Abstract: GPS reception on helicopters and ground vehicles may be subject to varying near-ground interference. A compact antenna includes vertically spaced arrays of radiating elements. The first array provides a basic reception pattern. The second array provides a pattern having a distinctive low elevation angle phase reversal. By combining signals for these patterns an antenna pattern with a low angle onmidirectional elevation null characteristic is provided to suppress near-ground interference. Prior to combining, signals from the second array may be modified in amplitude or phase, or both, on a semi-permanent basis, or may be adaptively modified on an active basis, in order to adjust the null characteristic. Antennas and methods are described.

Abstract: An antenna, suitable for battlefield identification use, employs a multifunctional design. A closed-end coaxial line structure with center conductor has slanted slot radiators provided in its outer conductor. The slot radiators excite a pattern between upper and lower disks of a radial waveguide radiator configuration so that horizontal and vertical components reach the disk circumference with a 90 degree phase differential to provide an omnidirectional antenna pattern of circular polarization. Antennas and methods are described.

Abstract: An antenna, suitable for battlefield identification use, employs a multifunctional design. A closed-end coaxial line structure with center conductor has slanted slot radiators provided in its outer conductor. The slot radiators excite a pattern between upper and lower disks of a radial waveguide radiator configuration so that horizontal and vertical components reach the disk circumference with a 90 degree phase differential to provide an omnidirectional antenna pattern of circular polarization. Antennas and methods are described.

Abstract: The integrity of operation of a GPS precision aircraft approach and landing system may be compromised by error producing effects of reflected multipath signals. An integrity monitor antenna system as disclosed may utilize both attenuation and shadowing of reflected multipath GPS signals to achieve extreme multipath mitigation of the order of 50 dB suppression. An antenna with a right-hand circular polarization pattern having a sharp cut off at the horizon may provide 30 dB suppression of reflected multipath signals. A signal absorbent ground plane bed of defined dimensions may provide 20 dB attenuation of incident multipath signals. A signal/processor may be employed to derive position error data for integrity monitoring, based upon differentials between a known fixed location and a current GPS-indicated location. Communication of identification of a subset of particular GPS satellites for common usage may also reduce potential error levels.

Abstract: Accuracy of derivation of local corrections to GPS signals for use for aircraft landing guidance is subject to effects of reflected multipath signals. Antennas with a near-spherical antenna pattern of right-hand circular polarization, except within a downward cone, provide suppression of reflected multipath GPS signals incident from all azimuth angles and all relevant elevation angles. For such an antenna a cylindrical top assembly may include spaced conductive disks with intermediate exciter members excited at increments of 90 degree phase and surrounded by a dielectric ring. A cylindrical base assembly may include signal absorbent top and side wall portions and a bottom conductive disk and may alternatively include a signal absorbent inner wall portion.

Abstract: GPS reception on helicopters and ground vehicles may be subject to varying near-ground interference. A compact antenna includes vertically spaced arrays of radiating elements. The first array provides a basic reception pattern. The second array provides a pattern having a distinctive low elevation angle phase reversal. By combining signals for these patterns an antenna pattern with a low angle onmidirectional elevation null characteristic is provided to suppress near-ground interference. Prior to combining, signals from the second array may be modified in amplitude or phase, or both, on a semi-permanent basis, or may be adaptively modified on an active basis, in order to adjust the null characteristic. Antennas and methods are described.

Abstract: Vertical array antenna systems can provide broadband data link operation with reduction of susceptibility to low angle multipath effects, for communication during carrier landings by aircraft and other applications. In a relatively small package, an antenna system may include a stack of sub-arrays, each including four dipoles provided as configurations of downward and upward extending dipole arm members which are vertically separated by an annular slot excited by vertical probes. Excitation of the dipoles may be provided via excitation of the annular slot by the probes. Intercoupling-reduction disk units may be positioned between vertically adjacent sub-arrays. Pattern cutoff characteristics suitable for aircraft carrier landing operations (e.g., for reliable DGPS communications) at or near the horizon may be provided by excitation of individual sub-arrays at predetermined relative levels and with pattern phase reversal between lower and upper sub-arrays.

Abstract: A GPS antenna with anti-jam capabilities utilizes eight resonant loop radiator elements in a resonant exciter configuration to make available a primary and up to seven auxiliary antenna patterns usable with multi-pattern adaptive processing for anti-jam operation. Antennas as described enable desired radiation characteristics to be provided in a configuration of small size suitable for replacement of existing GPS aircraft antennas which lack anti-jam capabilities, in order to enable reliable GPS reception during airborne operations in the presence of interference or jamming. With enablement of multi-pattern adaptive processing, reduced-gain pattern notches or nulls may be employed to track and reduce the effect of incident signals which would otherwise jam or interfere with reception of GPS signals.

Abstract: Ground based GPS antennas for differential applications may be subject to intentional or other interference signals incident at low elevation angles. Described GPS antenna systems are usable to provide an antenna pattern having a vertically-steerable null. An array of vertically spaced radiator units having omnidirectional azimuth characteristics provides a primary reception pattern. Vertically intermixed radiator units employed on a separate or shared basis provide an auxiliary reception pattern. By subtractively combining the auxiliary pattern with the primary pattern and adjusting the relative signal level of the auxiliary pattern a vertically-steerable pattern null is provided. The antenna system may include an adaptive control system responsive to an antenna output signal to derive a steering signal to adjust the relative signal level of the auxiliary pattern to steer the vertically-steerable null to provide interference suppression. Antenna systems and methods are described.

Abstract: Dual-array two-port GPS antenna systems can provide horizon to zenith reception for differential GPS applications. On a single mast, an antenna system may include a lower array of sub-arrays (e.g., fifteen sub-arrays) to provide elevation coverage from horizon up to about 55 degrees elevation and an upper array of sub-arrays (e.g., three sub-arrays) to provide elevation angle coverage from zenith down to about 55 degrees elevation. Each sub-array may be of the same construction including four dipoles positioned at different azimuth locations and configured to provide a progressive-phase-omnidirectional (PPO) azimuth pattern suitable for reception of circularly polarized signals. In a particular embodiment the three sub-arrays of the upper array have PPO azimuth patterns with differing azimuth alignments and differing excitation values to provide a desired elevation angle coverage characteristic.

Abstract: Flat-plate antennas have a compact form by use of a folded path network construction whereby received signals are coupled through a unitary network structure to an adjacent signal processing unit. On a folded path basis, processed signals are then coupled back into the network structure, combined with other received processed signals and then passed out of the network structure to an adjacent signal port. The signal processing unit may provide either amplification, phase shifting, or both. By reciprocal operation a signal to be transmitted may be divided into sub-array components, processed (e.g., power amplified and phase shifted), further divided, and coupled to each slot radiating element (e.g., 256 slots) of an array of slot sub-arrays.

Abstract: Improved punch-through performance is provided for applications such as sum and difference mode processing for IFF and other applications. With an array including a row of elements, difference sidelobe levels are increased relative to sum sidelobe levels by independently controlling relative signal levels of difference mode signals provided from signals received by central elements of the array. By processing signals from central elements independently from processing of signals from outer elements of the array, difference mode signals derived from the central elements may be employed at higher signal levels in order to raise difference mode sidelobe levels to improve punch-through performance. Antenna systems and methods are described.

Abstract: An antenna system to enable satellite communication with a moving vehicle, such as an aircraft, includes an array formed by a group of subarrays. The array is positioned within a cavity and arranged to be mechanically tilted about a horizontal axis-of-rotation to provide elevation scanning of an antenna beam pattern (e.g., 20 to 90 degree elevation scan). The array, with the cavity, is mechanically rotated to provide azimuth scanning of the beam pattern (e.g., 360 degree azimuth scan). Each subarray may be a square flat-plate array having slot-type radiating elements (e.g., simple or crossed-slot elements). Equal excitation of the subarrays for receive or transmit may be provided by a feed configuration at the back of the array.

Abstract: An antenna system, to enable communication with a moving vehicle via a satellite, utilizes an array of subarrays contiguously positioned in a diamond-type pattern. Straight edge boundaries of an array can maximize sidelobe degradation resulting from diffraction effects at the edge. The diamond-type array pattern provides saw tooth array edge boundaries with all edge portions at 45 degrees (or other suitable acute angle) to the principal array dimension (the length dimension). Uniform excitation may be provided for all subarrays via a binomial power divider/combiner configuration. Mechanical beam steering can be provided in azimuth and elevation. A phase shifter assembly may be provided to enable a limited electronic scan (e.g., plus or minus 2 degrees) to increase beam steering agility from a moving vehicle. Thin flat-plate subarray design details are provided.

Abstract: Antennas having a circular array of radiating elements are arranged to enable continuous 360 degree scanning of a sum and difference beam pattern. With a 108 element circular array, a sub array of 27 contiguous elements may be step scanned to 108 positions while maintaining sum and difference antenna patterns. Each scan step may require only two switch adjustments, one to initiate excitation of a contiguous leading element and terminate excitation of the trailing element, and the other to change coupling of a middle element from a divided power port of a left power divider to such a port of a right power divider. Configurations using sub arrays whose element complement is not evenly divisible into the total number of array elements, using sub arrays consisting of an odd number of radiating elements, or employing minimized feed network complexity are disclosed.

Abstract: A reduced-size GPS antenna with anti-jam capabilities includes eight inclined monopole elements making available a primary and seven auxiliary antenna patterns usable with multi-pattern adaptive processing for anti-jam operation. An excitation network coupled to the eight monopole elements can be configured to provide the eight antenna patterns having quadrature characteristics with low mutual coupling. Bent monopoles or other elements may also be utilized. With availability of the primary and auxiliary patterns, multi-pattern adaptive processing can be employed during airborne operations to actively provide reduced-gain pattern notches or nulls to track incident angles of interference or jamming signals. In other embodiments selected combinations of less than all of the eight antenna patterns or other patterns may be employed.

Abstract: To provide horizon to zenith reception coverage for Differential GPS operations, two antennas with complementary patterns may be used. An antenna for high-angle coverage includes a ring of four dipoles excited to provide progressive-phase-omnidirectional (PPO) coverage. A cylindrical (e.g., octagonal) structure, with an upper edge at the diode horizontal centerline, extends upward from a ground plane section. An absorber configuration having a serrated upper edge portion extends around the dipoles above the cylindrical structure and has radiation absorption properties. For an octagonal configuration, the absorber configuration may include eight resistance card sections with triangular portions extending above the wall structure. A conical antenna pattern expanding upwardly can provide omnidirectional coverage above a selected elevation angle (e.g., above 55° elevation).

Abstract: A whip antenna with switchable operative length provides seven band coverage from 30 to 90 MHZ. A coaxial choke section below a fixed upper antenna element is used for the highest frequency band. A series of four coaxial line sections are switchably coupled below the choke section to increase its operative length for operation in bands of successively lower frequency. One or more lumped constant non-coaxial transmission line sections are switchably coupled below the coaxial line sections for operation in the two lowest frequency bands. Dipole level gain is provided with low reflections loss. Increased height gain is provided by height of operative antenna elements employed at higher frequency bands.

Abstract: A compact aircraft antenna for reception of GPS signals includes eight elements to provide eight antenna patterns usable for anti-jam signal processing. Four bent monopole elements are configured with vertical portions and horizontal inward-extending portions. The bent monopole elements are arranged for multimode excitation to provide a primary progressive phase omnidirectional right-hand circularly-polarized antenna pattern for basic signal GPS signal reception. Multimode excitation of the bent monopoles also provides omnidirectional left-hand circularly-polarized, uniform phase omnidirectional, and clover leaf auxiliary antenna patterns. Four individual slot element figure-eight type auxiliary antenna patterns are also provided. With availability of these primary and auxiliary patterns, adaptive type anti-jam processing can be employed to actively provide reduced-gain antenna pattern notches or nulls at incident angles of interference or jamming signals.

Abstract: A source of interference signals may be present at a fixed incident angle relative to a stationary antenna. Horizontal array antennas are provided with radiation pattern notches or nulls at selected fixed angles to suppress reception of interference signals. By excitation of elements on the left side of an array in opposite phase relative to elements on the right side and provision of an appropriate line-length differential between left and right radiation element feed lines, a radiation pattern notch is positioned at a selectable angle relative to boresight. Notch width optimization is provided by use of relative excitation levels of radiating elements as disclosed. Other configurations are disclosed.