The United States of America As Represented by the Administrator of the

Other

Chialin Wu

Robert A Frosch

Richard M Goldstein

Edward R Caro

Kuang Yung Liu

Vance C Tyree

A full duplex frequency division multiplex communication system which comprises a number of transceivers constituting user stations which communicate with one another over a common channel, such as a wireless link or a two-direction coaxial cable, with each transceiver operating on a single fixed intermediate frequency for transmission and reception. The system includes a network frequency converter for shifting the transmission frequency band used by the transceivers into a different receiving frequency band which does not overlap the transmission frequency band. Single sideband modulation of the intermediate frequency carrier is used, and full duplex communication is achieved by using one of the sidebands of the intermediate frequency carrier for transmission, and the other sideband for reception. Each transceiver includes a programmable frequency synthesizer for channel selection, and upper and lower sideband filters, with one of the filters being used for transmission and the other for reception.

Full duplex frequency division multiplex communication system

By using two SAR antennas spaced a known distance, B, and oriented at substantially the same look angle to illuminate the same target area, pixel data from the two antennas may be compared in phase to determine a difference .DELTA..phi. from which a slant angle .theta. is determined for each pixel point from an equation .DELTA..phi.=(2.pi.B/.lambda.)sin(.theta.-.alpha.), where .lambda. is the radar wavelength and .alpha. is the roll angle of the aircraft. The height, h, of each pixel point from the aircraft is determined from the equation h=R cos .theta., and from the known altitude, a, of the aircraft above sea level, the altitude (elevation), a', of each point is determined from the difference a-h. This elevation data may be displayed with the SAR image by, for example, quantizing the elevation at increments of 100 feet starting at sea level, and color coding pixels of the same quantized elevation. The distance, d, of each pixel from the ground track of the aircraft used for the display may be determined more accurately from the equation d=R sin .theta..

Method and apparatus for contour mapping using synthetic aperture radar

A technique for self-calibration and phasing of a lens-feed array antenna, while normal operation is stopped, utilizes reflected energy of a continuous and coherent wave broadcast by a transmitter (11) through a central feed (10) while a phase controller (21) advances the phase angles of reciprocal phase shifters (14) in radiation electronics (RE1-REN) of the array elements (1-N) at different rates to provide a distinct frequency modulation of electromagnetic wave energy returned by reflection in one mode (switch 19 closed) and leakage in another mode (switch 19 open) from the radiation electronics of each array element. The composite return signal received by a synchronous receiver (12) goes through a Fourier transform processing system (20) and produces a response function for each antenna element. Compensation of the phase angles for the antenna elements required to conform the antenna response to a precomputed array pattern is derived from the reciprocal square root of the response functions for the antenna elements which, for a rectangular array of N.times.M elements, is a response function T(n,m). A third mode of calibration uses an external pilot tone from a separate antenna element (44). Respective responses T.sub.1 (n,m), T.sub.2 (n,m) and T.sub.3 (n,m) are thus obtained from the three modes of calibration. From those, the separate responses T.sub..phi., T.sub.t and T.sub.r of the reciprocal phase shifter, radiation electronics, and synchronous receiver can be obtained by solving the following three simultaneous equations:

Method and apparatus for self-calibration and phasing of array antenna

A synthetic aperture radar system (SAR) having a range correlator (10) is provided with a hybrid azimuth correlator (12) for correlation utilizing a block-pipelined Fast Fourier Transform (12a) having a predetermined FFT transform size with delay elements (Z) for so delaying SAR range correlated data as to embed in the Fourier transform operation a corner-turning function as the range correlated SAR data is converted from the time domain to a frequency domain. A transversal filter (12b) connected to receive the SAR data in the frequency domain, and from a generator (14b) a range migration compensation function, D, to a programmable shift register (30) for accurate range migration compensation; weights, W.sub.i, to multipliers (35-38) for interpolation, and an azimuth reference function, .phi..sub.j, in the frequency domain to a multiplier 42 for correlation of the SAR data. Following the transversal filter is a block-pipelined inverse FFT (12c) used to restore azimuth correlated data in the frequency domain to the time domain for imaging. The FFT transform size is selected to accommodate the different SAR azimuth aperture lengths, number of looks and prefiltering requirements.

Pipelined digital SAR azimuth correlator using hybrid FFT/transversal

A spaceborne synthetic aperture radar having pipeline multiple-look data processing makes use of excessive azimuth bandwidth in radar echo signals to produce multiple-look images. Time multiplexed single-look image lines from an azimuth correlator go through an energy analyzer which analyzes the mean energy in each separate look to determine the radar antenna electric boresight for use in generating the correct reference functions for the production of high quality SAR images. The multiplexed single look image lines also go through a registration delay to produce multiple-look images.

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Pasadena, CA, United States of America

Chialin Wu