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.
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:
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:
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. Four beams are provided by a beam forming network arranged to couple antenna element signal feeds to the four upper radiators and corresponding reverse phase signal feeds to the four lower radiators.
摘要:
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.
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:
An array of axially oriented thin resistive elements having a certain value of conductance or resistance in the axial direction is supported in dielectric material. For a wave at normal incidence, the apparatus is essentially invisible. For a wave incident at oblique angles in the E plane, current is induced in the resistive elements and dissipative attenuation occurs. The attenuation does not rely on resonance so that the apparatus operates over a wide frequency band and does not require tight dimensional tolerances.