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 90 degree azimuth beamwidth is achieved in a narrow cellular antenna, by inclusion of sidewalls. To improve front-to-back performance, slot radiating elements extending through the sidewalls re-radiate signals behind the antenna. Signals re-radiated from the slot elements are effective to partially cancel signals otherwise radiated behind the antenna as a result of diffraction. H-shaped slots are described for sidewall use and side-to-side slots are described for endwall use. Slots may be dielectrically loaded by contiguous portions of a radome.

Abstract: Performance of multibeam cellular antenna systems is improved by use of space diversity in antenna placement and angle diversity in antenna alignment. Space/angle diversity is achieved on a single tower structure (20) by placement of eight antennas (B1-B8) in pairs at four spaced locations (I, II, III, IV) at the tower corners. Antennas are placed with an orthogonally directed pair at each location. For each orthogonal pair (e.g., B1 and B2 at location I) there is an antenna located at a different corner which is pointed between the orthogonal directions (e.g., B5 at location II). Antenna placement and alignment for achieving space/angle diversity in triangular tower configurations are also described.

Abstract: An interleaved planar array antenna system providing angularly adjustable linearly polarized beams comprises an array of parallel rows of transmit dipole element pairs and an array of parallel rows of receive dipole element pairs, the two arrays being interleaved. Each of the dipole element pairs includes a first dipole element and a second dipole element adjacent and orthogonal to the first dipole element. All of the first dipole elements are parallel to each other and all of the second dipole elements are parallel to each other. All of the dipole elements are on the same surface and on another surface parallel to and spaced from the first surface there is an array of transmit feed line pairs and an array of receive feed line pairs, with the arrays being interleaved with each other. The transmit feed line pairs are proximity coupled to the transmit dipole element pairs and the receive feed line pairs are proximity coupled to the receive dipole element pairs.

Abstract: A multifunction antenna system is selectively operative over the UHF and VHF frequency ranges using a novel arrangement of symmetrically disposed phased radiating elements that function as a dipole turnstile type array at UHF and as a monopole at VHF. At VHF the UHF radiating elements and feedlines are fed in parallel against ground to produce a pattern similar to that of a short vertical monopole. VHF and UHF coupling networks offer low VSWR and minimize circuit losses when utilized with a folded dipole array. The compact, lightweight structure is adaptable to oceanic communications by installing in a towed radome adapted for water flotation, and provides low angle hemispherical UHF radiation without pattern switching, with the water surface providing a reflective ground plane.

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: When establishing a link (i-j) between two nodes i, j in a mobile radio communications network, transmission parameters are assigned such that conflicts and interference with nodes that neighbor the nodes i and j are avoided. A time-slot and a frequency-code value are assigned to the link (i-j) from a defined set of time-slots T, and from a defined set of frequency-code values FC. Set T contains time slots (t) during which links in the network can be activated, and set FC contains frequency-code values (f, c) each of which specifies a frequency or a frequency-code pair for association with the links. A time slot t.sub.k is first chosen from set T which slot is not in use for links between node i and nodes neighboring node i, or for links between node j and nodes neighboring node j. A frequency-code value (f, c).sub.1 is next chosen from set FC which value is not in use by any node that neighbors node i or by any node that neighbors node j, during the chosen time slot t.sub.k.

Abstract: Where two or more antenna beams may receive signals from the same cellular communication system user, post-reception beam channel gain variations may obscure choice of the channel providing the strongest user signal. Thermal atmospheric noise, assumed to equally enter each beam, is utilized as a standard signal level in order to calibrate the relative gain factor for each channel. Thermal noise level is measured by use of a single common receiver (32) sequentially coupled to each channel (22-25) to listen for lowest signal levels during inactive intervals, over periods of time which may extend for hours. Lowest signal levels provide thresholds for each channel from which gain correction factors are developed. When a user signal is received in two channels, the gain correction factors are employed to select the channel providing the best signal, on a substantially real time basis. A long-term lowest signal level monitoring algorithm is described.

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: A relative time offset is measured between transmission of a downlink signal from a cellular radio network base station, and a reference signal (e.g., sync word) included in an uplink signal received at the base station from a network subscriber. If the measured time offset is within a determined range, the uplink signal is judged to originate from a subscriber which is validly assigned to the base station, and the base station will continue to track the valid uplink signal. If the relative time offset is outside the determined range, the uplink signal is judged invalid, e.g., to originate from an interfering co-channel subscriber assigned to a remote base station. The receiving base station will then inhibit tracking of the invalid uplink signal.

Abstract: A volumetric/planar array structure for detection of low frequency active pulses in shallow water. The structure is such that the array can be repeatedly deployed and retrieved. The invention utilizes folding array arms that are deployed at a pre-selected depth using only gravity once the release mechanism for deployment has been initiated. Rigid vertical support rods attach to all array levels preventing rotation down below the desired horizontal position during operation. Retraction of array arms for array structure retrieval is initiated by activating an electronic underwater release mechanism which then allows compliant rubber members to pull array arms in place. Once the array arms are in place, they are protected by a skid/crash cage fixture and the array structure is then ready for retrieval.

Abstract: An architecture for a radio network having nodes that are subject to dynamically changing topology such as, e.g., a mobile radio network. The network is partitioned into a number of physical subnets wherein each physical subnet includes a certain number of network nodes in relatively close proximity to one another. Each node of each physical subnet is affiliated with a corresponding node of each of the other physical subnets, thus defining a certain number of virtual subnets. A desired communications path is routed from a source node of one physical subnet to a destination node of another physical subnet, by routing certain parts of the path within one or more physical subnets during a first transmission phase, and routing remaining parts of the path within one or more virtual subnets during a second transmission phase.

Abstract: Thin panel antennas, suitable for mounting on the side of a building, display a graphic representation and coloration compatible with the surface form and coloration of the building. A graphic display structure functions as a radome covering the front of an antenna utilizing slot arrays or other radiating elements. The graphic representation positioned on such display structure provides an image and coloration which may simulate the surface form and coloration of the building, simulate a structural feature, or otherwise provide a compatible visual relationship with a building or other structure.

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: In a communication system, two multi-beam antennas laterally spaced from each other each provide coverage of an azimuth sector for receiving signals from a system user. Each antenna provides lower gain performance at regions of crossover between its beams, as compared to peak gain along the center line of each beam. By aligning the two multi-beam antennas at different azimuths within the sector of interest, angular diversity is achieved. With the peak gain beam center lines of one multi-beam antenna aligned with regions of beam crossover of a similar antenna, a minimum gain improvement of 5 dB may typically be obtained with two four-beam antennas, as compared to coverage of the same sector by one or more antennas each having a single sector-wide beam. Systems and methods for achieving angular diversity/spaced diversity operation are described.

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.