Abstract: Coherent, frequency multiplexed radar is a new generic type of continuous wave radar architecture wherein contiguous pulses of discrete frequency segmented signals are serially transmitted from an antenna, and after reflection from radar targets, signals from the same antenna are coherently processed in a parallel manner to provide correlated measurements of target's pulse compressed range and radial velocity. Simultaneously transmitted and received signals are separated by frequency multiplexing.

Abstract: The present invention overcomes the problems discussed above by providing a linearizer apparatus for providing a linear ramp modulation for a voltage control oscillator (VCO), including voltage controlled oscillator means (VCO) having input and output terminals, and means for producing the output signal at its output terminal at the output frequency such that the output frequency corresponds to the voltage of a modulated tuning signal applied to the input terminal. A signal division means is coupled to the output of the VCO for producing a divided signal. A glass bulk acoustic delay means is coupled to the signal division means for producing a delayed signal. A first comparison signal generator means is coupled to the divided signal and the delayed signal for producing an IF signal which is proportional to the VCO output signal non-linearities. A reference oscillator means is provided for producing a reference signal.

Abstract: In an FM-CW radar system, a beat signal is frequency-analyzed for selecting ascending-side beat frequencies and descending-side beat frequencies for a plurality of targets. By pairing the ascending-side and descending-side beat frequencies one by one from each side, all possible combinations thereof are prepared. Based on these beat frequency combinations, beat frequency combinations after a given time are predicted, respectively. If an ascending-side beat frequency and a descending-side beat frequency of the predicted beat frequency combination are found in ascending-side beat frequencies and descending-side beat frequencies of a beat signal selected after the given time, respectively, or in the neighborhood of them, respectively, the predicted beat frequency combination of the found ascending-side and descending-side beat frequencies is set as a correct beat frequency combination. A further correct beat frequency combination/combinations can be set in the same manner.

Abstract: Improved performance in electronic countermeasure systems that utilize main lobe shifting techniques to jam track while scan threat radars are achieved through the use of a modulation sweep program that overcomes scan rate frequency and phase uncertainties. The modulation sweep program is used in conjunction with a conventional swept repeater modulation program. The modulation sweep program is disabled and the swept repeater modulation program is enabled when constant illumination sources or track while scan saturation conditions are encountered.

Abstract: An FM radar system of more simple construction, smaller size, lower cost and improved performance is provided in which circulators of any type in the prior art are eliminated by constructing a transceiver comprised of a transmitting part and a receiving part, each formed on a common dielectric plate and having a dedicated transmitting antenna and a dedicated receiving antenna respectively. The antennas comprise planar array antennas, in contrast to the solid antennas used in prior art systems. The planar array antennas are also formed on the single dielectric plate. The transmitting part comprises a plurality of transmission antennas and a plurality of frequency multipliers coupled to said transmission antennas. The receiving part comprises a plurality of receiving antennas which are coupled to a plurality of switches through a plurality of mixers, frequency multipliers, and low noise amplifiers.

Abstract: A FM-CW radar device is provided for frequency-modulating a high frequency signal with a modulation signal, transmitting the modulated high frequency signal, receiving a signal reflected by a target object and frequency-modulating the reflection signal with a signal generated by a local oscillator signal source provided by branching a portion of the transmitting signal. A modulator is disposed between a radar transmitting section and a transmitting antenna. The modulator modulates the transmitting signal with a second frequency which is far lower than the radar transmitting frequency and twice as much as the sum or the difference of a Doppler frequency generated by a relative propagation velocity and a beat frequency generated by a propagation delay time. A first frequency converter frequency modulates the received signal reflected by the target object with the local oscillator.

Abstract: A closed loop linearizer method and apparatus for providing a linear ramp modulation for a voltage controlled oscillator (VCO). A counter is connected to the VCO for calculating two frequency values of the oscillator at one or more time points during a ramp interval. The difference of the two frequency values is then compared with that of a predetermined ideal difference frequency value. A resulting correction value is then generated and used to adjust digital control values upward and downward, thereby causing the VCO to produce a linear modulation ramp output slope over time.

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 transmitter/receiver system is provided wherein a transmitter of such system produces a transmitted signal frequency modulated in accordance with the level of a modulating signal and a receiving antenna has an output thereof coupled to a receiver through a switch means, for coupling or inhibiting signals received by the receiving antenna from passing to the receiver selectively in accordance with the level of the modulating signal.

Abstract: A compact radar sensor is provided. A monolithic millimeter wave integrated circuit (MMIC) transceiver is provided having a transmitter for transmitting a frequency modulated signal and a receiver for receiving reflected signals thereof. A microstrip patch antenna is provided for transmitting signals within a desired field and receiving the reflected signals from objects therein. A digital signal processor is further provided for analyzing the received signal and providing output signals therefrom.

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 segmented stretch waveform for wide band high duty cycle tracking application. The waveform is divided into multiples of two spaced segments as the tracking range closes. Target returns received during spaced segments are combined to correspond to the complete waveform; and range is determined in accordance with the combined waveform. Tracking range can be varied without changing bandwidth, FM slope, duty cycle or processing time.

Abstract: A method for characterizing frequency modulation rate parameters for a swept frequency signal is based on zero crossing counting and digital signal processing. The method is easy to implement and does not require batch processing so as to be suitable for real time tracking of frequency variations in a variety of applications.

Abstract: A voltage controlled oscillator is disclosed in a "ring" configuration using two BJTs. The design uses an active feedback topology which eliminates the need for a tank circuit for oscillation to occur. The design also provides for the mixing function to be performed by one of the BJTs.

Abstract: For use in a spread spectrum communication system there is provided in an embodiment of the invention a spread spectrum transmitter which uses a voltage controlled oscillator (VCO) for generating a carrier signal wherein the frequency of the oscillator is controlled by the output of a correlation code generator and data generator coupled to a varactor in the oscillator. The use of a VCO eliminates the need for sidelobes associated with mixers. In another embodiment the separation of the output of the correlation code generator and data generator coupled to the varactor and the output of a phase detector coupled to the varactor simplifies tuning of the transmitter and in another embodiment the use of a high gain differential amplifier to couple the output of the correlation code generator and data generator to the varactor eliminates tuning the transmitter.

Abstract: For use in a spread spectrum communication system there is provided in an embodiment of the invention a spread spectrum transmitter which uses a voltage controlled oscillator (VCO) for generating a carrier signal wherein the frequency of the oscillator is controlled by the output of a correlation code generator and data generator coupled to a varactor in the oscillator. The use of a VCO eliminates the need for sidelobes associated with mixers. In another embodiment the separation of the output of the correlation code generator and data generator coupled to the varactor and the output of a phase detector coupled to the varactor simplifies tuning of the transmitter and in another embodiment the use of a high gain differential amplifier to couple the output of the correlation code generator and data generator to the varactor eliminates tuning the transmitter.

Abstract: It has been proposed in accordance with the invention to determine the linearity of the modulated oscillator frequency of an FMCW radar by means of the Hilbert transformation and to supply a control voltage, corresponding to the deviation, to the controllable oscillator via a digital/analog converter. A control and computing unit is used to determine the linearity of the modulated oscillator frequency.

Abstract: A circuit for generating an output signal having an output frequency that varies linearly with time, and to an FM CW radar system utilizing such a circuit. The circuit includes a voltage controlled oscillator that produces an output signal at its output terminal at an output frequency that corresponds to the voltage of an input tuning signal. A comparison signal circuit receives the output signal and produces a periodic comparison signal such that when the output frequency varies by .DELTA.f, the comparison signal frequency varies by .DELTA.f/N where N is a positive integer. An update counter periodically causes the value of N to change by a predetermined integer amount. A phase detector compares the comparison signal to a periodic reference signal, and produces a correction signal that is filtered to provide the tuning signal for the VCO. The value of N is preferably changed at an update frequency that is equal to the frequency of the reference signal times an integer.

Abstract: FMCW radar return signals are converted to i.f. in a front end section, digitised in an A-D converter, and reduced to in-phase and quadrature base band components at a lower sampling rate in a filter section. Returns are compared with a separate reference waveform signal from a generator for each range cell by a multiplier and an accumulate and dump function. The reference waveforms for subsequent range cells are delayed by one sample period. The provision of separate correlation of de-ramping for each range cell enables non-linear sweep wave forms to be employed, whereas the conventional method using a single Fourier Transform for all range cells simultaneously restricts operation to a linear sweep waveform.

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: When linearizing FMCW radars it is customary to produce a synthetic target signal independently of the radar signal and to use the synthetic target signal to linearize the sweeping of the transmitted VCO frequency or the sampling of the radar IF signal to be analyzed. In order to reduce the overall number of microwave RF components, the present invention uses one mixer (18) to produce the radar IF and linearizing IF. In one embodiment an RF STALO (32) is coupled by a directional coupler (34) into the return path of the radar signal. In other embodiments (not shown) the mixer comprises a dc biased waveguide harmonic mixer and the STALO generates a lower frequency which is applied to the mixer by way of either the bias port or the radar IF output port. The linearizing arrangements (28) disclosed are based on known designs.

Abstract: The frequency-versus-time characteristic of the output signal of a swept-frequency radar is linearized by determining departures from linearity of the phase-versus-time characteristic of the beat signal obtained between an actual return from a selected radar target and a sample of the current radar output signal, and applying oppositely-directed corrections to the frequency-versus-time characteristic. The relevant beat signal is selected from the output signal of a mixer (8) by performing special analysis in a Fast Fourier Transform (FFT) calculating circuit (15) and then performing an inverse FFT on a windowed portion of the FFT obtained. A second or higher-order polynomial is then fitted to the phase-versus-time characteristic of the selected beat signal after it has been expressed as time versus phase, and correction terms are derived from the coefficients of this polynomial. The radar output signal is generated by a voltage-controlled oscillator (1) controlled by a control voltage generator (7).

Abstract: Linearizing circuitry for an FMCW transmitter (1,2) employing a linear modulation waveform. The output signal is sampled (3,4,5) in successive intervals, small compared to the modulation period, and a cycle count (16) taken in each interval; a reference count is derived for each interval, either by way of a look-up table (21) triggered by a clock count (17) or derived by way of a clock driven processor (18). A comparison (20) is made and any error (22) is used to control (11) the phase of the modulation waveform.

Abstract: Range resolution in an FMCW radar system is achieved by providing a periodic linear frequency sweep. The present invention assures the linearity of this sweep by using a negative feedback circuit which includes means for obtaining 16 sequential instantaneous frequency versus time slope measurements during each sweep cycle, generating a set of 16 sequential error signals and a corresponding set of correction voltages, and applying these correction voltages to the sweep drive voltage used to drive the voltage controlled oscillator that generates the frequency swept output signal.

Abstract: A voltage controlled oscillator (VCO 10) is disclosed in a "ring" configuration using two FETs. Two isolated voltage control terminals provide increased tuning bandwidth. The design uses an active feedback topology resulting in greater device size for higher output power and circuit Q.

Abstract: A continuous wave radar system comprises a transmitter section (1), a receiver section (2) and a common transmit/receive aerial (3). A directional coupler (12) is used to couple the transmitter section output (9) to the aerial (3) and to couple the aerial (3) to a first input (5) of a mixer (4) included in the receiver section (2). A second input (6) of the mixer (4) is fed with a reference signal from the transmitter section (1) via a fourth port (17) of the coupler (12), thereby usefully utilizing at least some of the transmitter power which would be wasted were the fourth port (17) merely terminated in a matched impedance.

Abstract: Apparatus for detecting FM signals, such as from a radio altimeter, is disclosed. The apparatus contains a phase detector which has as inputs the received signal and a delayed replica of the input signal. The output of the phase detector is filtered in a filter bank, the outputs of which feed a logic circuit. The logic circuit selects the output with the largest signal level. If the selected output has a level exceeding a threshold, the presence of an FM signal is indicated.

Abstract: An apparatus and method for identifying sidelobe transmitted and/or received radar signals. The apparatus is utilized in a radar system having a transmitter for generating at least one detection signal, an antenna system defining a mainbeam and sidelobe radiation pattern for transmitting each detection signal and for receiving electromagnetic signals including echo signals each corresponding to a reflection from an object of a transmitted detection signal, and a receiver system for processing each received echo signal. The apparatus is embodied as a system for identifying each echo signal received upon the antenna system sidelobe and each received echo signal having a corresponding detection signal transmitted on the antenna system sidelobe.

Abstract: A system for transmitting a comb of radar signals. The invention includes a phase shifter for shifting the phase of an input carrier signal. A frequency modulation signal is adjusted in amplitude by an attenuator 16 and input to a balanced mixer 14. The balanced mixer 14 mixes the input carrier signal with the attenuated frequency modulation signal. A summer 20 combines the output of the phase shifter 12 with the output of the balanced mixer 14. The system 10 of the present invention provides an inexpensive means of generating and receiving a complex of illuminating signals having a spread spectrum consisting of lines (teeth) of carrier frequencies with controllable power. The system 10 is agile in that the power levels and the spectral positions of the teeth may be varied.

Abstract: A signal processing system for collecting and outputting samples of a signal; in which the system has a memory into which the samples are written such that when the memory is read the samples are read sequentially and always in the same frequency order, irrespective of the arrival sequence of the different frequencies.

Abstract: A radar system comprises a radar carrier frequency oscillator for producing a radar carrier signal, a receiver including a mixer for producing Doppler signals, a Doppler filter bank and an alarm circuit, including a series of Doppler bins, having an alarm threshold level. The radar system is provided with a frequency modulator for modulating the radar carrier signal and any interference signal received by the receiver whereby the bandwidth of the frequency modulated interference signal exceeds the bandwidth of a number of Doppler filters in the Doppler filter bank. The alarm circuit may have two threshold levels and may be controlled in dependence upon a predetermined pattern of crossings of the threshold levels.

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: A multi-frequency comb generator (2-4; FIG. 1) for radar and the like using a feedback loop through a frequency multiplier, such as for example, a doubler (3). A reference or master oscillator output goes through a directional coupler (2), for example, a ten dB coupler with twenty dB directivity, to the frequency doubler and then an amplifier (4). The amplifier output is superposed on the reference oscillator output (1) and is applied to the input of the doubler. Frequency doublers, when driven by multiple frequencies, cross modulate and generate sum and difference frequencies, which in going around the loop are fed back to the input, resulting in a comb of frequencies (5). As part of the frequency selecting section of a radar exciter (FIG. 2) the comb of frequencies and the output of a parallel frequency multiplier (8) are fed to a mixer (7), and the mixer's output, along with the coupled output ("N.times.

Abstract: The invention relates to a radioaltimeter type detector comprising an oscillator-transmitter (10), a modulator (20) suitable for frequency modulating the oscillator-transmitter according to a given characteristic, a mixer receiving the signal from the oscillator-transmitter and a corresponding echo signal reflected by a target, and a discriminator circuit (50, 60) connected to the output from the mixer. According to the invention, the modulator (20) includes a digital memory (21) containing a series of values defining the frequency modulation characteristic of the oscillator-transmitter (10).

Abstract: The present radar altimeter operates in accordance with the frequency modulated continuous wave principle in the C-band. The altimeter is constructed with microminiaturized integrated circuits and provides a completely digital signal evaluation and mode control which enables the transmitter to produce a wave-form providing the altimeter with the following advantages. A silent mode during the signal evaluation greatly improves the resistance of the altimeter against electronic countermeasures. The transmitter frequency is stabilized and a compensation for Doppler frequency drift is provided. Further, the altimeter is able to discriminate between intended proper targets on the one hand and false or erroneous targets on the other hand. The altimeter is equipped with a self-testing unit which provides different functions in different modes.

Abstract: Doppler shift generator for use in electronic countermeasures equipment includes analog memory devices which are comprised of acoustic charge transport (ACT) memory devices. Such Doppler shift generators includes a switch which alternately applies an input signal to said first and second analog memory devices. Each analog memory device is responsive to a clock signal to sample data at a first frequency and to output the data at a second frequency. As a result, a Doppler shifted signal is generated whose frequency has been shifted by the difference in the first and second frequencies.

Abstract: An input signal for a travelling wave or distributed amplifier having input and output transmission lines is supplied to one end (1) of the input line and an output signal is derived from one end (4) of the output line. Conventionally, the other end (2, 3) of each line is terminated in a respective matched load, but three ports of the amplifier may be employed. The travelling wave amplifier may be used to replace a circulator (CIRC, FIG. 2) in an FMCW radar having a single transmitting/receiving antenna (ANT) (TWAMP1, FIG. 3), to replace a directional coupler (DC) for supplying a local oscillator signal to a mixer (MXR) (TWAMP2, FIG. 4), and in combination with a mixer diode (D) to form a mixer amplifier (TWAMP3, FIG. 3), giving the possibility of the larger-scale integration of RF circuits.

Abstract: A continuous wave radar system arrangement for improving the dynamic range of the radar receiver. The transmitted carrier signal is frequency modulated by a periodic sawtooth waveform causing a predetermined peak frequency shift. The radar receiver includes a plurality of separate receiving channels each selective to a small portion of the transmitted bandwidth. As the sawtooth modulation causes the carrier signal to sweep in frequency, the received leakage and clutter signals in the selective receiving channels are blocked momentarily and individually in each channel. The outputs of the separate receiving channels are combined to form a composite signal of the echo returns. Gaussian filters with quadratic phase compensation are used to provide the selectivity of the receiving channels.

Abstract: A fiber optic device 50 designed to steer the radiation beam of a phased-array antenna 10 has been demonstrated. A radio frequency (RF) signal is generated via photomixing at the output of a single-mode fiber optic interferometer. The phase of the electrical signal is shifted over several cycles in direct proportion to a voltage applied to an optical modulator 34, 60. The modulator consists of a Pockels-type optical phase modulator located in one arm of the heterodyne interferometer. Rapid changes in RF phase are feasible. A miniature low-voltage version of the device 50, 72, based upon integrated optics, has been devised.

Abstract: Signals to control the signal processor in the linearizer of a frequency modulated continuous wave radar transmitter are generated by sampling the signal being transmitted, modulating and delaying this signal, mixing the modulated delayed signal with a second sample of the signal being transmitted to obtain an intermediate frequency signal, filtering the intermediate frequency signal to isolate the upper and lower sidebands of this signal and mixing the two sidebands to obtain a control signal having a frequency that varies directly with the beat frequency between the sampled and delayed signals.

Abstract: In an optically controlled phased array radar control information in the form of microwave frequency modulation of an optical carrier is transmitted by optical waveguide from a central processor to each of the antenna elements. Phase shifts introduced by each of the individual waveguides are then monitored to provide a compensation signal used either to regulate the phase shift or to offset the phase of the modulation applied to the waveguide at the central processor end.