Abstract: A modulation signal generating section produces a modulation signal for controlling an oscillation frequency of a voltage-controlled oscillator. The modulation signal generating section comprises a triangular wave oscillator producing a linear modulation component of a triangular waveform which varies the modulation frequency linearly, a sine wave oscillator producing a cyclic modulation component of a sine waveform which varies the modulation frequency cyclically, and a signal adder producing the modulation signal by adding the linear modulation component and the cyclic modulation component. A transmitting signal frequency modulated by the modulation signal is mixed with a received signal and produces a beat signal comprising a fundamental wave component of a beat frequency and harmonic components.

Abstract: A system and method of processing data in a sensor system which receives signal returns from pulsed coherent transmitted signals which are transmitted at a pulse repetition rate and with a pulse repetition interval (PRI). The method includes providing range-filtered data in response to the received signal returns; formatting successive sets of data received during a post detection integration (PDI) interval into a plurality of overlapping coherent processing interval (CPI) data sequences; performing FFT processing on the overlapping CPI data sequences to provide transformed data sequences; performing range-sample CPI processing on the transformed data sequences; and performing noncoherent integration (NCI) processing on output data from the range-sample CPI processed data sequences over a range trajectory in accordance with hypothesized radar-target range rate to provide noncoherent gain-enhanced output data.

Abstract: A method of operating a SAR system comprised of emitting a sequence of pulses toward a target, alternating characteristics of pairs of successive pulses, receiving reflected pulses from the target, passing the received reflected pulses through a filter, modifying parameters of the filter in step with the transmitted pulses to match the characteristics of the successive pulses in the event a time delay between pulse transmission and reception of a pulse reflected from a target is a fraction greater than an even multiple of a pulse period, and modifying the parameters of the filter in anti-synchronism with the successive pulses in the event a time delay between pulse transmission and reception of a pulse reflected from a target is less than a fraction greater than an even multiple of a pulse period.

Abstract: The invention relates to a process for determining the deviation of the intermediate frequency from a given reference frequency (f.sub.R) in the case of a frequency-pulse radar system, characterized bythe time-related scanning of the echo signal such that, from an echo pulse of an individual target, several scanning values are obtained at different, preferably equidistant points in time within the echo pulse,the Doppler filtering by way of the thus obtained scanning values of an individual target so that several Doppler signals of the same frequency are obtained from the same target from whose phase differences the intermediate-frequency deviation is determined.

Abstract: A notched-chirp generator (20), utilizing first and second chirp generators (28, 30), a functional conversion element (40), an antichirp generator (42), a summing element (64), and a translation element (66), generates a notched-chirp signal (24). The second chirp generator (30) generates a second chirp phase signal (.phi..sub.C1), is translated by the functional conversion element (40) into an oscillating antichirp signal (A.sub.O1). The antichirp generator (42) generates an antichirp signal (A.sub.1) by scaling, weighting, and cyclically positioning the oscillating antichirp signal (A.sub.O1). The summing element (64) sums the antichirp signal (A.sub.1) with a first chirp phase signal (.phi..sub.C0), generated by the first chirp generator (28), to produce a notched-chirp phase signal (.phi..sub.N), which is converted by the translation element (66) into a notched-chirp signal (24) having a notch (26) positioned at a specific frequency (f.sub.N) determined by the antichirp signal (A.sub.

Abstract: A method of determining the velocity of a radar target wherein at least two different pulse repetition frequencies are used. Each pulse repetition frequency comprises a predetermined division into equidistant Doppler numbers. For an echo signal, a Doppler number associated with the echo signal is determined for each pulse repetition frequency. Out of two Doppler numbers associated with different pulse repetition frequencies, a nonambiguous Doppler number is subsequently determined which lies within a predetermined velocity nonambiguity range, and the velocity of the radar target is determined from this Doppler number.

Abstract: An automatic frequency control loop for maintaining a center carrier freqcy fed to a notch filter for blocking out system reverberation includes, along with the conventional elements found in an automatic frequency control loop, a control switching circuit responsive to excessive frequency deviations beyond a predetermined range as established in the AFC loop. Such excessive deviations are likely present during the time when little, if any, reverberation energy is received by a receiver carried on a moving platform, or, when signals originating from high energy level sources of countermeasure energy are being received. An interposed, selective device is included in the control switching circuit to permit operation in one of several modes as the situation demands. Including the control switching circuit in an active homing torpedo is the preferred application, although the teachings of the invention are applicable to all situations when own doppler nullification and reverberation damping is desired.

Abstract: A center-line filter for a radar receiver is a cascade of an analog filter and a digital filter. The purpose of the filter cascade is to filter out all but a single line of a pulsed spectrum. The signal is passed through the analog filter, and then over-sampled. A sharp cutoff FIR filter is used to eliminate the remaining undesired lines. Since the analog filter already has the correct matched filter characteristic in the passband, the digital filter passband is deliberately wider and unsymmetrical. After digital filtering, the filter output is decimated to provide a desired output data rate.

Abstract: A method and apparatus for locating and tracking a portable transmitter that may be deposited with currency or other items desired to be tracked, comprising a doppler antenna array, analog antenna switching, radio frequency and intermediate frequency circuitry and a digital signal processor, exhibiting increasing sensitivity, accuracy, and range.

Abstract: This invention improves the detection performance of doppler radar by censoring clutter at the output of the doppler processor, and it functions in operative association with a range CFAR. By a selective rejection of signals based on doppler characteristics and on signal amplitude, it will reduce the sum of clutter and noise at the input to the CFAR. Thus the CFAR detection threshold level is lowered, which thereby improves the detection performance for moving targets.

Abstract: A method and apparatus for identifying a remote target includes a transmitter for transmitting pulses of energy toward the target for generating echo signals, and a receiver for receiving the echo signals, and for generating received signals representing the target, noise and clutter. The received signals are applied through a plurality of cascaded channels, each including a Doppler filter cascaded with a multiplier, each also including range sidelobe suppression, for, in each of the cascaded channels, narrowband filtering the signals passing therethrough about a controllable center frequency, and for, if necessary, converting the signals passing therethrough to baseband, for thereby applying one of a plurality of Doppler filtered baseband signals to the input of each of the range sidelobe suppressors of each of the cascaded channels. The power of the Doppler filtered baseband signals in each range bin is evaluated for determining the frequency at which the spectral density is greatest.

Abstract: Improvement of radar sign-to-noise ratio and detection sensitivity in radar systems is achieved by methods employing the subtraction of the unwanted radio frequency interference, RFI, or "clone" signals thereof, from the total received signal. The Clone signals are appropriately adjusted in phase and amplitude, and are obtained from an auxilliary broad beam antenna or from a delayed sample from the system's principal antenna. When multiple RFI signals at different frequencies are present, the entire receive band is subdivided into a plurality of frequency sub-ranges.

Abstract: A large bandwidth communication system has a transmitter to transmit signals over a selectable frequency operating range and a receiver having a first mixer for mixing an LO1 signal with received transmit signals. The receiver has a first IF for processing signals received from the first mixer. A frequency synthesizer generates frequency signals for application to at least a transmit mixer in the transmitter and to at least the first mixer in the receiver.

Abstract: A radar processor is disclosed for processing the radar return samples from a Doppler radar receiver to discriminate helicopter targets from fixed-wing targets. The samples are passed through a helicopter filter which eliminates the target skin Doppler return, and passed the sidebands about the target skin return which are due to the helicopter rotor hub modulation. The coefficients of the helicopter filter are selected to maximize the signal-to-noise ratio. The radar processor requires only a few milliseconds on target for reliable detection and can, therefore, be easily implemented by scanning surveillance systems.

Abstract: Three methods are used to minimize the interference between multiple FMCW radars. The first, basic method is to use spread spectrum waveforms which differ for each radar. The FMCW waveforms have different modulation slopes for each frequency excursion. The waveforms also have different center frequencies for each excursion thus in total spreading the spectrum in frequency and modulation slope. The second method used is to control the power output for FMCW radars which have narrow beam scanning antennas, according to the azimuth position of the antenna. The third method is to select separate frequency bands for any interference which would still be above threshold. Selection would be by either infrastructure information or by comparison of "own" radar code to that received from each interfering radar over a separate, but related modulated CW transmission.

Abstract: A filtering system used in the tracking of a maneuvering target is provid A first filter estimates a partial system state at a time k in terms of target position measurements. A plurality of second filters are each provided with an acceleration model hypothesis from a prior time (k-1) free of position and velocity constraints. Each second filter generates an acceleration estimate at time k and a likelihood at time k that the acceleration model hypothesis is correct. The likelihoods from the second filters are summed to generate a probability vector at time k. A third interaction mixing filter generates the acceleration model hypotheses from prior time (k-1) using the probability vector from prior time (k-1) and the acceleration estimates from prior time (k-1). The third filter also provides an error covariance to the first filter to reflect the uncertainty in the acceleration model hypotheses from prior time (k-1).

Abstract: A radar system including a Kalman filter that processes radar return signals to produces position, velocity, acceleration, gain and residual error output signals, and a post-processor that processes these signals in accordance with a track filter bias estimation procedure. The procedure computes bias estimates and revised position, velocity and acceleration output signals that are corrected for bias error. The revised output signals are coupled to the radar system to track a target. The track filter bias estimation method computes bias estimates in accordance with the relationship: ##EQU1## where Res, K.sub.1 /K.sub.2, R and T denote the residual, gains, range, and filter cycle time, respectively, and the tilde indicates a sample averaging. The present invention also provides for improved maneuver detection by implementing an acceleration estimation algorithm used to track a maneuvering target. The present invention is applicable in all fields and areas where estimation using Kalman filters is used.

Abstract: An apparatus and method for tracking maneuvering and non-maneuvering targ in the presence of stochastic acceleration are provided. The apparatus and method utilize a two-stage Kalman estimator, the first stage of which is a bias-free filter providing target position and velocity estimates, and the second stage of which is a bias filter providing estimates of target acceleration. These two filters act together to provide parallel processing calculations thereby achieving high speed target state determination. During target maneuvers, the output of the second stage is used to correct the output of the first stage. In the absence of maneuver, the second stage is turned off and the first stage provides the target position and velocity estimates.

Abstract: A maximum likelihood estimator and range-only-initialization target detection method employed to detect and resolve targets in a multislope linear frequency modulated waveform radar. The method resolves a large number of target returns without a large amount of signal processing and without creating a significant number of false alarms, or ghosts. The method simultaneously estimates range and doppler for each target. The method rejects undesired long-range targets that fold into target regions, and processes target regions of interest around a nearest target to reduce signal processing throughput requirements. Using a K out of N detection rule, the method detects targets that compete with mainlobe rain clutter, mainlobe ground clutter, and receiver leakage. The method simultaneously estimates target parameters and optimally resolves any number of targets.

Abstract: A Doppler control circuit for a CW or pulse Doppler radar system for monitoring not only the phase shift between echo signals from several targets but also the amplitude difference between the several targets and to further tune the radar to a particular target among one or more targets from which echo signals return. The control circuit can be used in state of the art CW or pulse Doppler type radar systems. In a further system, a special circuit is provided for conditioning selected portions of the Doppler frequency spectrum to attenuate or de-emphasize portions of the echo signal corresponding to selected targets in the radar system environment, such as rain or stationary wayside objects, in order to give such echo signals less weight in determining roadway hazards.

Abstract: A Doppler control circuit for a CW or pulse Doppler radar system for monitoring not only the phase shift between echo signals from several targets but also the amplitude difference between the several targets and to further tune the radar to a particular target among one or more targets from which echo signals return. The control circuit can be used in state of the art CW or pulse Doppler type radar systems. In a further system, a continuously generated radar signal is repeatedly transmitted at different frequencies in time division fashion to define a succession of transmit and receive frames. The receive frames are divided into a plurality of time interval windows with selected windows being used to detect received signals at the different frequencies. The remaining windows can be used for subsystems of the radar system.

Abstract: Sea clutter can be removed from radar signals by accurately determining sea velocity in a coverage area of a radar scan, updating a median value for the coverage area, and selecting a clutter rejection filter for the coverage area biased on the median value for the coverage area. Preferably, a median sea velocity is stored for each coverage area, as the median value. When processing begins for a coverage area, a previously stored median sea velocity is retrieved and updated. The median sea velocity is updated by converting the median sea velocity into a median phase difference between two echo signals, based upon carrier frequency and the time between receipt of two echo signals, which is preferably more than one interpulse period. The difference in phase between the two echo signals is compared with the median phase difference and the median sea velocity is increased if the median phase difference is smaller and decreased if the median phase difference is larger.

Abstract: A multipurpose system provides radar surveillance for air traffic control purposes. The system includes four separate active phased-array antennas, each with .+-.45.degree. coverage in azimuth, from 0.degree. to 60.degree. in elevation. Each antenna element of each phased-array antenna is coupled by a low-loss path to the solid-state amplifier associated with a transmit-receive (TR) module. Each antenna produces a sequenc of pencil beams, which requires less transmitted power from the TR modules than a fan beam, but requires more time beacuse the pencil beam must be sequenced to cover the same volume as the fan beam. In order to scan the volume in a short time, the PRF is responsive to the elevation angle of the beam, so higher elevation angles use a higher PRF. Low elevation angle beams receive long transmitter pulses for high power, and pulse compression is used to restore range resolution, but the long pulse results in a large minimum range within which targets cannot be detected.

Abstract: A range tracking technique for producing a ground return signal in an FMCW radar system. The radar system produces an IF signal having frequencies within a range extent band, the IF signal including a ground return component having frequencies in a narrower ground return band. The range tracker includes a tracking system, a search system, and a controller. The tracking system receives the IF signal and a track control signal, and bandpass filters the IF signal to produce the ground return signal. The search system also receives the IF signal, together with a search control signal from the controller. The search system includes a second bandpass filter for bandpass filtering the IF signal to produce a band power signal. The controller receives and stores samples of the band power signal, and identifies the ground return component. The location of the ground return is used to adjust the track control signal, to keep the first passband centered on the ground return.

Abstract: A radar receiver and, more particularly, a radar receiver of the type which is utilized in connection with a frequency-modulated, continuous-signal radar apparatus. The radar receiver, in the receiving channel thereof, is provided with a high-pass filter of the second order which is only operated in the linear characteristic curves range, thus acting as an R.sup.4 -filter and which is connected in front of a demodulating rectifier, or in essence, an analog-digital quantitizer.

Abstract: Radar apparatus for processing a received signal having a carrier frequency f.sub.0 includes means for directing the received signal in parallel into first and second channels. A first filter in the first channel bandpass filters the received signal and is centered at a frequency f.sub.1 equal to f.sub.0 +.DELTA..sub.1 f. The first filter provides an output signal having a central frequency f.sub.0 +.DELTA..sub.1 f/2. A second filter coupled in the second channel bandpass filters the received signal and is centered at f.sub.2 =f.sub.0 +.DELTA..sub.2 f. The second filter thus provides an output signal having a central frequency f.sub.0 +.DELTA..sub.2 f/2. A first mixer in the first channel mixes the first filter output with a signal f.sub.1 =f.sub.0 +.DELTA..sub.1 f/2 to extract the carrier frequency of the first channel. Likewise, a second mixer in the second channel mixes the second filter output signal with a signal f.sub.2 =f.sub.0 +.DELTA..sub.

Abstract: In a process and device for the angular discrimination of targets by airborne radar, the angular position of a point on the ground is ascertained as a function of the Doppler frequency of an echo signal relating to the point under consideration, as determined by passband filtering the echo signals.The Doppler frequencies are selected by a bank of filters and an angular determination is made by analyzing signals including a signal representing the position in the bank of that filter selecting the Doppler frequency of the echo signal, and a reference frequency subject to closed loop control and representing the true Doppler frequency of the ground. Means are provided for maintaining data relating to the position and the range of the target constant during the process of analysis.

Abstract: A signal processing system in a transmitter/receiver system for reducing undesired amplitude, frequency and/or phase distortions arising due to variations from transmitter pulse to transmitter pulse. A plurality of sequential samples of transmitted pulses are averaged and a plurality of filter coefficients are determined therefrom. The coefficients are used in a plurality of filters which respond to a plurality of sequential samples of received pulses, the filters providing output signals in which such distortions are reduced.

Abstract: A signal acquisition circuit for a missile guidance system has a phase lock loop which is responsive to incoming signals received from a target and will lock on to the frequency of the received signal. The bandwidth of the phase lock loop is altered in dependence on the signal being received in order to distinguish between a valid target and noise.

Abstract: An arrangement for selecting between different doppler filter pairs having response characteristics optimized for ground clutter or moving rain clutter rejection. The selecting process detects the amplitude and mean doppler of the received radar echoes. The filter which is optimized for rain clutter rejection is normally used until clutter amplitude is detected above a predetermined value and the mean doppler is detected as being equal to or near zero. When such a detection is made, the filter optimized for ground clutter rejection is selected. Portions of the selecting device allow for the selection to be determined over several samples rather than switching the filters in each sample or coherent processing interval. Another portion of the circuitry changes the predetermined values which must be exceeded for a selection of the ground clutter filter, thereby preventing another filter change with only a small change in detected amplitude or mean doppler.