USA As Represented by Secretary of the Navy

The United States of America

Other

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

William M Waters

George J Linde

Bobby R Jarrett

Clifford L Temes

This invention is a communication system utilizing sharply bandlimited waveforms for sampled data communications computed for each sample value in a sequence of data samples. The computed waveform is centered at a sample point, weighted by a corresponding data value, and truncated outside an appropriate time interval. Sampled digital data in a sequence of data samples is received by a computer and scaled according to the value r(t ). A waveform generator, controlled by a computer, generates a sharply bandlimited keying waveform for each data sample and weights each waveform with the data and forms the sum of weighted waveforms to form the output signal in digital form which is converted to analog form. The analog output of the waveform generator is passed through a low-pass filter to filter out any harmonics generated, up-converted to produce a desired carrier frequency which can then be multiplexed, if required, and output as radio frequency (RF) energy which can be received by any standard receiver.

Communications system using a sharply bandlimited keying waveform

The stripline-slotline digital phase shifter is located between a ground plane associated with a patch antenna and another ground plane associated with the other patch antenna, or other output circuits. It is comprised of a section of stripline adjacent to a slot in ground plane associated with the receiving patch antenna which transitions an input electromagnetic signal to a plurality of oval slotlines, called bit circuits, of varying lengths which form a delay circuit by shifting the phase of the input electromagnetic signal. The varying lengths of slotline are switched into and out of the circuit to provide a predetermined amount of delay and the phase adjusted electromagnetic signal is transitioned to portion of stripline adjacent to a slot associated with the transmission patch antenna or other output circuits.

Selectable path stripline/slotline digital phase shifter

A waveform generator is provided for generating a high frequency waveform. A pulse generator provides a pulse train at a low frequency. A pulse converter converts the pulse train into an alternatingly positive and negative groups of pulses. A bandpass filter passes the alternatingly positive and negative groups of pulses in a frequency band centered at the high frequency to output the generated waveform at the high frequency. When the groups of pulses are a pair of pulses, a sine wave is output from the bandpass filter. A pulse delay circuit can be used to variably delay the pulse train and thereby cause a phase change in the generated waveform.

Variable phase sine wave generator for active phased arrays

A phase shifter for shifting the phase of directly sampled bandpass signals ithout having to convert to complex (I,Q) form is disclosed. An application requiring a plurality of appropriately phase shifted signals is a phased array antenna. In the operation of an exemplary phase shifter, a sequence of directly sampled data is passed into an exemplary three-stage storage unit to sequentially store r.sub.n+1, r.sub.n and r.sub.n-1 data samples. The r.sub.n sample is multiplied by cos .phi. to develop an r.sub.n cos .phi. signal, where .phi. is the desired phase shift angle. At the same time, the r.sub.n+1 and r.sub.n-1 data samples are subtracted from each other and the result is multiplied by w.sub.1 sin .phi. to develop the value w.sub.1 (r.sub.n+1 -r.sub.n-1)sin .phi.. This value is added to r.sub.n cos .phi. to produce an estimated sample value r.sub.n ', which is approximately equivalent to data directly sampled from a signal phase-shifted by .phi..

Phase shifter for directly sampled bandpass signals

A transmit/receive layer is provided adjacent to an array of antenna elements. The transmit/receive layer has an array of transmit receive modules, each module associated with one of the antenna elements. An analog to digital converter and a digital to optical converter of one of the modules couple an RF signal from the associated antenna element to optical fibers. An optical to RF converter in each of the modules converts an amplitude modulated optical transmit signal from an optical fiber to an RF transmit signal for transmission by the associated antenna element. Frequency down and up converters can be added to perform super heterodyne frequency conversion based on a reference frequency control signal transmitted over the optical fibers. At the ends of the optical fibers opposite to the transmit/receive layer, a receive layer, a transmit layer, transmit and receive beamforming layers, dedicated signal synthesizer, control signals, and amplitude modulated optical diode lasers and photodiodes are provided. The transmit layer provides an array of amplitude modulated laser diodes, each associated with one of the antenna elements. The receive layer provides an array of receive optical to digital converters coupled to the optical fibers. A matrix of switches selects appropriate signals from the M.times.N array of parallel receiving beams for subsequent radar target surveillance, tracking, and identification processing.

Layered parallel interface for an active antenna array

A millimeter wave imaging system receives millimeter wave radiation and provides video imaging signals based thereon. The system comprises an imaging lens for receiving incoming radiation; a focal plane antenna array disposed at the focal plane of the lens on which radiation received by the lens is focussed; and signal processing and display circuitry for processing the output of the antenna array and for producing and displaying corresponding video imaging signals. The focal plane antenna array comprises a planar array of a plurality of conical horns and circular waveguides which, in use, are disposed at the focal plane of the lens; and a microstrip detector assembly coupled to the waveguides for detecting the radiation received thereby. The microstrip detector assembly comprises a dielectric substrate having a plurality of microstrip conductors embedded therein, each microstrip conductor being coupled to a respective one of the waveguides, and a diode detector being connected to each microstrip conductor. A solid state commutator samples the output of the detectors and provides a resultant video imaging control signal.

Focal plane antenna array for millimeter waves

A communications system which decreases noise errors and increases informon rate without sacrificing bandwidth is formed by a transmitter and a receiver designed to handle long pulse compression wavforms. An encoder connected to the transmitter converts a voice message into digitized voice words, encodes the digitized voice words into the time shifted code sequences, and phase modulates the long pulse compression waveform, producing a M-ary coded signal at the output of the transmitter. The receiver is connected to a decoder which includes at least one convolver for computing the correlation of received digitally coded words with independently generated time shifted code sequences, and a controller for generating a plurality of data values according to the largest correlation values, and a transducer responsive to the data values.

High data rate long pulse compression waveform communication system for

Method and apparatus for improving detection ranges of a pulsed radar sys wherein electromagnetic return signal data in range cell order is doppler filtered, digitized and stored in doppler memory channels over multiple scans of an azimuth. The digital doppler data in each doppler memory channel is scan-to-scan integrated over a predetermined number of scans to produce target displays for each possible velocity. The target displays are stored in a velocity memory, which is partitioned into velocity channels, each velocity channel corresponding to one possible velocity. A selector selects the target display having the largest total magnitude as a display signal. The scan-to-scan integrated target displays are not subject to collapsing losses since only target signals plus noise signals will be stored in the doppler memory channel corresponding to the target's velocity.

Method and apparatus for increasing a radar's range with improved

Methods for accurately measuring the range between two platforms with relative motion between them using a stable clock located on each platform. A series of pulses are sent from one platform to the other at times known to each platform by prearrangement, the arrival times measured, and statistical methods used to calculate a correction from the clocks to bring them into greater synchronization, thus allowing highly accurate determination of the range between the two platforms.

Method and apparatus for precision ranging using stable clocks

This invention reduces the weight and bulk of shipboard-mounted microwave antenna systems by achieving horizontally and vertically polarized radar return signals without the need for a rotary joint.

Two-beam scanning antenna requiring no rotary joints

An Inverse Synthetic Aperture Radar (ISAR) imaging system provides an image of an incoming aircraft for the purpose of deciding which retaliatory tactic, if any, will be employed. By estimating change rates in attitude about one or more of the roll, pitch, and yaw axes, for an aircraft on a course toward the search radar, estimates of rate of change provide information from which a reliable ISAR image may be prepared. A more identifiable target and relief from ambiguity about the apparent intentions of the incoming aircraft are the result.

Aircraft attitude rate estimating device

A beam scanning antenna system that uses a small, rapidly rotatable feed enna to illuminate a large, fixed secondary collimating device, such as a reflector or electromagnetic lens, which in turn illuminates a large, fixed primary collimating device. The primary collimating device forms a narrow collimating beam that is reflected or transmitted into space. Rotation of the small feed antenna causes the beam to scan.

Fixed aperture, rotating feed, beam scanning antenna system

A dual scan rate radar system (DSR) including a phased array antenna, a tsmitter, a receiver and a control unit. Each rf pulse from the transmitter includes contiguous long-range and short-range pulses. The control unit adjusts the antenna so that the long-range pulse is transmitted into a slow beam at .theta..sub.S and the short-range pulse is transmitted into a fast beam at .theta..sub.F. The control unit also adjusts the antenna to receive the short-range pulse echos during a first part of the interpulse interval and the long-range pulse echos during a second part of the interpulse interval. The angles .theta..sub.S and .theta..sub.F are varied so that the slow and fast beam are scanned at dual rates R.sub.S and R.sub.F, respectively, where R.sub.S &lt;R.sub.F.

Dual scan rate radar

A digital coherent detector for sampling a band-limited IF signal directly o obtain its in-phase and quadrature coefficients I(t) and Q(t) without using quadrature channels comprising:

Digital coherent detector

A method for synchronizing a master clock and a remote slave clock which nominally has the same pulse frequency but may be out of time-phase comprising transmitting a master pulse to the slave, measuring the time delay, .DELTA..tau., between the received pulse and the nearest succeeding (in time) slave pulse, delaying the latter slave pulse by .DELTA..tau. to provide a conjugate slave pulse, transmitting the conjugate pulse to the master station and measuring the time difference .DELTA. between time of reception of the conjugate pulse and time of generation of the original master pulse. The time .DELTA. is equal to twice the error between the master and slave pulses. The process can also be done at the slave station if the slave pulse is transmitted to the master and a conjugate-phase master pulse is retransmitted to the slave where the measurement is accomplished. The phase of the slave pulse can then be adjusted by .DELTA./2 to synchronize it with the master pulse.

Growing community of inventors

Millersville, MD, United States of America

William M Waters