Hughes Aircraft Company

Joseph G Gurley

Kar W Yung

Donald C Chang

Frank A Hagen

Samuel C Reynolds

Urban A Van Der Embse

A technique for near-field tomographic imaging using a multiple-receiver correlating interferometer. A target object or scene to be imaged is located in a near-field or Fresnel region of a receiver system. The target object radiates or reflects a signal that is sensed by a plurality of antennas. The received signals are correlated using conventional correlation algorithms. An image pixel for a focal point is then computed by correcting a differential time delay between a signal emitted at the focal point and received at first and second antennas. The system is focused on the target object by correcting a phase term of the correlation algorithms. The phase term is corrected by multiplying the correlation algorithms by a phase factor. A peak correlated value is developed when the focal point is at the target object location. A series of snapshots is generated from data produced by the focussing process, as the focal point is moved through the scene. The snapshots are successively superimposed, using tomographic techniques, to form a high resolution image map. The system achieves extremely high resolutions, rivalling those of synthetic aperture radar.

Passive microwave near-field tomographic imaging system and method

An efficient digital beam-forming network (100) utilizing a relatively few small-scale A/D converters is disclosed herein. The inventive beam-forming network (100) is disposed to generate an output beam B in response to a set of N input signals. The set of input signals is provided by an antenna array (110) having N elements, upon which is incident an electromagnetic wavefront of a first carrier frequency. The present invention includes an orthogonal encoder circuit (170) for generating a set of N orthogonal voltage waveforms. A set of biphase modulators (162-168) modulates the phase of each of the input signals in response to one of the orthogonal voltage waveforms, thereby generating a set of N phase modulated input signals. The N phase modulated input signals are combined within an adder (180) to form a composite input signal. The inventive network (100) further includes a downconverting mixer (184) for generating an IF input signal in response to the composite input signal. The IF input signal is then separated into baseband in-phase and quadrature-phase components by an I/Q split network 192. A pair of A/D converters (198, 200) then sample the in-phase and quadrature-phase components of the input signal. A decoder (202), coupled to the orthogonal encoder circuit (170), provides decoded digitial in-phase signals and decoded digital quadrature phase signals in response to the digital in-phase and quadrature-phase signals. The present invention further includes a digital beam-former (130) for generating the output beam B by utilizing the decoded in-phase and quadrature-phase signals.

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Los Angeles, CA, United States of America

Joseph G Gurley