Other

Hughes Aircraft Company

Hughes Electronics Corporation

David A Whelan

Gregory M Gutt

Brian M Pierce

John Fraschilla

Thomas K Dougherty

James R Chow

Norman H Harris

David G Lawrence

Henry L McCord

Michael L O'CONNOR

A passive imaging system that uses an antenna having two antenna elements. The system cross-correlates received signals with a reference function to achieve high resolution. The antenna elements are rectangular with their long dimensions oriented normal to the longitudinal axis of a carrying vehicle and the elements are separated by a distance consistent with image resolution requirements. Additionally, the antenna elements are frequency scanned in the cross-track dimension. The channel for the forward antenna element has a time delay relative to that of the rear antenna element. This time delay achieves pointing of the antenna at a particular forward angle relative to the normal to the velocity vector. Outputs of IF filters of the antenna elements are synchronously detected to provide in-phase and quadrature (I/Q) components of their phase modulated product. These I/Q components are processed by an analog-to-digital converter and digitally filtered to select a phase modulation frequency band about the chosen forward angle. The real pan of the output of the digital filter is stored and is the cross-track channel signal is cross-correlated with the reference function. The output of this cross-correlation provides high along-track resolution with suppressed along-track sidelobe responses. The reference function is a weighted, limited-extent, replica of the real pan of the phase of a small-area signal as such signal passes through the forward angle. The reference function weighting suppresses correlation function sidelobes and is adjusted to include a component introduced by the bandwidths of the IF receivers, the angle extent that is used, and the separation between the antenna elements. A separate set of processing circuits is provided in parallel for each cross-track image channel at the output of the intermediate frequency (IF) amplifiers of both antenna elements. A fixed bandwidth is provided in each cross-track image channel, but the center frequency is different in order to point the beams of the antenna elements at a chosen cross-track position.

Correlation radiometer imaging system

Ferro-electric frequency selective surface radomes that have dielectric layers that comprise voltage controlled material, and the electrical properties of the dielectric layers are voltage controlled. By varying the dielectric properties, the passband frequency of the radomes can be shifted to optimize frequency and angular response of the frequency selective surface. The radomes comprise grating screens having a plurality of printed radiating elements. Inner and outer voltage controlled dielectric layers are disposed on the grating screens. Relatively high ohms per square resistive films are disposed on exposed surfaces of the voltage controlled dielectric layers. In one embodiment, voltage control circuitry is coupled to the respective resistive films for controlling the voltages applied to the respective voltage controlled dielectric layers by actively varying the dielectric permittivity of the resistive films around a small percentage of its nominal value to provide a ground on outer surfaces of the dielectric layers. In another embodiment, the ferro-electric frequency selective surface radome may comprise voltage controlled dielectric layers disposed on one surface of the grating screens. Voltage control circuitry is coupled to the first and second grating screens for controlling the voltages applied thereto and thus the performance of the radome.

Ferro-electric frequency selective surface radome

A microwave-absorbing material composed of blends of polar icosahedral molecular units with a variety of host matrices, or with polymers with the units covalently bonded in a pendant manner to the polymer chain. Both blends and polymers must impart a high degree of orientational mobility to the units so that they can absorb microwave radiation. These materials employ orientationally mobile, polar icosahedral molecular units as the source of dielectric loss at microwave frequencies. Examples of these units are the polar carboranes (ortho- and meta-carborane), polar carboranes with electronegative and/or electropositive substitutes, and polar 'buckminsterfullerenes.'

Microwave-absorbing materials containing polar icosahedral molecular

An impregnated carbon film expanded into a honeycomb structure is employed in a tapered notch phased array antenna and is used to absorb cross-polarized incident fields to reduce the reflections from shorted TEM parallel plate modes existing between radiator elements of the antenna. The carbon loading used to achieve this absorption may comprise a resistive taper, or analog circuit or anisotropic elements having a predetermined tapering resistive profile. The honeycomb cross-polarized load of the present invention provides the electrical performance necessary to meet tapered notch phased array antenna electrical requirements while reducing the weight and cost of antennas in which it is employed.

Honeycomb cross-polarized load

An asymmetrical notch radiating element comprising a metal or metal-clad dielectric substrate into which a tapered slot or notch is disposed. The direction of the axis of the tapered slot lies along any preselected axis and is not constrained to be collinear with the normal to the aperture of the element. An asymmetrical antenna array comprises a plurality of asymmetrical notch radiating elements as described above. Each of the plurality of radiating elements is disposed such that the apertures of each of the elements are substantially coplanar and are at an angle relative to the notch axis. The present antenna uses asymmetric slot lines to control the antenna's electrical performance. The precise slot dimensions are chosen to optimize radiation and reduce scattering. The asymmetric flared notch allows optimization of the transmit gain in a direction that is not necessarily normal to the array surface. The asymmetrical notch radiator is designed for use in phased array antennas where reduced radar cross section and wide bandwidth are essential, or in conformal arrays, where the surface normal and array axis are not collinear. The normally high specular radar reflection from the antenna radiators, that lies along the array normal, no longer points in the same direction as the peak antenna gain. This allows the design of a low radar cross section array antenna that does not suffer poor gain due to its reduced cross section.

Growing community of inventors

Chatsworth, CA, United States of America

David A Whelan