Abstract: A radar performs accurate and appropriate pairing even if peaks of approximately identical signal intensities or even if a plurality of peak groups having identical representative beam bearings exist in the frequency spectrum. First, the peak frequency of a peak which appears in the frequency spectrum is determined for each of an up-modulating interval and a down-modulating interval in predetermined beam bearings, and signal-intensity profiles in the beam bearings are extracted with regard to a plurality of beam portions which are adjacent to the beam bearings. Next, the correlation level between the signal-intensity profiles at the up-modulating interval and the down-modulating interval is determined, and pairing is performed in sequence starting from the profiles having a higher correlation level.

Abstract: In an FM-CW radar system, regarding peaks appearing in the frequency spectrum of a beat signal in an FM-CW radar, groups of consecutive peaks in beam bearings within a predetermined frequency difference are regarded as being caused by reflected waves from a single target, and based on a combination of a peak group in an up-modulating interval and a peak group in a down-modulating interval, a relative distance to a target and its relative speed are determined.

Abstract: A spread spectrum radar system, characterized in that the receive radar signal is mixed down to baseband and applied to leak cancellation means for subtracting therefrom an attenuated delayed version of the transmit radar signal to provide a reflected receive radar signal with improved signal-to-noise ratio for further processing and to prevent receiver saturation. The radar allows the capture of the range and speed of identified targets, and facilitates .a determination of the target's direction. It exhibits an inherent immunity to electromagnetic interference, and is relatively undetectable by radar detectors. The system is easily reprogrammable for different range resolutions and permits Doppler processing to be independent of the angle between radar signal and the track of the target.

Abstract: To suppress interfering stationary targets in radar source data, a STAP filtering method is used. Filtering coefficients are determined, and filtering of the data takes place, in the frequency domain; the process is therefore limited to a few computing operations per matrix element of the range/Doppler matrix. Since, by means of the STAP filter according to the invention, the optimal filtering characteristics can be implemented, the stationary target suppression also functions in the range of the minor lobes of the antenna. Therefore, data of individual adjacent channels (L/R, left/right) can be processed as well as summation and difference signals (&Sgr;/&Dgr;).

Abstract: In conjunction with an arrangement for the interferometric radar measurement in connection with a radar system operating according to the ROSAR principle, comprising one coherent transmitting antenna and two coherent receiving antennas and their receiving channels, in connection with which the difference in the path between the two distances of the antennas and the measured points of impact is calculated by the wavelength &lgr; of the emitted radar signal and the measured phase difference of the receiving echo of the two coherent receiving channels, it is proposed that the interferometric ROSAR system is integrated in or on a rotating device and positioned in such a way that each relevant area of the field to be measured can be detected.

Abstract: The invention is a method and apparatus for determining the locations of a plurality of actual objects based on the output of a plurality of range sensors. A multiplicity of range measurements are obtained from a plurality of sensors, each sensor capable of providing a multiplicity of range measurements. The range measurements from the plurality of sensors are correlated with each other to generate a list of potential objects and to order that list of potential objects from highest to lowest likelihood of being an actual object. The order may be based upon a cumulative error of the individual sensor measurements upon which the potential object is based. The ordered list of potential objects is then pared down to a smaller list of actual objects by assuming that the potential object highest in the ordered list as an actual object, and then removing from the list all other lower-ordered potential objects that are based on any of the range measurements upon which the selected object is based.

Abstract: First-arriving-pulse detector (FAP) circuitry includes a correlator circuitry and a threshold circuitry. The correlator circuitry correlates a received signal with a template signal to provide an output signal. The threshold circuitry provides a first-arriving-pulse signal depending on the relative values of the output signal of the correlator circuitry and a threshold signal.

Abstract: A dual channel microwave sensor employs single sideband Doppler techniques in innumerable vibration, motion, and displacement applications. When combined with an active reflector, the sensor provides accurate range and material thickness measurements even in cluttered environments. The active reflector can also be used to transmit multi-channel data to the sensor. The sensor is a homodyne pulse Doppler radar with phasing-type Doppler sideband demodulation having a 4-decade baseband frequency range. Ranging is accomplished by comparing the phase of the Doppler sidebands when phase modulated by an active reflector. The active reflector employs a switch or modulator connected to an antenna or other reflector. In one mode, the active reflector is quadrature modulated to provide SSB reflections.

Abstract: A continuous signal of a radio frequency source is connected to an antenna using at least one mixer to generate and analyze radar pulses. To generate a radar pulse, the at least one mixer is briefly placed into a state of low throughput loss. After the radar pulse is generated and transmitted, the at least one mixer is switched over to a receive mode to analyze a mixed signal formed by a receive signal, in particular at least one radar pulse reflected by an object, and the continuous signal of the radio frequency source.

Abstract: Systems and methods that may be used to determine the distance between an orbiting satellite and a ground station. A master clock divider circuit generates clock signals derived from a master clock. A transmit code generation circuit generates pseudo-random number codes and processes the pseudo-random number codes to produce a composite signal having positive and negative correlation peaks that is transmitted to the satellite as an analog signal. A digitizing circuit receives the analog signal transmitted from the satellite, and digitizes the analog signal. A frequency domain matched filter match filters the digitized analog signal to produce correlation peaks contained in the digitized analog signal.

Abstract: In a method for operating a rotating synthetic aperture radar system that works with pulse frequency or in FM-CW operation in order to detect, penetrate and evaluate objects that are located vertically below the helicopter carrying the ROSAR device, pixels are determined using their own specific doppler histories.

Abstract: A complex frequency shift keyed homodyned diplexed radar system and method that can accurately determine the range of one or more targets where the targets have little or no velocity relative to the radar system. The system and method generates a FSK electromagnetic wave that is reflected off the one or more targets and converted into a delayed or phase shifted baseband signal and undelayed baseband signal where the delayed and an undelayed baseband signal may be analyzed to determine the range of the one or more targets.

Abstract: The signal echo monitoring device includes a transmitting unit (5) for broadcasting a transmitted signal (s(t)) which is a group of randomly generated pulses, a receiving unit (6) for receiving an echo signal (e(t)), reflected by an object (12), of the transmitted signal and a combined control and evaluation unit (2) including a device (10) for jointly evaluating the transmitted signal (s(t)) and the echo signal (e(t)) with an integrated adaptive filter (14). The adaptive filter (14) automatically calibrates its impulse response b(t) and may be a digital filter.

Abstract: The invention relates to a radar distance measuring device. An especially linear frequency-modulated high frequency signal is emitted via an antenna and mixed with an echo signal reflected by a target object whose distance is to be determined. The distance of said target object can then be calculated by analyzing the frequency of the mix result. The aim of the invention is to improve the distance resolution or increase the accuracy of measurement. To this end, a first frequency analysis is first carried out to obtain a rough analysis result. Said rough analysis result is used to control a filtering device which then restricts the mix result in its time range to a segment around the frequency of the target object. A discrete Fourier transformation is then carried out for this segment in order to produce an analysis result with a more refined scanning step than the first frequency analysis.

Abstract: A random signal radar unit transmits a variable signal modulated by random noise (at 41). The return signal from the target area is correlated (at 61) with a sample of the transmitted signal, effectively compressing the spread spectrum waveform into a narrow band signal. The result is a covert high resolution radar which can be instrumented to operate in a number of single-or multi-mode configurations. By randomly varying biphase modulation (at 41, 35) and by down beating (at 49) the echo signal with the modulation delayed by a time equivalent to that of a leakage delay, a random signal is produced (at 35, 39) in which leakage return signals are readily filtered (at 53, 59).

Abstract: A random signal radar unit transmits a variable signal modulated by random noise (at 35). The return signal from the target area is correlated (at 61) with a sample of the transmitted signal, effectively compressing the spread spectrum waveform into a narrow band signal. The result is a covert high resolution radar which can be instrumented to operate in a number of single-or multi-mode configurations. By randomly varying biphase modulation (at 41, 35) and by modulating (at 49) the echo signal with the modulation delayed by a time equivalent to that of a leakage delay, a random signal is produced (at 35, 39) in which leakage return signals are readily filtered (at 53, 59).

Abstract: Provided is a radar apparatus for use on a vehicle and for detecting one target or two or more targets present in a scan range by scanning the scan range with a radar beam, which has a means for obtaining prior target data by scanning the scan range with the radar beam, a grouping means for carrying out grouping of the prior target data according to a predetermined condition to obtain group data, and a target recognition means for identifying the group data and prior target data remaining without being grouped, as detection data corresponding to respective targets and carrying out recognition of each target corresponding to each detection data. The grouping means makes provision of a plurality of predetermined conditions, selects one condition or two or more conditions according to position information of prior target data to be grouped, and carries out the grouping based on the condition(s) selected. This radar apparatus for use on the vehicle can accurately perform the grouping of point data.

Abstract: A method, and exemplary apparatus for practicing the method, is shown for operating a pulse radar to allow the radar ambiguity function of such radar to be modified by controlling the range and Doppler ambiguities due to the pulse waveform of such radar.

Abstract: A pseudo random noise code is generated synchronously with a reference clock signal. A first forward electromagnetic wave is transmitted in response to the pseudo random noise code. A first echo wave is received which is caused by reflection of the first forward electromagnetic wave at an object. The received first echo wave is converted into a binary signal. A value of a correlation between the binary signal and the pseudo random noise code is repetitively calculated at a predetermined period having a synchronous relation with the reference clock signal. A time interval taken by the first forward electromagnetic wave and the first echo wave to travel to and from the object is measured in response to a timing at which the calculated correlation value peaks. Then, a second forward electromagnetic wave is transmitted in response to a transmitted pulse signal is transmitted. A second echo wave related to the second forward electromagnetic wave is received.

Abstract: In an air traffic control radar system, a processor is described for correlating primary target data received from a target with a target report and a target track, wherein the processor has a search acquisition time that is adapted to the distance of the target from the radar site. The search acquisition time is shorter for more distant targets. The processor can employ a shorter cycle time (time quantum) to establish a correlation between target data and target reports than would otherwise be possible with conventional fixed search acquisition times. The average total dwell time may be reduced while complying with the mandated maximum processing time for more difficult radar reports.

Abstract: A random signal radar unit transmits a variable signal modulated by random noise (at 35). The return signal from the target area is correlated (at 61) with a sample of the transmitted signal, effectively compressing the spread spectrum waveform into a narrow band signal. The result is a covert high resolution radar which can be instrumented to operate in a number of single-or multi-mode configurations. By randomly varying biphase modulation (at 41, 35) and by, modulating (at 49) the echo signal with the modulation delayed by a time equivalent to that of a leakage delay, a random signal is produced (at 35, 39) in which leakage return signals are readily filtered (at 53, 59).

Abstract: A method for resolving range ambiguities and separating overlaid signals in a Doppler weather radar is proposed. For uniform PRT transmission, it consists of a special deterministic code for phases of the transmitted pulsed, and associated decoding and processing of return signals. In the decoding process when the signal from one range interval is made coherent, the signal from the other range interval has a multiple split spectrum. The multiple spectra have the same shape but are offset from each other. Processing steps to separate the overlaid signals and a procedure to estimate the spectral moments are given. One crucial aspect in this procedure is the magnitude domain deconvolution. The magnitude domain deconvolution is also applied to a staggered PRT transmission scheme whereby it enables the estimation of spectral parameters with much lower standard error than the known methods.

Abstract: An electronic distance meter comprises an integrated circuit from a GPS navigation receiver having a local pseudo-random number code generator for code demodulation that is connected to modulate either a polychromatic or a monochromatic light source. An optical system focuses the light on a distant target with an unknown range. Reflections from the distant target are focused on a light detector that produces a phase-delayed copy of the original pseudo-random number code. The time-of-flight to and back from the distant target is a function of the distance. The GPS receiver integrated circuit computes the range based on the code-phase delay to a precision better than one centimeter. The position of a remote target can be triangulated from several electronic distance meters each having known positions, e.g., determined by included GPS navigation receivers.

Abstract: A CW radar range measuring system having a transmitter adapted to transmit a continuous wave radar signal phase encoded in accordance with a code and a receiver adapted to receive a radar return from the transmitted radar signal. The receiver includes an analog to digital converter section for converting a sequence of samples of the radar return into a corresponding sequence of digital words. A digital correlator/integrator is fed by the digital words and the code for providing an indication of radar return energy as a function of range from the transmitter. A processor is fed by the digital correlator/integrator for determining, from the indicated energy, target range. The system includes a frequency spectrum analyzer for determining a frequency spectrum of the digital words and wherein the processor determines the target Doppler frequency from such determined frequency spectrum.

Abstract: A radar device transmits an electric wave whose band is spread by a PN code, receives a reflected wave of the electric wave from an object 10, detects correlation between a received signal and a PN code which is delayed, and thereby detects the object. A receiving part 18 connects three receiving antennas 16a.about.16c sequentially one by one, thereby to receive a reflected wave from an object. The three receiving antennas are arranged having their directions so staggered that their antenna beam patterns partly overlap with each other. A correlation detection circuit 19 detects such a slide width that a value of correlation between a received signal received by each of the antennas and the PN code exceeds a predetermined threshold. An operation part 12 obtains an azimuth of an object based on the detected slide width and beam pattern characteristics of the antennas.

Abstract: An object is to provide a cheap digital beamforming radar apparatus.

Abstract: The present invention describes a method and apparatus for improving the autocorrelation performance in spread spectrum radar and communications systems by using a tri-state digital correlator to demodulate the received biphase modulated waveform. The tri-state correlator (100) includes a multiplexer (112) having a code input for receiving a tri-state code sequence, and three inputs each for receiving a sequence of data words including a first input for receiving a digitized signal data word, a second input for receiving an inverted digitized signal data word, and a third input for receiving a zero data word. The multiplexer includes an output and a means for producing a sequence of data words at the output, said means presenting at the output exactly one of the three data words appearing at either the first, second, or third input depending on which of the three code states appears at the code input.

Abstract: A method for automatic group tracking detects target formations and group tracks corresponding to each formation. Pseudo-observations are formed to represent missing observations in each track group. The pseudo-observations update the track states of undetected targets. Track validity estimates eliminate false tracks resulting from series of pseudo-observations. A group average velocity applied to each track in the group helps to maintain velocity stability. The operator has the option of suppressing the display of all tracks except for the leader of each group to eliminate the distraction of intra-group switching. This method can be applied to trackers that maintain a single track for each target or to trackers that maintain multiple track branches on each target, such as MHT.

Abstract: A signal processing system applies space-time adaptive processing ("STAP") to an airborne surveillance Doppler radar comprised of a single-channel, electronically scanned antenna. The STAP substantially improves signal-to-interference-plus-noise ratio ("SINR") by synthetically creating angular degrees of freedom, thereby improving the detection of weak targets.

Abstract: A continuous wave radar altimeter comprises a pulsed power control (4), operable when the signal-to-noise ratio of the received signal is likely to be too low, to pulse the transmitted power so that the power varies between a non-zero base level and a higher level. The receiver channel (13, 14) is switched off during each transmitted pulse.

Abstract: A radar including a plurality of antenna arrays (B, . . . , J), for example linear arrays, the reception of electromagnetic waves being coherent for each antenna element in each array. The extraction of target signals from sidelobe signals according to the invention is obtained by comparing the signals received by the various arrays. A statistical processing allows to eliminate the responses corresponding to the array sidelobes. The invention is mainly applicable to radars including a plurality of linear lacunary antenna arrays with an isotropic disposition in space.

Abstract: An apparatus for measuring the height and cross-track offset of a surface location from a moving platform is defined. First and second antennas positioned on an underside of the platform are directed downwardly toward the surface. A transmitter associated with one of the antennas transmits a signal toward the surface. A first coherent detector associated with the first antenna detects a received signal corresponding to the transmitted signal as reflected by the surface and generates in-phase and quadrature components of the detected signal relative to the transmitted signal. A second coherent detector associated with the second antenna detects a received signal corresponding to the transmitted signal as reflected by the surface and generates a second set of in-phase and quadrature components of the detected signal relative to the transmitted signal. An analog to digital (A/D) converter converts the in-phase and quadrature components into digital information stored in a memory.

Abstract: A multiresolution, multirate approach for detecting and following targets. The resolution of data obtained from a target scanning region is reduced spatially and temporally in order to provide to a tracker a reduced amount of data to calculate. Balances of computer processing resources with long-range detection and multiple target tracking are provided. Computer processing resources can be allocated to other systems while still maintaining an accurate tracking function and alternatively, the tracking function can receive a high level of computer processing resources and track at a finer resolution. An ability to recover raw data points from the spatially and temporally reduced values is also provided.

Abstract: In accordance with the teachings of the present invention, a passive tracking system (30) and method of passively determining a range (R) to a remote signal emitter (10) elevated a distance above ground level (14) is provided. The method includes aligning an antenna (32) also elevated above ground level (14) substantially in the direction of the remote signal emitter (10). The antenna (32) receives combined radiated energy along a direct path (16) from the remote signal emitter (10) as well as radiated energy that has bounced off the ground level (14) and has been received along a bounce path (18) from the remote signal emitter (10). The range (R) to the remote signal emitter (10) is calculated based upon the combined direct and bounce path signals. Correlation processing and geometric triangulation is employed to calculate the range (R) to the remote signal emitter (10).

Abstract: A method and apparatus for preventing the occurrence of range ambiguities and Doppler ambiguities in both a radar and sonar environment. A series of N pulses are produced, each of which contains a number of contagious subpulses. Each of the subpulses exhibit a different frequency than the remaining subpulses in that particular pulse. Furthermore, the order of appearance of the subpulses in each of the pulses is unique with respect to the remaining pulses in the series. A matched filter receiver and Doppler processor are used to provide auto correlations and cross correlations to prevent the range ambiguities and Doppler ambiguities.

Abstract: A radio range finding system includes a radio range finder and a plurality of remote mobile transponders. The radio range finder transmits a signal modulated with an address code identifying a particular mobile transponder. When a mobile transponder receives the modulated signal M.sub.s transmitted by the radio range finder and the modulated signal has been modulated with an address code that corresponds to the address assigned to that mobile transponder, the mobile transponder transponds a return signal R.sub.s to the radio range finder. A receiver in the radio range finder conveys the received signal to a mixer which also receives an internal carrier signal identical to the modulated signal output by transmitter. The output of the mixer is then filtered and demodulated to yield an output signal proportional to the distance between the mobile transponder and the radio range finder.

Abstract: A radar apparatus provided with a transmitting unit, antenna unit and a receiver unit. The transmitting unit transmits pulses having a modulation for enabling pulse compression on reception. As an ECCM feature, the radar apparatus is further provided with a blanking circuit. The blanking circuit includes two filters, one filter being responsive to the first half of the transmitting pulse only and the other filter being responsive to the second half of the transmitting pulse only. Blanking occurs if both filters simultaneously produce an output.

Abstract: A CW radar range measuring system having a transmitter adapted to transmit a continuous wave radar signal phase encoded in accordance with a code and a receiver adapted to receive a radar return from the transmitted radar signal. The receiver includes an analog to digital converter section for converting a sequence of samples of the radar return into a corresponding sequence of digital words. A digital correlator/integrator is fed by the digital words and the code for providing an indication of radar return energy as a function of range from the transmitter. A processor is fed by the digital correlator/integrator for determining, from the indicated energy, target range. The system includes a frequency spectrum analyzer for determining a frequency spectrum of the digital words and wherein the processor determines the target Doppler frequency from such determined frequency spectrum.

Abstract: A method and apparatus for enhancing resolution of range estimates in all echo location systems and, specifically, such systems as Radar, Sonar, and Synthetic Aperture Radar (SAR), for example. The invention utilizes high order signal processing to "sharpen" or contract the main lobe of the processing system ambiguity function and suppress its side lobes, for a given transmission pulse bandwidth. The method and apparatus may be implemented in the frequency domain or time domain. Enhanced resolution is achieved by using a filter (MSC filter), according to this invention, in the echo location data processing system so that the received echo data is processed by the MSC filter to produce a signal that exhibits enhanced range resolution. The MSC filter output, H(.omega.), which is specific to the transmitted pulse waveform, is the ratio of a high-order manipulation of the transmitted signal with its modified spectral profile.

Abstract: A decimating digital PN receiver (10) processes a target return signal. The target return signal is decimated (34) processed at a slower speed. The decimated target return signal is then digitally correlated (28). The correlated signal is digitally filtered (30) and a fast Fourier transform (32) is applied to produce the output (33).

Abstract: A network of localizers determines relative locations in three-dimensional space to within 1 cm by cooperatively measuring propagation times of pseudorandom sequences of electromagnetic impulses. Ranging transmissions may include encoded digital information to increase accuracy. The propagation time is determined from a correlator circuit which provides an analog pseudo-autocorrelation function sampled at discrete time bins. The correlator has a number of integrators, each integrator providing a signal proportional to the time integral of the product of the expected pulse sequence delayed by one of the discrete time bins, and the non-delayed received antenna signal. With the impulses organized as doublets the sampled correlator output can vary considerably in shape depending on where the autocorrelation function peak falls in relation to the nearest bin. Using pattern recognition the time of arrival of the received signal can be determined to within a time much smaller than the separation between bins.

Abstract: A signal processing system applies space-time adaptive processing ("STAP") to an airborne surveillance Doppler radar comprised of a single-channel, rotating antenna. The STAP substantially improves signal-to-interference-plus-noise ratio ("SINR"), thereby improving the detection of weak targets.

Abstract: A continuous wave ranging system comprises a modulator for modulating an r.f. carrier signal in accordance with a pseudo random code, a transmitting antenna for radiating the signal towards a target, a receiving antenna and receiver for detecting the signal reflected from the target, a correlator for correlating the detected signal with the transmitted code with a selected phase shift corresponding to the current range gate to be tested, whereby the range of the target from the system may be determined, and filtering means for filtering from the output of the correlator those range gate amplitudes which vary with a frequency less than a predetermined value.

Abstract: A precision ranging radar system for use in parking and backup maneuvers by drivers of vehicles to avoid collisions. The radar system includes a noise code generator for generating a noise code, a data source for generating a data bit stream, and a local oscillator microwave source. A data mixing mechanism is coupled to the noise code generator and data source for embedding data derived from the data source into the noise code. Transmit and receive microwave antennas are provided. A transmit phase modulator is coupled to the data mixing mechanism, the local oscillator microwave source, and the transmit antenna. A receive phase modulator is coupled to the local oscillator microwave source, and a code delay unit is coupled to the noise code generator and the receive phase modulator. A downconverter mixer is coupled to the receive microwave antenna and to the receive phase modulator, and a baseband integrator and amplifier is coupled to the downconverter mixer for outputting data from the radar system.

Abstract: A radar altimeter system uses a microprocessor-based subsystem to process radar signals in software. The subsystem includes a track loop and a verify loop for digital signal processing of the radar signals. The track loop generates a gate pulse and integrates a radar return signal over the time window defined by the gate pulse in order to determine the leading edge of the return pulse. The verify loop positions the gate pulse for maximum overlap with the return pulse and integrates the return pulse over the gate pulse to determine the maximum signal strength of the radar return signal.

Abstract: A method and device of the pulse-compression radar or sonar type which makes it possible to determine the speed of a moving object is provided with a transmitter system, a receiver system, and a signal processing system. The transmitter system is capable of transmitting two associated pulses, one of which is modulated with an increasing variation law and the other of which is modulated with a decreasing variation law. The signal processing system includes two correlators, an adder, a subtractor, and a computer.

Abstract: Range-Doppler ambiguity is eliminated from an ultra-wideband radar system by transmitting an ultra-wideband chirped pulse towards a moving target, and mixing it with the doppler-shifted chirped pulse which is received as a target echo return signal. Multioctave radar tracing systems can potentiality track stealth aircraft without ambiguity since pulses containing many frequencies can defeat narrow-band radar absorbing material coatings. The unambiguous range-doppler signal processing method mixes the chirped pulse to yield an instantaneous Doppler frequency (which indicates target velocity) and a rate of change in the instantaneous Doppler frequency (which indicates target acceleration).

Abstract: A pseudorandom noise coded system (100) compensates for imperfections, improving out of range rejection, and includes a digital correlator (200) having a first complex multiplier (202) receiving a sequence of sampled data words and a sequence of precomputed complex data words and producing a sequence of first complex product words. A second complex multiplier (204) receives the sequence of first complex product words and a precomputed constant word and produces a sequence of second complex product words. A complex multiplexer (206) receives a sequence of binary code states, and the sequences of first and second complex product words and produces a sequence of complex multiplexer output words formed as a replica of either the first or the second complex product words, depending on the binary code. A complex accumulator (208) receives the sequence of complex multiplexer output words and produces a complex accumulated sum word formed as a complex sum of the complex multiplexer output words.

Abstract: This invention relates to a method and apparatus for controlling a biphase modulator (602, 702) to improve autocorrelation in pseudorandom noise coded systems. The biphase modulator modulates a carrier frequency with one of two phase states responsive to a pseudorandom noise (PN) binary code sequence. The spectrum (610, 710) at the output of the biphase modulator comprises a plurality of spectral lines separated by the code repetition frequency, including a center spectral line (611, 711) and at least one adjacent spectral line (612-615, 712-717). The magnitude of the center spectral line is measured and compared to a reference to produce a control signal which is responsive to the magnitude of the center spectral line. This control signal is supplied to the biphase modulator for maintaining a predetermined magnitude of the center spectral line thereby achieving a desired spectrum output and improving autocorrelation of the system.

Abstract: A distance measuring method and apparatus in which first and second pseudo random signals which are the same in pattern but slightly different in period are generated to obtain a correlation output of the first and second pseudo random signals before transmission thereof as a reference correlation output, and the first pseudo random signal is directly transmitted toward a target or alternatively a carrier wave is modulated by the first pseudo random signal and transmitted toward the target. A correlation output of the signal reflected and received from the target and the second pseudo random signal is detected and the distance to the target is measured from the time interval between the reference correlation output and the received correlation output.