Abstract: When an IFF system interrogates a target aircraft and receives IFF reply signals, monopulse processing of the reply signals can provide more accurate determination of target azimuth. However, when reply signals have amplitudes close to noise or jamming levels, azimuth processing by non-monopulse techniques such as beamsplitting or center of gravity analysis can provide better accuracy than monopulse azimuth processing. Methods are described to enable adaptive selection of the type of azimuth processing to be employed. Such selection is based on active comparison of received signal magnitudes against monopulse sum and difference signal threshold values and a noise threshold value. Monopulse azimuth processing can thus be used at all times, except when non-monopulse azimuth processing is chosen by such adaptive selection.

Abstract: A dipole array antenna is configured for improved cellular operation by avoidance of metallic contacts which can lead to generation of intermodulation products (IMP). Isolated rectangular dipole radiators 12-17 are electromagnetically excited by perpendicularly aligned non-contacting exciter resonators 40-45. The rectangular exciter resonators 40-45 are integrally formed with microstrip signal distribution feed 18 supported above a ground plane 22. A non-contact RF grounded termination for the outer conductor of coaxial input line 52 uses a quarter-wave microstrip line section 56 to provide a low impedance RF path to ground to avoid IMP. An RF-isolated DC grounding circuit for surge protection includes a parallel combination of quarter-wave line sections 62 and 66. Line section 66 provides an RF open circuit path to a DC grounding post 67. Line section 62 provides a parallel non-contact low impedance RF path to ground, avoiding IMP from flow of an RF current through pressure contact points at post 67.

Abstract: In a cellular type communication system a sector antenna 12 provides coverage of a sector with a relatively low receive gain. A multi-beam antenna 20 covers the same sector with a plurality of narrower beams 21', 22', 23' and 24' providing higher gain. A multi-beam antenna system 10 provides higher gain operation by selecting the one of the narrower beams 21', 22', 23' or 24' currently providing best reception of a signal transmitted by a user and coupling that selected beam to a system receiver 18. Beam selection is accomplished by sequentially coupling each narrow beam to a microprocessor based control unit 40 and storing samples of user signals as received in each narrow beam on a continuing repetitive basis. The stored samples are then analyzed in order to select the beam currently providing best reception.

Abstract: Multi-beam antennas with relatively large effective apertures for high antenna gain are provided for tower or pole mounting for cellular and other uses. Low wind resistance is achieved by use of thin cylindrical radiating units and thin cylindrical tuned reflector units. Each radiating unit includes separately excited upper and lower radiators, each including a microstrip pattern of a phase reversed series of half-wave transmission line sections on a substrate enclosed in a fiberglass tube radome. Each tuned reflector unit includes a resonant stack of electrically isolated metal rods enclosed in a fiberglass radome. In one embodiment, four cylindrical radiating units, each including upper and lower radiators, are laterally spaced in front of upper and lower reflector configurations, each including seven laterally spaced tuned reflector units.

Abstract: Simplified, high reliability slot array antennas are usable in cellular communication systems. In a flat panel form, an antenna includes a slot array with simplified feed enclosed within a back panel and a front radome structure. Use of a simplified feed, consisting of a vertical aluminum rod dielectrically spaced from an aluminum sheet including a vertical array of horizontally aligned slot openings, is made possible by horizontal slot offsets. With a linear feed rod, signal coupling to each slot in series is determined by the horizontal location of each slot relative to the feed rod. With a capacitive input coupling, there are no electrical contacts or connections in the internal feed path which may cause intermodulation effects. With a grounded aluminum array sheet and case construction, and capacitively-coupled feed, the antenna is resistant to lightning strikes.

Abstract: A system and technique for detecting a recurring signal, for example, a synchronization pulse contained in an information signal stream modulated on a carrier signal, wherein the recurring signal has a known duration (.tau.) and a known period (T). The signal carrier is demodulated such that the recurring signal exhibits a certain characteristic amplitude variation over its duration .tau., and the demodulated signal carrier is sampled at intervals less than .tau. thereby obtaining signal samples exhibiting the amplitude variation of the recurring signal. The signal samples are applied to an input of a coincidence network including at least one delay circuit which provides a delay corresponding to the period T of the recurring signal to a passing signal sample, and input and output terminals of each delay circuit are coupled to different inputs of an associated coincidence gate circuit. Each coincidence gate circuit produces an output whenever its input signal samples coincide with one another.

Abstract: Antenna systems particularly suited for reception of GPS satellite signals include a vertical stack of element arrays. Each array, which may comprise four dipoles positioned around a central axis, receives signals phased to produce a circularly polarized 360 degree progressive phase radiation pattern around the axis. By rotating in azimuth the radiation patterns of certain of the element arrays and controlling the amplitude of signals applied to different arrays in the stack of arrays, a circularly polarized radiation pattern can be provided encompassing the entire upper hemisphere above the horizon, with a sharp pattern cutoff at or slightly below the horizon. A seven array stack of individual arrays each including four angled dipoles, with a distribution network for providing signals of desired relative phase and relative amplitude to each of the 28 included dipoles, is described.

Abstract: A beam sharpened antenna pattern is achieved by intercoupling signals from individual radiating elements of an array to produce a sum mode signal and a ring mode signal. The ring mode signal represents a forward-directed antenna pattern having a zero to 360 degree progressive phase characteristic around a pattern axis. Beam sharpening results from processing the sum and ring mode signals to provide a pattern having 360 degree beam sharpening, which represents portions of the sum mode pattern of amplitude greater than the amplitudes of selected portions of the ring mode signal. The ring mode signal may be provided on a predetermined basis after selected attenuation or amplification in order to provide a beam sharpened antenna pattern having a modified characteristic. In some applications, received signals are processed on a simultaneous sum mode and ring mode basis, while during transmission pulsed sum mode and ring mode antenna patterns are activated on a sequential, timed basis.

Abstract: A local R.F. ground plane for high frequency active device. The R.F. grounded terminal of each active device is connected directly to its local R.F. ground plane. In the case of a transistor, there are common emitter, common base, or common collector circuits. The common electrode or terminal is connected directly to the local R.F. ground plane. In the case of a FET, the common electrode can be the source, gate or drain. In the case of a thermionic vacuum tube, the common electrode can be the cathode, grid or plate. In the case of a vacuum microelectronic device, the names are still evolving. The local R.F. ground is bypassed to the case of the package near the local R.F. input and/or output connections. This design permits double bond wires from the emitter to the local R.F. ground plane and eliminates parasitic oscillations where the potential oscillation frequency of the active device being protected is at least twice as great as the operating frequency of the package.

Abstract: A field monitor in the near field receives an antenna signal which approximates that which would be received by the monitor if located in the far field. In one aspect of the invention, the antenna signal is produced by an array of spaced apart receiving elements. In another aspect of the invention, the signal received from a near field sampling antenna is passed through a signal processor having the necessary characteristics to construct from the sample a signal corresponding to that which would have been received in the far field. Antenna element arrays are also used as plane wave sources permitting antenna testing with a radiating path length of one-eighth or one-quarter of the far field distance. Compact indoor antenna test ranges are also provided.

Abstract: Synthesizer radiating systems providing efficient wideband operation incorporate a radiating element (20a), such as a loop, dipole or whip, which has dimensions which are small relative to wavelength in the radiated frequency band. Energy dissipation is substantially reduced by cycling stored energy back and forth between a radiating element (20a) having a first reactance and a storage element (22a) having the same or opposite reactance, in order to achieve energy efficiency along the lines of a narrowband tuned-circuit antenna. Wideband operation is achieved by synthesizing a representation of an input waveform (at 28) by actively controlling (30) solid-state switching devices (24), responsive to rate control and direction control parameters, which are interactive with the energy transferred between the opposite reactances. Higher efficiencies are achieved by bipolar circuits providing separate positive and negative energy transfer paths between a radiating element and a storage element.

Abstract: Systems are provided to derive a value of barometric pressure at a defined location in the atmosphere at a computed geometric height. By using the geometric height in a look-up table of pressure/height values representing a standard atmospheric profile, atmospheric deviation data indicative of the difference between measured and reference pressures at that atmospheric location (C) is derived. Ground-based interrogators (10,20) located at spaced positions are used to initiate response signals from airborne transponders commonly installed in transient aircraft (C). Using resulting range data based on round-trip timing differences in signals sent to (12,16) and received from (16,14) the airborne transponder (C), geometric analysis and computation is used (18) to determine the geometric height of the transponder representing a specific atmospheric location.

Abstract: Mutual coupling effects, which would tend to degrade operation of a two-element end-fire array over a frequency band, are overcome by provision of an inter-element coupling impedance which is effective to equalize the Q at the inputs to the quadrature-excited elements. A quarter-wave transmission line section is coupled between the inputs to provide such impedance, which has a value selected to offset the effect of mutual coupling on Q. For a pair of monopoles, the inter-element coupling line is connected to the respective monopoles by quarter-wave sections having impedances selected in order to provide desired input impedances. The performance of dual-element end-fire slot or dipole array antennas may similarly be improved. Linear array antennas of four or more elements are provided by forced feeding of the additional elements from the basic dual-element configuration in accordance with the invention.

Abstract: Linear array antenna systems are used in X-scan aircraft location systems and methods able to avoid disabling azimuth error conditions caused by multipath reflections under roll and pitch conditions during aircraft carrier landing operations. Aircraft azimuth and elevation data is derived based upon time of incidence at an aircraft location of two transverse, diagonally oriented, scanned antenna beams. The aircraft location data is derived by comparing time of incidence data with data on known timing of scanning of the beams, which have diagonally-oriented fan beam patterns. A plurality of vertically oriented radiating elements are typically positioned along a line diagonal to the vertical to produce a diagonally oriented fan beam pattern. Beam scanning results from relative adjustment of signal portions supplied to the radiating elements.

Abstract: A compact wide-band panel antenna is modified to provide a dual-mode antenna system with improved operation, particularly in the presence of interfering signals and varying reception conditions in mobile communications applications. A hybrid junction arrangement is used to combine received signals in sum and difference modes suitable for adaptive processing. Signal transmission is provided by reciprocal operation, with a circulator incorporated for signal isolation. The dual mode capability provides previously unavailable performance in a small, economical broad-band antenna.

Abstract: A field monitor in the near field receives an antenna signal which approximates that which would be received by the monitor if located in the far field. In one aspect of the invention, the antenna signal is produced by an array of spaced apart receiving elements. In another aspect of the invention, the signal received from a near field sampling antenna is passed through a signal processor having the necessary characteristics to construct from the sample a signal corresponding to that which would have been received in the far field. Antenna element arrays are also used as plane wave sources permitting antenna testing with a radiating path length of one-eighth or one-quarter of the far field distance. Compact indoor antenna test ranges are also provided.

Abstract: The need to widely separate antennas (e.g., transmit and receive antennas) for VHF radio and other applications is avoided by high-isolation antenna systems with collocated antennas and cancellation of intercoupled signals. A transmit antenna in the form of a vertical dipole can be mounted atop a mast with a receive antenna comprising a multi-element array of vertical dipoles supported on the same mast below the transmit antenna. Opposing pairs of the dipole receiving elements are located in 180.degree. positions on opposite sides of the mast so as to be symmetrically located in the omnidirectional antenna pattern of the transmit antenna. Resulting intercoupling to the receive dipoles is equal and in-phase and is cancelled out by the antiphase combining of signals from the dipoles of each pair of the receive dipoles. Reciprocally, cancellation of coupled signals is achieved with reversal of the receive and transmit functions of the respective collocated antennas.

Abstract: Array antennas for aircraft use have a shiftable center of radiation. The antenna beam of a group of laterally spaced array antennas is steered and the beam shape is controlled by relative shifting of the centers of radiation of the arrays. Beam tilting in a fuselage mounted system of array antennas uses controlled selection of active antennas.

Abstract: Airborne navigation receivers are designed to derive navigation information with accuracy immune to beam asymmetry errors. Scanned navigation beams of the Microwave Landing System are subject to asymmetry causing beam center measurement errors at power levels other than a standard level 3dB down from peak. Dwell gate and split gate type receivers achieve error immunity through offsetting of errors at power levels above and below a standard power level.

Abstract: An antenna comprising a linear array of active elements positioned in one or more rows. The back portion of the array is partially enveloped by a reflector. The reflector includes a backwall and at least one sidewall perpendicular to the backwall and extending forward of the backwall. In one embodiment of the invention, a single row of dipole radiators form the linear array. In a second embodiment of the invention, a row of folded monopoles mounted on an imaging ground plane form the linear array. The radiation pattern is directed forward of the reflector, the back radiation in the E-plane being suppressed by the sidewall of the reflector.