.

Abstract: A method and apparatus for estimating the trajectory of a projectile using two interferometric radar antennas each producing a group of interferometric antenna lobes forming intersecting solid angles, and being directed at an elevation angle so that the projectile passes through each interferometric antenna lobe. Each radar antenna transmits a different frequency of pulsed RF power and receives pulsed RF signals reflected from the projectile whenever the projectile passes through the antenna lobes of the radar antennas. Based on the received signals of respective radar antennas, the range and time information for the projectile passing through the antenna lobes of the respective radar antennas can be obtained. From this range and time information, the three-dimensional coordinates, speed and acceleration at the points in the antenna lobes through which the projectile passes can be obtained.

Abstract: The positions of a non-cooperative emitter (illuminator) and reflector (target) relative to a receiver of electromagnetic energy, which neither directly nor indirectly controls the illuminator, is determined utilizing emissions received directly from the illuminator as well as reflected emissions from the target. A range R.sub.I between the receiver and the non-cooperative illuminator is determined by measuring the time difference between receiving the reflected signals at a pair of interferometer antennas located at the wing tips of a receiver aircraft. Calculation of the location of the target is accomplished by utilizing range R.sub.I, as well as a time differential .DELTA.t between the receipt of the reflected signals at the interferometer antennas and the receipt of a corresponding direct signals at a radar antenna located at the aircraft. In the event there is clutter in the reflected signal which hinders the determination of the time differential .DELTA.

Abstract: A method and apparatus for passive ranging from a moving platform to a stationary, non-cooperative emitter utilizes a Long Baseline Interferometer and a Short Baseline Interferometer, the former to provide a very precise, but highly ambiguous, measurement of change in phase occurring between two points along the moving platform's path, and the latter to provide a measurement of the emitter's angular position relative to the platform's path at the two points and to resolve ambiguities in the phase change measurements of the former, resulting in a system with enhanced accuracy over prior art devices which may be used against signals that are phase-coded, frequency-coded or frequency-hopped. An error model and a criterion for optimization of the system in terms of measurement error, interferometer length and orientation, and vibration amplitude are presented.

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: Apparatus for applying a test static-electric discharge from a test tip to equipment under test in two modes, which apparatus includes a capacitor, a power supply, and a normally closed relay for connecting the high side of the capacitor to the tip. Means are provided for actuating the relay to open and close, and means are provided for actuating the power supply to charge the capacitor. In an air-discharge mode, the power supply is actuated for charging the capacitor while the relay is closed and thus not energized. For direct-injection mode operation, the apparatus includes a timing circuit interconnected so that the relay is opened a finite delay time before power supply is actuated to charge the capacitor, the relay remaining open until the capacitor is charged, and thereafter the relay automatically closes to permit discharge of the capacitor.

Abstract: A direction-finding interferometer (100) includes a novel autocalibration subsystem using bi-directional transmissions at a common frequency. The interferometer determines direction using a primary phase comparator (15) to assess the phase differences in signals transmitted by signal channels (13) from multiple antennas (11). The signal channels may include RF amplifiers (17), mixers (19) coupled to a local oscillator (23), IF amplifiers (21), and transmission lines.The autocalibration subsystem employs a frequency synthesizer (25) as a calibration signal source. The calibration signal path is directed between reversing switches (40) and couplers (33) in alternating directions via transmission lines (57 and 59). In either direction, the calibration is split so that part of the signals are coupled into the signal channels, and the remaining part is directed to a secondary phase comparator (131). The outputs of the primary and secondary comparators provide the data necessary for autocalibration.

Abstract: An interferometer type DF system uses an array of five antennas (A,B,C,D,E) arranged at the apices of a regular pentagon to define five wide apertures along the sides of the pentagon and a further five apertures along the diagonals. The phases of the signals received by each antenna, are measured modulo 2.pi. and processed to give a unique bearing of the radio source to the accuracy of the widest aperture defined by the array. One method of processing the phases is to calculate from them the Fourier coefficients of the Fourier series representing the spatial phase distribution. By comparing the difference between each calculated coefficient and a corresponding order coefficient of a set of imaginary antenna phases expressed as integral multiples of 2.pi., the complete 2.pi. phase differences between the measured phases modulo 2.pi. can be found.

Abstract: A two-dimensional, long baseline (D) direction finding interferometer (12) is provided for obtaining unambiguous spatial position of an object. The interferometer comprises four antenna receiving means, (A1, A2, A3, A4) which are arranged in a two-dimensional, planar fashion. Three of the antenna means (A1, A2, A3) are positioned on two orthogonal axes (D, D.sub.2). The remaining antenna (A4) means is positioned on a third axis (D.sup.1) which is arranged asymmetrically and nonorthogonally to the orthogonal axes, whereby the unambiguous spatial position of the object is determined.

Abstract: Incoming radio frequency signals from one or more remote transmitters, that may be changing or "hopping" in frequency, are received at two closely spaced antennas. A pair of Chirp-Z transform processors are respectively coupled to said antennas. The transform processors are operated in synchronism and produce a pair of sampled comb filter output responses, each of which comprises a multiple of frequency "bins" distributed over a given spectrum. The bins are read out of the Chirp-Z processors in a synchronous sequential order, and each bin is represented by a pair of signals in phase quadrature. The phase quadrature signals of corresponding bins are multiplied in a predetermined manner and the products thereof are selectively added and subtracted to provide a predetermined function (tan .PHI.) of the phase difference (.PHI.) between the signals incident on the pair of antennas. This predetermined function is coupled to a processor that calculates a trigonometric function (sin.sup.