USA as Represented by Secretary of the Navy

Other

Ben H Cantrell

Bernard L Lewis

William B Gordon

Ching Tai-Lin

Gerard V Trunk

In conventional phased array antennas, multiple signals that perform different functions, such as radar, electronic warfare (EW) and telecommunications, can each be simultaneously transmitted only through a different sub-aperture of the array. For maximum power and efficiency in conventional phased array antennas, the power amplifiers operate on one signal at a time. The present invention forms a common waveform from multiple signals for transmission through a common aperture of a phased array antenna. In wideband operations, waveform-shaping and amplitude-to-phase-modulation are used to transmit high-power diverse waveforms through every element of the array.

System for simultaneously transmitting multiple signals through each element of a radar array

The digital coherent radar generates its transmitted waveform from a low intermediate frequency (IF) and a local oscillator (LO) by digitally generated waveforms after passing through digital-to-analog (D/A) converters. The LO is increased in frequency using a product multiplier. The IF representation of the transmitted waveform is upconverted using the LO. The transmitted waveform is amplified and passed through a circulator to an antenna. The echos are received through the antenna and passed through the circulator and receiver protector. The received signal is then downconverted to a digital signal and passed on to a processor. Finally, the waveform is reset and restarted by the local oscillator generator, the digital-to-analog converters, and the analog-to-digital converter at the beginning of each pulse. It must be insured that all pulses in a pulse train are identical even though there are deterministic errors in the representation of the transmitted signals desired coherent component. This insures that all transmitted and received signals regardless of their errors in representation (i.e., spurious signal content) have the same exact representation from pulse-to-pulse for clutter like signals. If this is not done, the error type echo signals (i.e., spurious signals) will not be the same every pulse and may not cancel while the intended signal will.

Digital coherent radar

A radar interference circuit which rejects both continuous noise and shorulse interference signals. A plurality of omni-directional antennas are placed around the main directional radar antenna and connected in differing sets to a plurality of canceller means to each of which the main antenna signal is also connected. The canceller means for each set of three Omnis and the main antenna cancels out the white-noise interference received by that group of antennas. The outputs of the plurality of canceller means are then taken in different sets of two each, subtracted and compared to a threshold signal. If one or more comparator outputs are above the threshold, signifying that the antenna pulse signal is being received through the sidelobes of the antenna patterns, the outputs of these comparators will be a one signal and the OR gate, to which the comparator outputs are fed, will provide an output to blank the radar. Thus, short-pulse signals arriving through the sidelobes of the antenna patterns are rejected as interference signals.

Method and means for short pulse interference rejection

A pulse-compression, MTI, doppler-radar system for determining target velty information from a single, frequency-coded uncompressed target-return pulse includes a coded modulator, two pulse compressors, and a phase-comparison processor. The coded modulator generates for transmission an uncompressed pulse with the first and second halves of the pulse coded with the even and odd harmonic sidebands of a pulse repetition frequency, respectively. The first and second halves of the pulse returning from the target are pulse compressed simultaneously by the two pulse compressors. The phase comparison processor then determines the phase difference between the compressed pulses to obtain the target velocity information.

Frequency-coded monopulse MTI

A new system and technique for cancelling interference in frequency agile ceiving systems. Main and auxiliary signals are supplied to a pair of multiple loop side-lobe cancellers which are capable of being tuned to different frequencies. At the same time, under the control of a timing clock, plural frequencies are selected and multiplexed between two channels at the time of a radar pulse transmission. The side-lobe cancellers and radar are coupled to the channels such that each caneller operates at a given frequency for two consecutive pulse periods, with the radar transmitting at said given frequency during the second pulse period. By continuously cycling between the two channels, each canceller is operating at the proper frequency to cancel interference even though the radar is changeing frequency on a pulse to pulse basis.

Frequency diversity sidelobe canceller

A circuit which detects environmental sources of echos received by a pulscho system such as a radar and classifies the sources of the echo at each range resolution cell as either short-pulse interference, rain clutter or jamming, distributed land clutter, an isolated target or thermal noise. The circuit implements on the screen of a cathode ray tube a digital map of a selected echo source type by modulating the electron beam intensity with a binary digit (0 or 1) at each increment of the sweep corresponding to a range resolution cell. The circuit utilizes a pulse-to-pulse noncoherent subtraction to remove correlated echos, leaving only uncorrelated type echos. Short-pulse interference is then detected and the uncorrelated echo component is compared to thermal noise to determine if rain clutter or noise jamming is present. The threshold for either target detection or land clutter is determined from the uncorrelated echo component, and all correlated targets and land clutter are next detected. The correlated echos are separated into distributed land clutter and isolated targets by the following procedure: the isolated targets are required to have uncorrelated echos on each side of them in range. Finally, if no detection of any of these types is made, thermal noise is declared.

Environmental mapping system

A method of estimating the angles of arrival .theta.1 and .theta.2 of two closely spaced radar targets of which one target may be the virtual image of the other target. The targets are illuminated with a radar beam of wavelength WL, and the resulting echos from the targets are received at three directive antennas whose apertures are coplanar and whose phase centers are colinear and spaced a distance D apart. The received echos are converted to complex numbers S1, S2 and S3 representing the magnitude and phase of the respective echos received by the three directive antennas. If the plane of symmetry of the two targets is known, the value of a parameter WD is determined which minimizes L=.vertline.S1-WB(WD+WD*)S2+WB.sup.2 S3.vertline..sup.2, where WB=exp (j2.pi.D.theta.B/WL) and .theta.B is the known angle bisecting the angles of arrival of the two targets. If the plane of symmetry of the two targets is not known, the values of WD and WB are determined by solving for WD and WB which minimize L. The final step, in each case, is calculating the angles of arrival .theta.1 and .theta.2 from .theta.1=(WL2.pi.D)tan.sup.-1 [Im(WD.multidot.WB)/Re(WD.multidot.WB)], and .theta.2=(WL/2.pi.D)tan.sup.-1 [Im(WD*.multidot.WB)/Re(WD*.multidot.WB)].

Angle of arrival measurements for two unresolved sources

A pulse expansion and compression system, especially useful for radar ranging, comprising a pulse coder for expanding an input pulse and a pulse compressor of the matched-filter type. The coder consists of a plurality of delay stages into which the input pulse is fed, a discrete Fourier transform (DFT) circuit to which the output signals of the delay stages are fed, a time-dispersionmeans (TDM) comprising an arrangement of delay stages for differently delaying the output signals from the DFT, and a coherent summer for adding the real and imaginary parts of the signals from the TDM. The summer output is fed to a phase modulator and then to the transmitter. The echo signals are conjugated, time-inverted, and passed through the same DFT as the input pulse signal. The outputs of the DFT are then passed through a TDM of the same type as the first TDM, but this time in time-inverted order. The outputs of the second TDM are fed through a coherent summer and an envelope detector to provide a cross-correlated facsimile of the original input pulse.

High-speed digital pulse compressor

Multipath signals are eliminated at all but the lowest elevation angles awing monopulse techniques to be used to determine target height and azimuth in a two-dimensional, fan-beam, search-radar system. A narrow-azimuth fan beam is oriented at an angle to the vertical plane and has its boresight centered approximately on the horizon so that a V-beam is formed by the direct beam and the portion of the direct beam reflected from the surface (i.e., the portion that is below the horizon). The reflected beam does not interfere with the direct beam except in a multipath region near the reflecting surface. Frequency diversity or a receive-only beam in the vertical plane may be used to determine if a target is in the multipath region.

Monopulse, fan-beam, search-radar system with improved height and

A pulse-compression MTI doppler radar system includes an antenna, a transter, a coded modulator, a receiver and a display. The coded modulator is connected to the transmitter and has at least two waveform generators for coding pulses having low cross-correlation. A pulse-compression filter having at least two pulse compressors for providing pulse compressed signals is connected to the receiver. Each pulse compressor is matched autocorrelatively to a different one of the waveform generators. An MTI processor has two MTI processing channels which are responsive to the pulse-compressed signals and provide an output to the display.

High prf unambiguous range radar

A non-coherent, non-doppler, MTI radar system has its cancellation notch adened to include a selected range of target velocities. The apparatus includes a transmitter/receiver for transmitting and receiving short pulses in the nanosecond range. Also included is apparatus for generating multiple MTI responses having cancellation notches at different target velocities and multiplying the responses together to obtain a broadened cancellation notch.

Short-pulse non-coherent MTI

A new system and technique for providing multi-mode radar operation from a ingle scanning radar antenna at conventional scan rates. A single radar antenna has a plurality of feeds forming individual main-lobe beams equal in number to the number of radar modes to be utilized. Each of the beams is separated in azimuth by a fixed angle .theta., and rotate together at the scan rate of the antenna. For each angle .theta. that the antenna rotates the radar mode is changed so that the antenna feeds are cyclically multiplexed to each of the radar modes desired.

Growing community of inventors

Springfield, VA, United States of America

Ben H Cantrell