Abstract: Scaled multiple function non-linear FM waveforms are generated for use in digitally implemented low frequency radar. The non-linear FM waveforms are generated by combining a plurality of functions, each having varying characteristics, to form a single waveform which has the desirable characteristics of weighted linear FM waveforms without the undesirable attributes due to weighting. Accordingly, the use of the non-linear FM waveform results in an increase in detection range of eight percent over existing linear FM waveforms with no degradation in range resolution.

Abstract: A radar system includes a doppler/pulse compressor/range sidelobe suppressor filter bank (40), which separates received echo signals according to their frequency spectrum into doppler channels, and within each doppler channel performs pulse compression for reducing the duration of the received signals, and also performs range sidelobe suppression, for improving range resolution. It may be advantageous to perform certain types of processing in the time domain, such as determination of spectral moments for estimating velocity spread, mean closing velocity, and reflectivity of a diffuse target such as a weather phenomenon. An inverse (frequency-to-time) transform (50) is performed on the signals produced by the doppler/pulse compressor/range sidelobe suppressor filter bank (40), to produce a reconstructed version of the received signals. In these reconstructed signals, the pulses are compressed, and range sidelobes are reduced. The time-domain processing (62) is performed on the reconstructed signals.

Abstract: A pulse compression signal processor (10) for a laser radar system which utilizes substantially identical negative slope SAW matched filters (30,44) for compressing both the up and down chirps of a bi-directional echo signal (14). The signal processor (10) receives the echo (14) and splits it into two signals (16, 18) for processing by separate negative slope SAW matched filters (30, 44).

Abstract: In a noise radar a pseudo-random sequence is generated repeatedly and used to phase modulate a transmitted signal. The transmission is interrupted during a number of periods during each pseudo-random sequence which allows returns from targets to be received from the same antenna as is used for transmission during those periods of interruption. Each transmitted pulse, between successive periods of interruption, contains a different selection of successive digits of the code thus increasing the apparent randomness of the transmitted code and making detection more difficult.

Abstract: A radar system mounted on a satellite is scanned to provide surveillance of large areas such as the oceans. The transmitter oscillator generates bursts in the frequency range from about 20-250 megacycles. A receiver detects signals reflected from objects in the target area. The receiver enhances the value of recurrent components of selected time interval portions of the received signals. In one embodiment the transmitter bursts are modulated in accordance with a predetermined modulation pattern. The system determines to what extent it corresponds to the predetermined modulation pattern and then enhances the value of the recurrent components of the received signals. The enhancement is of those recurrent components having relative phases which change by substantially uniform increments.

Abstract: A pulsed Doppler radar system comprises a transmitter for generating and transmitting a pulse signal having expanded frequency bandwidth, an antenna apparatus for sending the output of the transmitter to a target and for receiving a signal which was sent by the transmitter and reflected by the target, a receiver for processing the received signal to obtain a complex video signal, a pulse compressing circuit including a pulse Doppler processor responsive to the complex video signal for detecting a relative speed of the target and a storage device for storing a reference signal which includes a compensation factor by which an influence of the Doppler effect is compensated in accordance with the speed of the target.

Abstract: Disclosed is a method for the processing of a signal received directly or indirectly from a transmitter, sending out pulses that are digitally encoded according to a transmission code of N instants; said processing comprising notably an operation of filtering that is matched with the transmitted signal and an operation of detection by the comparison of the post-filtering level of the signal with a so-called detection threshold; wherein the signal received is subjected to two processing operations A and B, the processing operation A comprising a self-correlation and the processing operation B comprising an intercorrelation with a mismatched code having a length at least equal to 3N, the function of intercorrelation of this mismatched code with the transmission code giving a major central lobe and at least N side lobes that are zero on either side of this major lobe; and wherein it is decided that there is a detection relating to one of the instants of the correlation or of the intercorrelation only if the leve

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: An AWTSS is shown to be made up of an improved synthetic aperture radar (SAR) for generating radar maps with various degrees of resolution required for navigation of an aircraft and detection of ground targets in the presence of electronic countermeasures and clutter. The SAR consists, in effect, of four frequency-agile radars sharing quadrants of a single array antenna mounted within a radome of a "four axis" gimbal with a sidelobe cancelling subarray mounted at the phase center of each quadrant. Motion sensors are also mounted on the single array antenna to provide signals for compensating for vibration and stored compensating signals are used to compensate for radome-induced errors. In addition, a signal processor is shown which is selectively operable to generate radar maps of any one of a number of desired degrees of resolution, such processor being adapted to operate in the presence of clutter or jamming signals.

Abstract: A pulse compression modified OMIR waveform s.sub.N (t) is obtained by computing the OMIR eigenfunctions .phi..sub.i, i=1, 2, . . . , .infin., for an autocorrelation function of the expected target impulse response, specifying a waveform c(t) having a desired pulse compression characteristic, and generating expansion terms ##EQU1## for various expansion indices N, until a desired waveform is obtained. The expansion coefficients c.sub.

Abstract: A radar system is disclosed which includes a transmitter which produces a long coded radar pulse. The return of the long coded radar pulse is compressed by a long pulse compression filter to produce a short coded pulse and the short coded pulse is compressed by a short pulse compression filter to produce a return pulse for processing by an existing processor designed to process return coded pulses of a particular format. The long pulse transmitter can also transmit a short coded precursor pulse, to improve radar range coverage, along with the long coded pulse by the provision of a switching bypass device which routes the short coded pulse return signal around the long pulse compression filter.

Abstract: Unique stretch and chirp waveform formats are described which allow significant simplification of radar signal generation and receive processing hardware. The new formats produce a non-zero intermediate frequency (IF) to facilitate in-phase and quadrature (I/Q) processing but allows the use of a homodyne type of receiver architecture. That architecture greatly simplifies the receiver hardware because the first local oscillator (LO) signal is simply a sample of the transmitter drive signal and no second LO is required. The non-zero IF is achieved by control of the timing and start frequency of the first LO waveform for stretch processing and timing of the transmit signal gating for chirp processing.

Abstract: A multi-pulse pulse compression radar system transmits two or more radar pulses having different frequency components having a time delay therebetween. A signal conditioning stage time and phase aligns the received signals and provides a composite radar signal having time and phase continuity throughout.

Abstract: A radar ranging system is disclosed which employs a frequency modulated and phase coded transmission signal which can have up to a 100 percent duty cycle and which performs time tracking of the radar target and does not require extreme accuracy in frequency modulation, or extreme receiving antenna to transmit antenna isolation.

Abstract: There are provided a communication system and an apparatus for modulating a communication signal into a chirp signal and executing the communication. In the system, a signal to be transmitted is input, a predetermined analog pattern signal is added to the input signal and is pulse position modulated, the modulated signal is converted into the chirp signal, and the chirp signal is output onto a transmission path. The converted chirp signal can be also converted into an optical signal and the optical signal can be also output onto the transmission path. After the analog or digital input signal was pulse position modulated, by converting the modulated signal into the chirp signal, the analog signal can be also transmitted and received as a chirp signal. Thus, the communication reliability can be assured without being influenced by disturbance noises or irrespective of a limitation of a transmission electric power of the transmission path.

Abstract: There are provided digital communicating method and apparatus for modulating digital signals into chirp signals and performing the communication. In this method, pulses indicative of digital signals of codes "1" and "0" are modulated, the modulated pulse signals are converted into chirp signals, the chirp signals are converted into the optical signals and output as transmission signals, and the digital signals are input and the pulses based thereon are generated. A wave of a predetermined frequency is multiplied by the pulses indicative of "1" and "0" of the digital signals and the modulation is executed. The communication signals can be converted into the chirp signals by the chirp conversion elements using the surface acoustic wave-dispersive delay lines having different converting characteristics by the simple construction.

Abstract: An optimization method for sidelobe suppression filters, and a filter utilizing a binary coding waveform are formulated. The method comprises expanding the frequency transfer function of an ideal sidelobe suppression filter into a polynomial series; truncating the polynomial series into a finite-termed polynomial series with unknown weighting coefficients A,B,C,D . . . , using the inverse Fourier transform to convert the finite-termed polynomial series into the corresponding pulse response in the time domain; then using the LP algorithm to minimize the output peak sidelobes to determine all the weighting coefficients A, B, C, D . . . and inserting them back to the inverse transfer function of the optimized filter.

Abstract: A satellite communication system including a central satellite communication terminal and a multiplicity of remote satellite communication terminals which communicate via a satellite, apparatus associated with each of the multiplicity of remote satellite communication terminals for transmitting a burst of information within a time slot and having a characteristic which is independent of the time slot and receiving apparatus associated with the central satellite communication terminal for acquiring the characteristic during each time slot and receiving the burst according to the time slot and according to the characteristic, whereby multiple transmissions may occur concurrently within a given frequency bandwidth.

Abstract: A method and apparatus exploiting the discovery that the crosscorrelation of constantly spaced rows of the matrices representing certain pulse codes sum to zero. In a ranging system, such as a radar, pulses are coded according to the rows of a such a matrix, transmitted sequentially and each return processed sequentially through a filter matched to one of the coded pulses. (A different preselected filter is used for each return.) The sequence of filters is chosen so that for returns for a given range interval, each filter is matched to the returning pulse, resulting in outputs from the filters representing auto-correlations of the returned pulses. These outputs are time delayed added coherently to form the compressed pulse, and annunciated as a target hit. Should the filters and returns be mismatched, as with ambiguous stationary clutter returns, the outputs of the filters are cross-correlations which, according to said discovery, sum to zero.

Abstract: A method of signal processing for use in high duty factor radars for detecting targets at ranges both shorter and longer than a minimum range defined by a transmitted pulse having a defined pulse length. A coded pulse coherent array waveform is transmitted and a return signal which is a waveform reflected off a target is received. The reflected waveform is sampled and time shifted by adding data to its beginning and end. The vector is then processed (pulse compressed) to obtain target information. Target information can now be obtained which is normally in a "blind zone", because the distance of the target from the radar is such that it appears during an interval when sampling is not done because of waveform transmission.

Abstract: A transmitting channel includes a pulse generator unit for generating frequency or phase code modulated pulses having a common centre frequency. The pulses are transformed to a transmitting frequency in the transmitting channel. An antenna, which is connected to the output of the transmitting channel, radiates the transformed frequency pulses and receives return signals. A receiver channel processes the return signals. The receiver channel includes a pulse compressor unit for compressing the return signals. Each pulse to be transmitted consists of two or more sub pulses, at least one of the sub pulses being substantially longer than at least another one of the sub pulses. Each sub pulse is coded with a different compression code. The compression code of each sub pulse having a low cross-correlation property with the compression codes of all other sub pulses, all sub pulses having the same center frequency.

Abstract: The difficulty of making Doppler shift velocity measurements in a chirp pulse echo ranging system is overcome by employing a pulse frequency compression filter, suitably a SAW compressor 45, having individual outputs 64, 65, 66, 67 respectively relating to adjacent contiguous frequency bands A, B, C, D, (FIG. 3) each having a bandwidth approximately equal to the chirp frequency swing. Signal detection and processing means 70 senses the occurrence of a compressed pulse on any of the outputs and measures the amplitudes of signals on all the outputs. A computer then computes the Doppler shift from the amplitude ratio of the sensed signals to adjacent frequency bands, determines the target velocity therefrom and uses the result also to correct the range measured by the counter 5.

Abstract: A tracking receiver is disclosed which utilizes optical processing for detecting and tracking input broadband chirp like emission signals. The tracking receiver includes a scanning local oscillator, the output signal of which is caused to be scanned in frequency. A mixer mixes the unknown input signal and the local oscillator output signal to produce an intermediate frequency (IF), frequency difference signal. The IF signal is analyzed in an optical spectrum analyzer which includes an acoustooptical modulator for modulating a beam of radiation, as a laser beam, with the intermediate frequency signal, and optical means, as a lens, for producing a spatial frequency distribution of the intermediate frequency spectrum in a Fourier plane. A photodetector array is provided in the Fourier plane for detecting the spatial spectrum.

Abstract: Certain man-made structures located in a complex background, such as railroad ties, telephone poles, and fences are detected by a flying craft, using a low powered structure resonant radar system. The radar system transmits a radar signal which includes wavelengths of the same order of magnitude as twice the spacing of the elements of the man-made structure or grating multiples thereof, and transmits them in a plurality of different directions and frequencies. Reflections of the transmitted radar are received and structural resonance backscatter is detected wherein the backscatter amplitude at the resonant frequency is much higher than that at adjacent frequencies or that of the clutter background, indicating the presence of the search-for type of structure. The bright structural resonance backscatter can then be exploted by the structure resonant radar for guidance, homing, etc.

Abstract: A laser distance gauge measures the distance and shape of a target by alternately performing (a) a Doppler shift measurement during optical scanning of the target's surface and/or motion of the target and (b) a chirp measurement with a chirp frequency laser signal. To ascertain changes in radial distance from the gauge to the target, the Doppler shift information is integrated and the result is combined with absolute distance measurements made in the chirp mode. A single CW laser, which operates single frequency, serves for both types of measurement. A computer changes the gauge from Doppler mode to chirp mode when the Doppler shift reaches a predetermined amount. When a chirp measurement of absolute distance is completed it reverts to Doppler mode.

Abstract: An optical gauge measures the shape of a target object by scanning a laser beam over it, (and/or measures the radial velocity of the target), by measuring the Doppler frequency shift of the reflected wave. The Doppler-shifted frequency is demodulated by a phase locked loop, which has a limited hold-in frequency range within which it is capable of staying locked on. With this invention, if the reflected wave's frequency gets close to exceeding the hold-in range of the phase locked loop, the gauge adjusts the drive frequency of an acoustooptical modulator that modulates the outbound target beam. This offsets the frequency of the target beam and keeps the return signal within the hold-in range of the phase locked loop.

Abstract: In an improved target detector, echo signals received from the same range range bracket on successive scans of the same angular direction are stored. Different combinations of elements from said echo signals are sampled and integrated, each combination being chosen to include elements indicative of a target moving with a particular velocity. Different combinations are indicative of different target velocities, or of targets situated at different initial ranges, and means are provided for signalling an alarm when the integral of any combination exceeds a threshold.

Abstract: A method of rapidly reacquiring a pseudonoise spread spectrum coded signal after short outages includes calculating the new positions of the moving stations relative to the old positions of the moving stations and for determining the accurate displacement and the accurate direction the platforms have moved in their new direction after a short time outage. The method includes calculating a triangle which includes the displacement between the moving stations' old position and the moving stations new position and the included angle between the direction of movement and the line of sight between said moving platforms at the time of outage. A range displacement adjustment is calculated on the basis of the triangle for each moving station and the range factor resulting from this calculation is applied to the PN generators of the receiver and transmitter in each of the moving stations to independently adjust for each station's movement.

Abstract: Stable measurement of terrain-height variations is provided by this radar system which employs a very low power spread spectrum transmitted signal which, after reception, is processed digitally for extremely stable and predictable performance. The system also includes an automatic power control circuit to maintain the transmitted power at the minimum required level.

Abstract: A pulse modulator for a radar system employing resonant charging of a pulse forming network and circuits for periodically discharging the network to form a power pulse applied to a microwave transmitter such as a magnetron, for example. The system includes circuits for controlling the pulse forming network charge effective at a time ahead of the discharging of the network, thereby to stabilize (regulate) the power pulse amplitude. The circuits shown provide for introduction of an increment of charge current independently of the resonant charging current of a magnitude determined by evaluation of the pulse forming network terminal voltage.

Abstract: A broadband receiver for converting an input radio frequency signal into output pulses includes provision for expanding the width of the output pulses (50) to permit pulse processing by conventional equipment at slower processing rates. A scanning local oscillator (42) frequency modulates the input signal to create a frequency modulated signal which is compressed into a pulse by a dispersive delay line (40). The width of the output pulse is increased by producing a mismatch or differential in the frequency versus time slopes (52, 54) of the oscillator and dispersive delay line. The slope differential is achieved by a function generator (58, 68) which maintains the frequency versus time slope of the scanning local oscillator at a value different than that produced by the dispersive delay line.

Abstract: A pulse radar apparatus is provided with a transmitter (1), a transmitting antenna (2) and a receiving antenna system (3) with a first and a second receiving channel (4 and 5) coupled thereto. The receiving antenna system (3) comprises N stacked receiving antennas (A.sub.0, A.sub.1, . . . , A.sub.N-1). The first receiving channel (4) comprises N receiving circuits (B.sub.0, B.sub.1, . . . , B.sub.N-1), each connected to a corresponding receiving antenna (A.sub.0, A.sub.1, . . . , A.sub.N-1) and each processing the particular echo signal into two orthogonally phase-detected and digitized video signal components, and a beamformer (14) to derive from said components the orthogonal components I.sub.k, Q.sub.k of the video signal determined jointly by the N receiving circuits in accordance with a receiving beam pattern k corresponding with a specific elevation interval. The second receiving channel (5) comprises N receivers (B.sub.0, B.sub.1, . . . , B.sub.

Abstract: A pulse compression signal processor suitable for use in a phase-coded, pulse compression radar for decoding the phase coded radar return pulses to enhance the resolvability of objects in range is disclosed. The pulse compression signal processor includes a conventional correlation processor operative in accordance with an initial filter function to convert a signal representative of the phase-code of the transmittal RF pulse to effect the range correlation response thereof. The resulting range correlation response is modified in accordance with a desired range correlation response. Both the phase code representative signal and the desired range correlation response signal are converted by fast Fourier transformations into their corresponding frequency domain signals which are divided to effect a desired filter function signal for use in decoding the phase-coded radar return pulses to effect substantially the desired range correlation response thereof.