Abstract: A radio direction finder based on the simulated Doppler frequency shift principle is disclosed that is applicable to FSK encoded pulsed transmissions. Typical applications include tracking of stolen vehicles or shipped package tracking. During FSK decoding, all antenna elements of the antenna array are turned on in a non-rotating mode thus eliminating error due to the simulated antenna rotation modulation while providing enhanced gain for the FSK decoder circuit. After decoding a suitable FSK signal, a virtual antenna rotation is enabled, and the bearing is measured during the time interval when the transmitter is only broadcasting a carrier wave.

Abstract: In a direction finder, a frequency distribution of the directions in which radio sources are located is obtained in a manner that an antenna platform is rotated while setting an instantaneous field of view invariable or varying the same, whereby the above phenomenon is suppressed.

Abstract: This invention relates to a wide aperture radio frequency data acquisition system which collects coherent samples from multiple points in a defined plane at the surface of the ground. The information collected can be processed with suitable algorithms to extract the bearing, frequency, and power spectra of the arriving radio frequency wavefront.This system consists of an antenna system; a multi-channel receiver system incorporating mixers, filters, amplifiers, analog to digital converters, digital down converters; a digital signal processor; and a computer. The electrically short, active antennas with frequency independent response are connected to the multiple channel receiving system, one channel per antenna receiving the signal. The receiver uses two frequency conversion oscillators for coarse but accurate frequency synthesis to convert the received signal's frequency. Then, the signal is converted to a digital signal.

Abstract: A method of detection and tracking of targets using multiple angle-only sensors is disclosed. The method is computationally efficient and is capable of detecting and tracking multiple targets in true three dimensional space. The method comprises distributing a set of modules in space and associating those modules with bearing lines from each sensor to each target. Through repetitive iterative associations between modules and bearing lines, the modules converge on the targets present.

Abstract: Method and apparatus for determining the attitude or angular orientation of a moving vehicle or other moving body, using either two spaced apart antennas or a single antenna attached to or connected with the vehicle. Where two antennas are used, the spatial locations of each antenna are determined at a first selected time, and the spatial location of one antenna is determined at a second selected time. These three spatial locations determine a plane whose normal vector allows determination of the vehicle attitude at a time determined by the first and/or second selected times. Four or more spatial locations can also be used to determine a plane that indicates vehicle attitude. Where one antenna is used, for example, in a vehicle turn, the antenna spatial locations at three distinct selected times determine a plane that allows determination of the vehicle attitude at a time determined to the first, second and/or third selected times.

Abstract: An electrical surveillance measures system for measuring direction of arrival (DOA), i.e., both azimuth and elevation, of a pulsed or continuous wave radar signal from a moving emitter. Either carrier frequency or pulse repetition interval (PARI) Doppler shift are used whereby the ratio of the Doppler shift is measured by a moving observer. The DOA is measured as a unit vector having basis vectors formed from a linearly independent set of observer's velocity vectors. The DOA unit vector has a linear part where the coefficients of the basis vectors are derived directly from the ratios of frequency or PARI measurements taken in three contiguous dwells. The DOA unit vector has a nonlinear part formed from the requirement that the DOA vector have unit magnitude. The unit vector is resolved in the system coordinates in which emitter azimuth and elevation are defined to allow computation of the latter two values.

Abstract: This disclosure relates to multi-element antenna clusters or arrays for the reception and transmission of radio waves for direction-finding, navigation aid and emitter and/or receiver location purposes. In particular, it relates to arrangements of multiple antennas whereby the direction of propagation (arrival or departure) of a wavefront is determined from a combination of the amplitudes of phasor (or total individual antenna output) differences between pairs of antennas, said arrangements being along certain geometrical patterns, such as a circle, an ellipse, a polygon, an open straight line, etc., with at least one longest dimension measuring more than one wavelength of the incident or departing wave. Although described in terms of electromagnetic waves and hence antennas as receiving sensors or radiators, this invention in reality applies to any other form of propagating waveborne energy, such as acoustic, ultrasonic, seismic, etc.

Abstract: Method which involves determining the position of a number of measured objects by determining a number of directions to the measured objects from at least two measuring stations, of which at least one is mobile, the method being used to decide which of the points of intersection between the directions correspond to measured objects and which ones do not correspond to measured objects. Changes in the mutual movements between the measuring stations and the points of intersection are in this case determined by comparison between the paths in which the points of intersection and the measuring stations are moving. The points of intersection whose movement is not affected by changes in the movement of other points of intersection, or by changes in the movement of at least one measuring station, correspond to positions of measured objects.

Abstract: A precision direction finding system for making precision angle of arrival estimates for a signal received through two antenna elements separated in space. Phase interferometry is used to determine a precise angle of arrival, with multiple ambiguities due to the periodic nature of the phase difference related to geometric angle. The interferometric ambiguities are resolved using the time difference of arrival (TDOA) of the signal at the two antenna elements. TDOA is measured using leading edge envelope detection for simple pulsed signals, and predetection correlation for phase and frequency modulated signals.

Abstract: The radio frequency (RF) security system includes a central control unit and a plurality of portable transmitters (up to 128 transmitters) which are in radio frequency communication with the central control unit. This communication is one-way from the portable transmitters to the central control unit. The central control unit and the portable transmitters both include microprocessors and associated memory. Each portable transmitter is assigned a unique unit binary code. In order to detect destruction of the transmitter unit, a powerline is imbedded in an elongated band which is placed on the wrist of a child or attached to an inanimate object. When the band is severed, the powerline is severed and the microprocessor in the portable transmitter is shut down. During normal operation (without the band being severed), the portable transmitter has an RF transmitting circuit which is fed the unique unit code and which frequency modulates (FM) the RF carrier signal with the unit code.

Abstract: A method and apparatus determines the location of a signal transmitter located at an unknown location by using externally-induced intermodulation distortion emitted from the signal transmitter. A transmitter locator emits an interrogation signal having a frequency that is offset from the frequency of the signal emanating from the signal transmitter. The interrogation signal and the carrier signal of the signal transmitter are "mixed" within the signal transmitter to form an intermodulation product signal. The intermodulation product signal having a different frequency is then radiated from the unknown signal transmitter. A receiver tuned to the frequency of the intermodulation signal detects the returned signal and a processor determines the range and direction from the transmitter locator to the location of the signal transmitter.

Abstract: Method and apparatus for passive emitter location which overcomes the time to range and other restrictive limitations of passive tracking systems by combining pulse frequency, time of arrival and bearing or angle of arrival measurements to obtain a range measurement at each parameter update. No specific observer motion is required and relatively few restrictions on emitter motion are present in order to obtain an accurate determination.

Abstract: A directional antenna configuration for use in an article tracking system includes two shorted loops, one on each side of a portal and in each case circumscribing the portal. The antenna configuration also includes a respective pair of passage antennas provided on each side of the portal. The passage antennas are all arranged in planes parallel to the path of travel through the doorway. The respective loops confine the effective detection areas of each pair of passage antennas to the respective side of the portal. The antenna configuration permits reliable detection of direction of movement through the portal.

Abstract: An apparatus for determining a spatial angular reference to an emitter of RF signals, such as direction of arrival or angle of arrival, from phase measurements made between two antennas is described. The apparatus uses at least a pair of dual polarized antennas having non-parallel boresights. Like polarized outputs from the antennas produce phase information which is stored and then summed to remove bias error in favor of the sin (AOA) component, while the phase information from the like polarized antennas is also differenced producing a signal indicative of the bias error. It is shown that the bias error can be uniquely related to emitter angle and azimuth. The latter information is obtained without the need for making emitter frequency measurements.

Abstract: In an air traffic advisory system for determining the bearing of an intruder aircraft relative to a protected aircraft, the preferred apparatus determines a corrected bearing to compensate for bearing errors caused by intruder signal reflections. More particularly, the preferred apparatus uses a hybrid combiner to produce a sum, delta one and delta two signals, and determines the phase relationship between the sum signal and each of the delta signals, the two phase relationships being subject to at least partially offsetting errors due to intruder signal reflections. The apparatus determines an uncorrected intruder bearing from each phase relationship and then averages the uncorrected bearings to produce a corrected intruder bearing.

Abstract: A plurality of monitors are distributed throughout a surveillance area chosen in the wild habitat of animals by a sportsman. Each monitor transmits at least one infrared signal to the surveillance area. An animal intersected the beam reflects incident radiation on a detector situated in the same housing as the transmitter. When the signal is detected, an RF transmitter is energized for detection at a remote site by an RF receiver. The RF receiver includes a clock for establishing the date and time of the transmitted signal. In the preferred embodiment, each monitor is provided with three (3) infrared transmitters, each with an associated receiver. The transmitters are driven by encoded signals that uniquely identify each transmitter of the monitor as well as the transmitters of all other monitors that may be in use thereby to enable detected directional movement in the surveillance area. The receiver includes a decoder for establishing the identity of the received RF signal.

Abstract: A method for determining the direction to a signal source by cooperation between a first device which determines the direction to the signal source with a low angular accuracy and a second device which determines the direction to the signal source with a high angular accuracy. In a first step, the direction to the signal source is determined within a certain angular range and, through analysis of the signal transmitted from the signal source, the category of the signal source is determined. In a subsequent second step, an angular search for a signal source of said category is performed within the angular range, in which the search is interrupted in the direction in which a signal of the category is detected. In a subsequent third step, the detected signals are correlated with respect to time. When correlation is present, the direction to the signal source is determined by determination of the direction in which the signal source is detected.

Abstract: This invention relates to a system to alert an aircraft pilot of the presence and general location of other aircraft that might constitute a collision threat to the pilot's aircraft. A first and second antenna on the upper paid lower surfaces of the aircraft each operate in first and second modes characterized by respective first and second directivity conditions. The first and second antennas directly receive pulse signals from a source in order to determine the relative time of arrivals and thus the relative altitude of the source to the aircraft. Analysis means compares amplitudes of responses in the first and second modes to provide an angle indicating signal without having to generate radio signals other than those already being generated by equipment in the other aircraft in response to ground ATC interrogation.

Abstract: A ground unit capable of being carried on the back of a member of the armed orces is used in conjunction with a marker beacon. The ground unit detects and identifies the signals from the marker beacon and is also capable of indicating the direction in which the marker beacon is located. For identification purposes, a received signal at the ground unit from the beacon is checked with a known identification code signal inserted in the ground unit by the user. Upon detection of the signal the user can determine the direction to the marker beacon by scanning with a hand-held antenna system. Visual and audio information is provided to the user.

Abstract: A solution to the AOA problem is provided, receiving the data via a plurality of antennas, which uses a switching network to couple the antennas to a single receiver and a single analog-to-digital converter to digitize the incoming signal. It is possible to solve the problem where there might be multiple signals present. In the receiver, the incident radiation is mixed with a local oscillator signal and down converted to an intermediate frequency (IF). This IF signal is discretely sampled in the analog-to-digital converter, and further processing is done using digital techniques. The incoming signal has to be phase compared to obtain the angle of arrival. Different delay times are used to receive the digital data from the different antennas at the same sampling times, with the data aligned according to the time axis. The frequency of the incoming signals can then be detected by performing a Fast Fourier Transform (FFT) on the data from one antenna with respect to time.

Abstract: A system for reducing co-channel interference includes a power spectrum analyzer which provides a spectral signal representative of an intermediate frequency signal from the receiver of a direction finding system. The system further includes threshold/window logic that, responsive to the comparison of threshold levels and spectral windows to the interfering signals, will provide stop and continue signals to an integrator. The integrator receives signals from the direction finding system and stops and starts integration of the output signal responsive to the threshold logic. In so doing, co-channel interference is substantially reduced.

Abstract: A device and method for reconstructing a vector wave and its source direction by measuring the amplitudes of the vector wave in directions chosen according to a necessary and sufficient condition that ensures that the measured amplitudes contain enough information to provide a unique set of relative phases among the sinusoidally time-varying components of the vector wave. Together with the amplitudes, these relative phases are processed by a microprocessor to yield the polarization characteristics of the vector wave and the direction of its source.

Abstract: A mobile direction finder for tracking a remote transmitter computes the transmitter direction relative to the direction finder and time-averages with reference to a datum derived from a predetermined orientation independent of the direction finder orientation.

Abstract: The disclosed system measures the phase relationship of first and second K signals received at a pair of receiving antennas. The antennas are connected to respective first and second converting circuits which convert the received signals into first and second CW signals. Each CW signal is subjected to chirp-Z processing so as to convert the first and second CW signals into first and second chirp-Z transforms, which are narrow pulses. Then, the phase relationship of the first and second narrow pulses is detected, so as to thereby detect the phase relationship of the first and second received BPSK signals. That phase information can be used, for example, to calculate the angle-of-arrival (AOA) of the received BPSK signals. Advantageously, each converting circuit includes a series connection of a frequency-doubling circuit, a bandpass filter, and a circuit for dividing frequency by two, in that order.

Abstract: A detector for use on board an aircraft traveling along a path of movement to detect a power line comprises an antenna for sensing the electric field associated with the power line and producing an electric field signal, and a signal processor for receiving the electric field signal and generating a time-to-impact signal representative of the time for the aircraft to reach the power line if it continues on its path of movement. Sensors are used to determine the direction of the power line.

Abstract: This invention relates to a system to alert an aircraft pilot of presence and general location of other aircraft that might constitute a collision threat to the pilot's aircraft. An antenna means operates in first and second modes characterized by respective first and second directivity conditions resulting in first and second gains for signals from a certain direction. Analysis means compares the amplitues of the first and second responses to produce an angle-indicating signal locating a potential collision threat without having to generate radio signals other than those already being generated by equipment in other aircraft in response to ground ATC interrogation.

Abstract: A microwave signal detector system provides a visual indication of the relative bearing of a remote source of microwave energy. An antenna for receiving said microwave energy includes a plurality of microwave-sensitive elements arranged in a planar circular array for receiving pulses from all azimuth directions. Each microwave sensing element is adapted to monitor energy received in a predetermined angular sectors and includes a horn element and a microwave energy responsive diode disposed within said horn element. The diode is connected as part of a voltage divider to develop a noise signal corresponding to the microwave energy received at each sector resulting from vibrations in the diode which occur at an audio frequency. The resultant developed noise signal is digitized and compared to a predetermined threshold to provide an output control signal when the developed signal exceeds the value of the threshold. The output signal drives an LED indicator.

Abstract: An adaptive antenna array system steers a plurality of antennas to direct e null toward an undesired source of interference to reduce noise and enhance detection of desired signals. A null indication processing system adjusts the phase and amplitude of the antenna branches to steer the null and provide a null angle indication and display. Digital controller and memory circuits provide automatic operation.

Abstract: The present invention pertains to a radiowave relay station in which image information or the like is transmitted by a helicopter from a first station to a second station. A direction finding device is provided which detects the direction of a transmitting source, i.e., a first station. The direction finding device calculates the vertical directional angle .phi. representing the direction of an incoming radiowave which is transmitted from the first station. This direction finding device allows the helicopter performing a relay function to fly rapidly to a contact point with the first station, i.e., in a vicinity of the first station. The direction finding device may also provide information to control an antenna driving portion for adjusting a receiving antenna located on the helicopter.

Abstract: A method and a system are disclosed for measuring the baseline vector b between a pair of survey marks on the ground by radio interferometry using radio signals broadcast from the earth orbiting satellites of the NAVSTAR Global Positioning System (GPS), the radio signals broadcast by the satellites being double-sideband modulated with their carriers suppressed. The signals received by one antenna during a predetermined time span are separated into upper and lower sideband components. These separate components are filtered, converted to digital form, and then multiplied together. Differences in Doppler shift are utilized to distinguish the carriers of different satellites. Thus, the powers and carrier phases of the signals from a plurality of satellites are measured simultaneously and numerical data representing the measurement results are obtained at each survey mark.

Abstract: A wake plotter apparatus capable of displaying the bearings of a vessel and a target point in which the vessel is intended to be returned is disclosed which includes a compass sensor, a speed sensor, a displaying device and a central processing unit.

Abstract: An improved vehicle or other object-tracking and location system, preferably, though not essentially, of national scope, wherein transponder or transceiver-equipped stolen or missing vehicles or other objects may be located and/or tracked, as by appropriately-equipped police direction-finding tracking vehicles, through homing-in on periodic transponder reply radio transmissions automatically activated by command activation signals broadcast on the same carrier frequency as the transponder reply signals and with encoded vehicle identification information that causes the intended vehicle transponder so to reply, and with provision for modifying the command signals to require an increased rate of periodic transponder reply signal transmission to assist homing-in on the selected vehicle.

Abstract: A discrete fourier transform direction finding apparatus for performing a direction finding function on signals received through two antennae separated by a known distance. The outputs of the respective antennae are connected to first and second receiver channels which convert the received signals down to baseband and provide orthogonal I and Q channel outputs. A common local oscillator is used to maintain phase coherency between the channels and AGC signals are provided to maintain identical delays in the receiver RF paths. The processed signals from each receiver channel are than fed into a respective charge coupled device Chirp-Z transform (discrete fourier transform) circuit to produce real and imaginary components of the received signals. These signals are then converted to digital form and are used by subsequent circuitry to determine the angle of arrival of the received signal.

Abstract: A signal processor for radar systems having phased array antenna structures. The processor determines the angle of arrival of the signal from a discrete energy source. The separate elements or output ports of the antenna structure are sampled to form a matrix of signal values. These values are converted into polynomial expressions consistent with one of the spectral estimating methods of maximum entropy, maximum likelihood, and thermal noise. The roots of the polynomial expressions are found and compared to the distance of the unit circle in a pole-zero diagram. Roots sufficiently close to the unit circle are selected as representative of the source signal peaks and the angular directions to such sources are determined by the corresponding angular location of the selected roots in the pole-zero diagram.

Abstract: A codeless digital method and apparatus for obtaining measured phase from a plurality of L2 signal transmissions. An intermediate frequency signal is derived by mixing the L2 transmissions with a local oscillator. That signal is hardlimited and employed to terminate the count of a divide-by-32 counter that is clocked by the local oscillator signal and initiated by a signal in synchronization therewith whose frequency is a fraction of the local oscillator. The state of the counter is applied to a four bit latch. The state of the latch, which effectively discards the most significant bit of the count, provides the measured phase of the L2 transmissions from which position can be obtained by reference to the satellite phase and delta range values derived therefrom.

Abstract: In, for example, a passive direction-finding radio receiver employing a multi-beam antenna which has e.g. ninety-six feeds which form a corresponding number of overlapping reception beams, the output signal amplitudes of the various feeds can be compared with a reference to yield a sequence of binary digits, e.g. as shown in FIG. 2. The position of a radio source is given by the position in the sequence of the center of the largest group of "1"s. In order to quickly determine this position the sequence is subjected repeatedly to a processing operation in which each "1" which does not have "1"s as its two immediate neighbors is changed to a "0", thereby repeatedly stripping the two end "1"s off each group of "1"s until none remain. The required position is that of the single "1" or pair of "1"s present immediately before all have become "0"s.

Abstract: An image sorting system such as an airborne defense system for receiving and classifying enemy radar signals according to frequency, azimuth angle of arrival, etc. It employs a RAM that is addressed by the frequency and azimuth values of each received signal. If the addressed storage location in the RAM is empty, a number is assigned and stored there to represent the radar that is producing the received signals. The RAM represents a map of the aircraft's environment. Hash addressing, chaining of overlapping radar signals, pipelining to facilitate the blocking of superfluous pulse Doppler signals, etc. enable rapid reliable sorting and identification of hundreds of radar or other signals in the area.

Abstract: A navigation method for independently determining direction and for determining course for aircraft with low quality gyros and an external, calibrated magnetic course sensor. The method, which functions in the event of failure of the magnetic course sensor, is based upon the concept of determining, from the magnetic course last determined prior to failure as corrected by the local declination, and the true course as determined by the quotient of the two gyro horizontal axes distorted by the gyro drift, a "synthetic magnetic course" for course support.

Abstract: An adcock DF-on-the-fly type direction finding system employing a beam forming dispersive delay line (BFDDL). A square array of four elements A1, B1, C1, and D1 with A1, C1 and B1, D1 being the diagonal pairs is used to input signals to combiner, shifter and summer elements to produce signals representing S.sub..phi. =A1+B1+C1+D1 and S=(B1-D1)+[(A1-C1) shifted -90.degree.]. S.sub..phi. and S are input to the BFDDL which produces output signals sampled from the output spatial interference pattern of the BFDDL at 90.degree. intervals. The output signals from the BFDDL are used to calculate the arrival of the signal of interest as being substantially equal to the phase shift between S.sub..phi. and S.

Abstract: In a direction finder operating according to the Watson-Watt principle and having two separate receivers (3, 4) of the same type and of simple construction for the signals of the two crossed directional antenna systems (A, B, C, D), the vectorial simulation signals VN in a transmission line for intermediate frequency antenna signals are compared to vectorial rectified signals VV in order to compensate the phase shift caused in both receivers by means of an adjustable phase shifter (21). The vectorial signals VV are selectively derived from the antenna signals as sum signals or difference signals. In one embodiment, a reconstructed phase signal is obtained by reverse pulse control in a direction finding ellipse generator (24, 25) having two outputs on the basis of the difference between the vectorial rectified signal VV and the rectified vectorial simulation signal VN.

Abstract: A data analysis system accepts time related data samples which are develo from sets of common wavefronts incident upon a plurality of sensors. The data samples are converted from analog-to-digital form and the Fourier transforms relative to the frequency components are generated. The frequency components of the Fourier transforms are in turn cross-correlated for developing matrices of all possible correlations for each frequency component and then the matrices are integrated over a determinable time period. The resultant integrated matrices are compared with signals representative of an incident plane wave power as a function of its angles of arrival at a sensor array and of its frequency, producing output signals of relative strength indicative of the direction of the origin of the data samples.

Abstract: A surveillance system for simultaneously identifying the directions and frequencies of a plurality of electromagnetic-radiation sources includes an irregular array (10) of antenna elements and employs a two-dimensional compressive receiver (14) that receives at its input ports (18) the individual element signals. Each output of the two-dimensional compressive receiver (14) is modulated in an associated modulator (20) by one signal of a composite ensemble of signals. The composite ensemble is the sum of a plurality of individual ensembles, each of which is an ensemble of signals of a frequency uniquely associated with that individual ensemble and individually modulated to favor a direction associated with that individual ensemble. The results are added together in summation circuit 22 and applied to a Bragg cell (24), which segregates the results of modulation by the individual ensembles.

Abstract: The present invention relates to a method and a receiver for radionavigation, said receiver comprising a single filter mounted downstream of a mixer and adapted to allow the passage of the composite signal formed by the superposition of the signals of lower frequency at the output of the mixer, a sampler intended to sample the composite signal filtered at a predtermined frequency (f.sub.e), a unit intended to produce by a frequency analysis operation a series of signals including the same frequency components as the composite signal and means adapted to establish the phases and, if appropriate, the amplitude of the signals produced in the receiver by correlating these signals with the samples obtained from the sampler.

Abstract: The invention of this disclosure comprises a system that simultaneously determines the frequency and direction of arrival of incoming signals. The apparatus of this invention comprises a layered half space dispersive delay line which is utilized as a beam forming element in a device that performs a two-dimensional Fourier transform on a function which is both time and space dependent.A pulse appears at the end of the delay line at a time which corresponds to the frequency of the incoming signal and the position of the pulse along the edge of the delay line is related to the direction of arrival of the incoming signals.

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 bearing indicating R.F. system comprising two spaced, broad-beam antennas supplying signals via power dividers to amplitude comparison means and phase comparison means, both operating without down-conversion to I.F. The main lobes of the radiation patterns of the antennas are inclined towards one another so that for non-normal incidence there is a difference between the amplitudes of signals received by the antennas. The amplitude comparison means comprises detector diodes, logarithmic amplifiers, and a first subtractor, the magnitude of the output signal (sensed with a threshold detector indicating which side of normal the radiation is incident. The phase comparison means comprises a hybrid ring having "sum" and "difference" output ports connected to an instantaneous frequency measuring apparatus and a detector diode, and further comprising logarithmic amplifiers and a second subtractor, the outputs of detector diodes in IFM being summed to provide a signal output connected to one amplifier.

Abstract: The angle of arrival (.theta.) of an RF signal is determined using only two widely spaced antennas (A, B). A coarse/fine measurement system (40) is disclosed wherein the actual time delay between zero-crossings responsive to the same RF carrier cycle within the pulse envelope arriving at each antenna is determined. There is no need for additional antenna pairs with different baselines to otherwise resolve ambiguity.

Abstract: A radio direction finding system comprises a receiving portion for receiving a radio signal and a direction determining portion coupled to the receiving portion for developing a direction signal corresponding to the direction of arrival of a received radio signal. A memory is also provided for storing direction data corresponding to the direction of arrival of at least one received radio signal, and a control circuit is coupled intermediate the direction determining portion and the memory for producing direction data corresponding to the direction signal for storage by said memory. In accordance with a further aspect of the invention, an indicator is provided for actuation by the control circuit to produce an observable indication of the direction of arrival of a received radio signal, and the direction finding system further includes an EPIRB detector portion for producing an EPIRB reception signal in response to reception of an EPIRB signal.

Abstract: A monolithic microwave integrated circuit including an integral array antenna. The system includes radiating elements, feed network, phasing network, active and/or passive semiconductor devices, digital logic interface circuits and a microcomputer controller simultaneously incorporated on a single semi-insulating GaAs substrate by means of a controlled fabrication process sequence.The resulting integrated circuit structure built upon a semi-insulating GaAs substrate provides a unique monolithic structure capable not only of phase-shifting, amplifying or otherwise controlling and conducting r.f. electrical signals but also capable of directly radiating/receiving r.f. electromagnetic emanations propagated to/from the integral antenna elements of the monolithic structure.