United States of America As Represented by the Secretary of the Air Force

Earth Sounding International

Van Etten, Paul

Brown, Russell D.

Russell D Brown

Michael C Wicks

Paul Van Etten

Scott M Bolen

William J Baldygo, Jr

Donald D Weiner

Spatial-temporal waveform diversity methods vary or modulate the far-field radiated waveform of a radar and/or communication antenna as a function of look direction (sidelobe structure). Radar detection performance and angle of arrival estimation are enhanced to deny a coherent reference to non-cooperative bistatic radars and coherent repeater jammer systems. In the most general case, the spatial-temporal modulated waveform varies as a function of angle, based upon the principles of multi-dimensional Fourier synthesis. Spatial-temporal denial is achieved with as few as two auxiliary antennas bracketing a main antenna. The same methods for spatial-temporal waveform diversity can also embed communications signals into the transmitted radar waveform for one-way simulcast of both waveform types. These same directionally dependent simulcast waveforms can incorporate navigation signals for enhanced precision engagement.

Waveform diversity for spatial-temporal denial of radar and communication system

An artificial intelligence system improves radar signal processor performance by increasing target probability of detection and reducing probability of false alarms in a severe radar clutter environment. This utilizes advances in artificial intelligence and expert systems technology for the development of data analysis and information (signal) processors used in conjunction with conventional (deterministic) data analysis algorithms to combine radar measurement data (including observed target tracks and radar clutter returns from terrain, sea, atmospheric effects, etc.) with topographic data, weather information, and similar information to formulate optimum filter coefficients and threshold tests. Present fielded radar systems use one CFAR algorithm for signal processing over the entire surveillance volume. However, radar experiments have shown that certain CFAR algorithms outperform others in different environments. The system intelligently senses the clutter environment, and selects and combines the most appropriate CFAR algorithm(s) to produce detection decisions that will outperform a processor using a single algorithm. The invention provides for improved performance through the application of rule-based and data-based expert system computer software technology to CFAR signal processors, thereby improving target detection by reducing processing losses which result from a mismatch between the single, fixed CFAR processor and dynamically changing environment in which a radar must operate.

Expert system constant false alarm rate (CFAR) processor

An earth probing system uses deep penetration of electromagnetic waves into soil and other media. Advantage is taken of the lower attenuation of radar waves in soil by frequencies of about three megahertz or less. Bursts of electromagnetic energy of various frequencies in this range are consecutively transmitted. The transmitting antenna is continuously tuned, so as to maintain resonance during each burst, allowing large circulating currents and high power output. In a receiving antenna system, a dual antenna arrangement is providing for obtaining improved reception. A corresponding dual antenna circuit employs 'spatial notch filtering', automatic adjustment of antenna gain-frequency variations, as well as compensation for transmitter gain variation. The system may be implemented in a totally analog, totally digital, or hybrid manner. Preferably, a signal processing method detects and digitally samples signals reflected from subsurface layers and buried objects. The invention provides means for removing system distortions and interfering signals, for compensating for aliasing errors and frequency-dependent antenna gain and phase variations, and for avoiding masking errors introduced by strong reflections.

System and method for earth probing with deep subsurface penetration

A radar system that includes an ultra wideband radar signal processor for electronically scanned arrays that utilizes frequency offset generation (FOG) to achieve beam steering as compared with phase shift and time delay techniques of conventional radars. The device comprises a transmit antenna, a chirp generator connected to the transmit antenna and a first summing circuit, a receiver antenna connected to the first summing circuit, a Doppler de-ramping chirp circuit connected to a second summing circuit, the output of the second summing circuit connected to an amplitude and weighting circuit and the output of the amplitude circuit connected to a spectrum analyzer of a Fast Fourier Transform (FFT) circuit. The signal processing consists of mixing the target returns with the transmitted signal to obtain a video beat note signal. This video beat note signal is mixed with a Doppler de-ramping chirp waveform which is matched to the desired target velocity. The output is amplitude weighted and the FFT algorithm applied. To achieve beam steering for the detection of off boresight targets, a phased array with distributed receivers is required. Also, frequency offset generation must be incorporated into the Doppler de-ramping chirp generator.

Ultra wideband radar signal processor for electronically scanned arrays

A system is disclosed for use with radar systems so as to reduce the dynamic range requirement of the analog to digital converter through analog clutter cancellation prior to digitization. Clutter return estimates are formulated via modern digital signal processing techniques, converted to analog representation, and subtracted from the received waveform. Typically, the MTI cancellation is performed on the quadrature components of the received signal. The complex residue is then processed for target detection. This quadrature processing is not illustrated in the figures. In practice, sampling the received waveform prior to baseband down conversion, at an intermediate frequency, is also feasible. Digital synchronous detection and coherent MTI processing are then implemented in the digital signal processor. Rather than employ a radar signal processor which is either all analog or all digital it is beneficial to utilize hybrid schemes which capitalize on the advantages of both. A hybrid system is disclosed in which the acoustic delay line, which fundamentally limits analog MTI canceller performance, is replaced by a digital delay line. In effect, the transmitter crystal, delay medium, and receiver crystal are replaced by the analog to digital converter, digital delay, and digital to analog converter. The hybrid clutter canceller with digital processor and analog waveform synthesizer utilizes modern signal processing techniques to estimate the clutter return which is subtracted from the incoming analog signal. The full dynamic range of the received signal is not presented to the analog to digital converter, reducing the number of bits required for target detection in clutter. In effect, application of the hybrid clutter canceller reduces the A/D converter probability of saturation for a given A/D converter.

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Holland Patent, NY, United States of America

Russell D Brown