摘要:
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.
摘要:
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.
摘要:
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. Arrangements for use of the invention with two-dimensional-scan and one-dimensional-scan phased arrays are also described.
摘要:
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.
摘要:
Aircraft-mounted Identification Friend or Foe (IFF) antennas employ a linear array of radiator elements positioned transverse to the boresight axis. With an azimuth determination capability, but lacking elevation resolution, such antennas are subject to coning errors in determining the azimuth bearing of a target at an altitude differential. With use of a linear array (10) of multi-radiator elements (11, 12, 13), an output signal (23) having the characteristic of an amplitude which increases for off-boresight targets is provided. That signal is compared to a typical form of antenna system output signal (22), which has an amplitude which decreases for off-boresight targets. By such amplitude comparison, the angle (.beta.) to a target is determined and used to provide an azimuth correction factor (53). An apparent azimuth bearing (54) subject to coning error can then be corrected (55) to provide the true azimuth angle to a target (56).
摘要:
The usable range of incidence angles for electromagnetic wave polarizers using arrays of polarizer elements is increased by introduction of a dielectric medium having a dielectric constant large enough to reduce the angle of wave incidence upon the polarizer elements. For example, arrays of 45 degree inclined meander-line polarizer elements are encased in a dielectric medium having a dielectric constant of about 3. The polarizer includes impedance matching layers at the surfaces of the dielectric medium to reduce reflections at those surfaces. The resulting polarizer is indicated to be usable to reciprocally convert an incident polarization to a desired polarization (e.g., from linear to circular polarization) for waves with incidence angles from zero to 70 degrees in any plane.
摘要:
The isolation of mainbeam and sidelobe jamming signals from the desired signal being relayed by microwave communication links is accomplished by an antijamming antenna comprising a flat radome, a curved reflector and a transmit dipole. Positioned adjacent the dipole is a monopulse feed and comparator for main-beam jammers (dual-plane monopulse, multi-mode multilayer feed). Also forming part of the integrated antenna are auxiliary units for near-sidelobe and far-sidelobe jammers. An alternative embodiment includes a Cassegrain grating sub-reflector. Since the direction of the desired incoming signal in microwave communication links is precisely known, the antijamming antenna uses azimuth and elevation monopulse to make a spatial distinction between the desired incoming signal and the jamming signals. The antijamming antenna system outputs: a sum, azimuth difference elevation difference signals and isolated near-sidelobe jamming signals and far-sidelobe jamming signals on output ports which allow an adaptive processor to place pattern nulls on jammers located in the mainbeam and sidelobe region of the antenna.
摘要:
Low profile array antennas for aircraft achieve improved performance with excitation circuits providing forced excitation of radiating elements to generate signals of desired relative phase and amplitude at the elements. Excitation circuits are structured for use of reactive turning for wideband operation. Monopole or slot array antennas, each including three or more radiating elements, can be grouped as antenna systems.
摘要:
A central aperture provides at least two radiation pattern modes. A second aperture concentric with the central aperture provides at least two radiation pattern modes. A first feed system excites the central aperture and a second feed system excites the concentric aperture. Circuit means associated with the second feed system provides an auxiliary excitation to the concentric aperture which results in optimizing the radiation pattern obtained during excitation of the central aperture.
摘要:
An angular filter for electromagnetic radiation is formed of a set of elements supported on a dielectric substrate. The elements are electrically conducting and include resistance for dissipating energy of the radiation. Each element is formed as a closed loop in a plane normal to an axis of propagation of the radiation so as to minimize interaction with a transverse magnetic field of the radiation at zero angle of incidence to the filter, the interaction and consequent attenuation increasing with increasing angle of incidence. Thereby, spurious sidelobes of a radiation pattern associated with a radar or other antenna can be reduced by the filter in favor of the main lobe along the antenna axis. The elements may be formed by a set of members spaced apart to introduce capacitance for resonating with inherent inductance of the members, thereby to enhance the filter attenuation.