Westinghouse Electric Corporation

Northrop Grumman Systems Corporation

USA As Represented by Secretary of the Navy

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

Henry E Lee

Martin J Decker

Francisco J Guillen

David L Richardson

James H Mims

Scott Alan Stratmoen

Norman F Powell

R Noel Longuemare, Jr

David R Iny

Giora A Bendor

Stephen Warejko

Mark D Stenoien

Michael B Seldes

An airborne radar interrogates tags on friendly ground vehicles, which when interrogated by a downlink signal from the radar, sends back a very low level uplink message signal that appears noise-like so as to avoid enemy detection and exploitation. This is achieved by retransmitting a time delayed and phase shifted version of the transmitted pulse from the radar. The digital RF tag captures every other pulse from the radar and transmits a digitally coded spread spectrum pulse back to the radar during every other intervening pulse which includes a pseudo random delay (range hop) and a pseudo random phase (direction).

2-d range hopping spread spectrum encoder/decoder system for RF tags

A method of communicating to a RF tag having a low power mode and a scan mode with a radar and an interrogator. The method comprises the steps of alternating the RF tag between the low power mode and the scan mode and then transmitting a wake-up call to the RF tag with the radar. Next, the wake-up call is received from the radar by the RF tag when the RF tag is in the scan mode. Once the wake-up call has been received, the radar will transmit a downlink message to the RF tag. Upon receipt of the downlink message, the RF tag will send an uplinked message to the radar. After the uplink message has been sent to the radar, the RF tag will return to the low power mode. By alternating the RF tag between the low power mode and the scan mode, the power consumption of the RF tag is greatly reduced thereby increasing the battery life thereof.

Tag communication protocol & system

A search radar including the improvement of apparatus for enhancing the estimation of the target angle within a search scan of the radar is disclosed. More specifically, the improvement apparatus utilizes the generated scan angles and target amplitude measurements correspondingly associated therewith to generate intermediate signals which are representative of the natural logarithm of the target amplitude measurements plus the square of the corresponding scan angle multiplied by a predetermined constant. For each search scan, the apparatus computes separately signals representative of the moments of: the scan angles, the squares of the scan angles, the products of the scan angles and corresponding intermediate signals, and the intermediate signals. In turn, the apparatus operates on the computed moment representative signals in some prespecified mathematical relationship to effect an optimum estimation for the target angle in each search scan of the radar. Simulated test results of the operation of the disclosed apparatus indicate an improvement over the simple centroid method of target angle estimation especially under the adverse conditions of a scintillating target with Rayleigh amplitude distribution.

Target angle estimator for search radars

A method and apparatus for controlling a radar beam emitted by a radar sym. The invention produces improved high resolution ground mapping by aligning the antenna isogain or isonull lines with the ground radial lines. The antenna axis is rolled by an angle determined from the geometric principles of the unit vectors along the ground radial lines. A new azimuth pointing angle is then computed and implemented. A new azimuth beamshape, azimuth beamwidth and azimuth beam spoiling factor are also computed and implemented.

Alignment and beam spreading for ground radial airborne radar

A wideband radar apparatus is provided having improved interference suppression characteristics. The known time versus bandwidth characteristic of the transmitted pulse is utilized to effect intermediate frequency bandwidth reduction in received swath echo signals. During the interpulse period, basebanded swath echo signals are then subjected to a series of adaptive interference suppressing updates. The adaptive weight vector produced during each of these updates is then applied to the same data used to generate the weights. Preferably, adaptive weight generation is performed in a systolic array according to a QR decomposition algorithm.

Wideband radar system utilizing adaptive interference canceler

The present invention is a system that performs code compression in stages where each stage includes two processing paths 36 and 38. The two paths allow bidirectional crossover cascade complementary code compression reducing the number processing stages to log.sub.2 N and reducing the number of processing by a factor of N/(2 log.sub.2 N) where N is the length of the code. Each path includes a delay provided by a delay unit 44 and each path arithmetically combines the data from its own path with data from the other path. The upper path 36 uses an adder 40 while the lower path uses an adder/substracter unit 42 which adds or subtracts depending on the phase of the transmitted complementary phase code. The delay provided in each stage increases in a binary progression with the delay of the last stage being N/2. A systolic processor 68 is the preferred embodiment although the invention could be implemented in a programmable digital signal processor. The system can also be programmed to generate codes of various lengths.

Cascaded complementary phase code compressor

A pulse compression signal processor suitable for use in a phase-coded, pulse compression radar for decoding the phase coded radar return pulses to enhance the resolvability of objects in range is disclosed. The pulse compression signal processor includes a conventional correlation processor operative in accordance with an initial filter function to convert a signal representative of the phase-code of the transmittal RF pulse to effect the range correlation response thereof. The resulting range correlation response is modified in accordance with a desired range correlation response. Both the phase code representative signal and the desired range correlation response signal are converted by fast Fourier transformations into their corresponding frequency domain signals which are divided to effect a desired filter function signal for use in decoding the phase-coded radar return pulses to effect substantially the desired range correlation response thereof. The pulse compression signal processor further includes an interative process to truncate the desired filter function signal in time in accordance with pre-established criteria.

Pulse compression radar signal processor

A system for adjusting the sidelobe response of a main antenna is disclosed. This iterative process results permits the sidelobe canceling in sequential step reduction in interference thereby greatly reducing the time required to respond to changes in the characteristics of the interference. The response of the phased array is adjusted by combining the composite signal from the main antenna with signals from auxiliary channels which have an adjustable phase and amplitude. The desired amplitude and phase of the auxiliary channels is determined using an iterative mathematical process which emphasizes the most recent data. Emphasizing the most recent data permits the system to be used in the scanning mode or to reduce interference from moving sources.

Hybrid adaptive sidelobe canceling system

A nonlinear amplitude detector generates signal amplitude from the signal's inphase and quadrature components based on a Binomial series expansion. The amplitude detector significantly reduces the processing requirement from an ideal square root operation and yet provides much improved error performance over a conventionally used linear amplitude detector. In operation, the inphase and quadrature signal components are compared for relative magnitude and the smaller magnitude signal component is squared and divided by the large magnitude signal component. The quotient from this operation is multiplied by a coefficient that is selected to provide desired amplitude error deviation characteristics. Signal amplitude is then determined by summing this product with the larger magnitude signal component.

Nonlinear amplitude detector

A synthetic aperture radar antenna, which is mechanically scanned through the squint mode, is operated to a selected roll angle to optimize the alignment of the antenna beam axis or isogain line, and the line of constant doppler frequency or isodop line. The roll angle is selected as a function of the angular position of the antenna in azimuth and elevation.

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Ellicott City, MD, United States of America

Henry E Lee