Air Force

Radar combining synthetic aperture mode with moving target identification

Enables signals of multiple classes to be radiated and utilized at the same time including synthetic aperture radar signals with ground moving target indication signals, or communications signals simultaneously with radar signals

Communications Sensors

Synthetic aperture radar (SAR) is a form of radar that is used to create two- or three-dimensional images of objects, such as landscapes, and requires a wide bandwidth waveform. SAR uses the motion of the radar antenna over a target region to provide finer spatial resolution than conventional beam-scanning radars. SAR is typically mounted on a moving platform such as a plane. In contrast, moving target indication (MTI) is a radar technique that discriminates a target against background. It describes a variety of ways to find moving objects, like an aircraft, and filter out unmoving ones, like hills or trees.  MTI employs a relatively narrowband signal at a fixed location. Beside beam-width, the two radar functions also specify differing pulse repetition frequency requirements and these different demands require that SAR and MTI be performed either sequentially or using separate systems.

For reasons of gaining increased intelligence from an image, efficiency, smaller footprint and leveraging of hardware, Air Force scientists and engineers have developed a method and device to generate SAR and MTI data at the same time.

The breakthrough utilizes independent waveform generation, timing, and control across multiple apertures in a phased-array radar set up. Waveform generation produces narrowband waveform building blocks, or basis functions and these basis functions are radiated from different antennas or elements. This permits the simultaneous transmission of multiple waveforms at different frequencies, as opposed to sequential transmission of waveforms for varied functions.

Moving target indication is applied at the building block level. An M-pulse Doppler processor is applied after M−1 two-pulse cancellers for each aperture. Doppler compensation is applied across apertures to scale for different frequencies for each spatial channel. Integration is then performed across apertures.

Wideband synthetic aperture radar waveforms are synthesized from the narrow band components across space and time utilizing interpolation and extrapolation. Monostatic and N−1 bistatic synthetic aperture radar images are formed for each of N channels. Integration is then performed across apertures and pulses. The process therefore results in simultaneous moving target indication and synthetic aperture radar.

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