Using range and Doppler information to produce radar images is a technique used in such diverse fields as air-to-ground imaging of objects, terrain, and oceans and ground-to-air imaging of aircraft, space objects, and planets. A review of the range-Doppler technique is presented along with a description of radar imaging forms including details of data acquisition and processing techniques.

Developments in Radar Imaging

A repeater and associated method of use includes at least one antenna element for communicating in one direction and at least one antenna element for communicating in another direction. A radio frequency uplink path and a radio frequency downlink path are coupled between the antennas. At least one of the radio frequency uplink path or the radio frequency downlink path includes an adaptive cancellation circuit. The adaptive cancellation circuit is configured to generate a cancellation signal without requiring an injected signal. The cancellation signal, when added to a radio frequency signal in the respective uplink and downlink paths, substantially reduces feedback signals present in the radio frequency signal.

Repeaters for wireless communication systems

Progress in synthetic-aperture radar, (SAR) calibration is reviewed. The difficulties of calibrating both airborne and spaceborne SAR image data are addressed. The quantities measured by a SAR, i.e. radar backscatter, are defined and mathematical formulations for the three basic types of SAR image are developed. The difficulties in establishing science requirements for calibration are discussed. The measurement of SAR image quality is briefly addressed. The problem of radiometric calibration is introduced via the SAR form of the radar equation, with both internal and external calibration approaches considered. The development of algorithms for polarimetric radar calibration is reviewed and the problems involved in phase calibration of interferometric SAR are discussed. Future challenges in the field of SAR calibration are considered. >

SAR calibration: an overview

A synthetic aperture radar (SAR) can produce high-resolution two-dimensional images of mapped areas. The SAR comprises a pulsed transmitter, an antenna, and a phase-coherent receiver. The SAR is borne by a constant velocity vehicle such as an aircraft or satellite, with the antenna beam axis oriented obliquely to the velocity vector. The image plane is defined by the velocity vector and antenna beam axis. The image orthogonal coordinates are range and cross range (azimuth). The amplitude and phase of the received signals are collected for the duration of an integration time after which the signal is processed. High range resolution is achieved by the use of wide bandwidth transmitted pulses. High azimuth resolution is achieved by focusing, with a signal processing technique, an extremely long antenna that is synthesized from the coherent phase history. The pulse repetition frequency of the SAR is constrained within bounds established by the geometry and signal ambiguity limits. SAR operation requires relative motion between radar and target. Nominal velocity values are assumed for signal processing and measurable deviations are used for error compensation. Residual uncertainties and high-order derivatives of the velocity which are difficult to compensate may cause image smearing, defocusing, and increased image sidelobes. The SAR transforms the ocean surface into numerous small cells, each with dimensions of range and azimuth resolution. An image of a cell can be produced provided the radar cross section of the cell is sufficiently large and the cell phase history is deterministic. Ocean waves evidently move sufficiently uniformly to produce SAR images which correlate well with optical photographs and visual observations. The relationship between SAR images and oceanic physical features is not completely understood, and more analyses and investigations are desired.

Tutorial review of synthetic-aperture radar (SAR) with applications to imaging of the ocean surface

Non-volatile memory cells store a level of charge corresponding to the data being stored in a dielectric material storage element that is sandwiched between a control gate and the semiconductor substrate surface over channel regions of the memory cells. More than two memory states are provided by one of more than two levels of charge being stored in a common region of the dielectric material. More than one such common region may be included in each cell. In one form, two such regions are provided adjacent source and drain diffusions in a cell that also includes a select transistor positioned between them. In another form, NAND arrays of strings of memory cells store charge in regions of a dielectric layer sandwiched between word lines and the semiconductor substrate.

Multi-state non-volatile integrated circuit memory systems that employ dielectric storage elements

A method of correcting for focus errors or higher order errors, or various combinations thereof, in the final image effected by the processing of a radar. With regard to correcting focus errors, the method coherently combines the signal focus data from selected target time histories derived by a first stage processor of the radar to form a complex signal representative of the average focus error of the radar image. From the phase of the complex signal is derived a set of focus error compensation signals which are used to compensate for focus errors in the target time histories derived by the first stage processor. With regard to the higher order error correction, the method coherently combines the signal data from selected target time histories derived by the first stage processor by shifting the phase and frequency centroids of each complex signal thereof to a common value. Light filtering may be provided to remove wide band noise with a linear phase filter. Accordingly, the coherently combined and filtered error correction signals are point wise inverted and thereafter used to correct the complex signals of the time histories derived by the first stage processor. An additional embodiment is provided to permit both the focus error and higher order error correction methods to be performed at an intermediate stage in the radar processing.

Method of correcting for errors in radar imaging

A method and apparatus for providing motion compensation that allows dynamically changing flight paths during high resolution, squinted, synthetic aperture mapping by making use of a second order motion compensation by means of a two-stage correlator configuration utilizing digital signal processing techniques.

Second order motion compensator for high resolution radar

A digital processing approach has been devised for performing motion compensation in a high-resolution airborne synthetic aperture radar in the presence of simultaneous longitudinal (speed change), lateral (turn), and vertical (climb or dive) maneuvers. Both side-look and squint are accommodated in a unified scheme, which is validated by various simulation runs reported herein. Present attention is focused on theoretical verification, irrespective of mechanization or specific parameter values.

Synthetic Aperture Imaging with Maneuvers

A method of processing doppler signal data to provide time and frequency (therefore phase) coincidence for complementary code pairs of a coherent, pulse compression radar using a weighting of every other echo pulse of a particular range cell to guarantee pulse compression sidelobe cancellation in accordance with complementary code theory.

Method of reducing side lobes of complementary coded pulses in a coherent pulse compression doppler radar receiving system

A programmable analog transversal filter is disclosed for processing analog signals and comprising a charge-coupled device (CCD) for receiving a series of discrete analog signals to be delayed by increasing periods and applied to the outputs of the CCD, and a plurality of MNOS memory devices coupled to the taps of the CCD and programmed so that the output of a CCD tap is multiplied by a particular factor. In turn, the outputs of the MNOS memory devices are summed to provide an output signal ##EQU1## where W k is the weighting factor associated the k th MNOS memory device. The weighting factors are set into the system by varying the threshold voltage of the corresponding MNOS device. Positive and negative weighting factors are implemented by using first and second MNOS memory elements for each tap of the CCD, whereby depending upon the program incorporated into the system, one of the first and second MNOS memory devices is programmed to give either a positive weighting factor and the other MNOS memory device a negative weighting factor. Further, a reiterative method of setting the weights into the MNOS memory device is used to compare the system output indicative of the weighting factor as set into the MNOS memory devices, with the desired weighting factor as stored in a suitable storage memory such as a ROM, whereby a correction signal is developed to adjust the threshold voltage V Th of the MNOS memory device in accordance with the stored weighting factor. In one illustrative embodiment, the weighting factors are set in accordance with sinusoidal signals, whereby the system performs a filtering function to provide an output upon receipt of an input signal of desired frequency. In addition, the MNOS devices are reprogrammable, thus permitting a single such system to be used in many different applications. In this regard, this system is particularly adapted for complex signal processing including filtering, generating desired functions, synthetic aperture radar signal processing and target identification processing.

James H. Mims

Papers

Method of correcting for errors in radar imaging

Second order motion compensator for high resolution radar

Synthetic Aperture Imaging with Maneuvers

Method of reducing side lobes of complementary coded pulses in a coherent pulse compression doppler radar receiving system

Programmable analog transversal filter