Abstract: The invention relates to a device for the linearization of a frequency modulation ramp comprising a voltage controlled oscillator associated with a phase locked-loop. The device comprises a digitally controlled oscillator of which only the most heavily weighted bit is used, and a digital phase comparator receiving, on the one hand, said most heavily weighted bit and, on the other hand, a signal supplied by the voltage controlled oscillator. Application to very high linearity and very high accuracy radio altimeters.

Abstract: A radio altimeter using a linear oscillator to transmit a saw-toothed signal comprises, in addition to this first oscillator, a second linear oscillator to transmit, in synchronism with the first linear oscillator, another saw-toothed signal with a given saw-tooth duration Td. The plateaux of the sawteeth of the two saw-toothed signals are at a distance from each other equal to a value f. The test consists in obtaining a height h′ by beats between the two saw-toothed signals and computing a standard height he=f.c.Td/dF.2 where c is the speed of light and dF the duration of each saw-tooth of the other signal. Application to all FM/CW radio altimeters.

Abstract: FMCW doppler radar, in which a reference signal is generated from the transmit signal via a delay line and a mixer. A measuring signal which is received and mixed with the transmit signal is detected and digitized at the times of the zero crossings of the reference signal. In this way, the measuring signal can be evaluated at time intervals of equal phase of the reference signal. A downstream algorithm enables the generation of a strictly linearly frequency-modulated transmit signal. With this mechanism, phase errors of conventional radar systems are eliminated.

Abstract: The invention proposes a novel method for using the signals provided by an airborne FM/CW radio altimeter, allowing to perform an analysis of the ground overflown by an aircraft for the purpose of, for example, identifying it, or alternatively of recognizing it. The method of the invention consists in analyzing, in the frequency domain, the shape of the spectrum of the beat signal generated by said radio altimeter to characterize said ground so as to extract from it information relating to the reflectivity of said ground.

Abstract: A spectral analysis carried out on the beat signals obtained by the mixing of a transmission signal, the frequency of which is modulated in the form of recurrent sawteeth, with this same signal after it has been transmitted, reflected and then received. The spectral analysis is based on the computation of self-correlation coefficients enabling the definition of the spectral components. For this purpose, the coefficients are computed at each sawtooth and are combined with the coefficients determined with the most recent previous sawteeth to give so-called global coefficients, from which the spectral components sought are restituted in a conventional way. Application especially to altimeters for the measurement of small heights.

Abstract: In a distance measurement to an object, the distance measurement operating according to the FMCW principle, a linear frequency-modulated signal is transmitted and mixed with the signal reflected back from the object, generating a demodulation signal with a frequency proportional to the distance. To determine the distance, at least one estimation signal with an assumed frequency and a variable phase is generated and an estimation error is determined by comparison of the transmitted signal and the estimation signal. The phase of the estimation signal is adaptively varied for the purpose of an error reduction and the frequency of the estimation signal is corrected corresponding to the variation of the phase over time, the distance being determined from the frequency corrected in this manner.

Abstract: An altimetric type measurement method for use on a satellite transmits a pulse towards the surface of the sea and carries out frequency transformation on the return signal resulting from the reflection of this pulse at the surface of the sea. This produces a spectral signal of samples successively comprising:(a)--a first zone with a low amplitude level,(b)--a second zone with a sharply increasing slope ending at a peak, and(c)--a third zone of decreasing slope.Samples of the spectral signal are selected within a selection zone that corresponds to the first and second zones for a predetermined maximal level of the height of the waves at the surface of the sea and maximum likelihood processing is applied only to the selected samples.

Abstract: A continuous wave radar altimeter comprises a memory (24, 26), means for storing in the memory in digital form an array of return signals representative of the variation of reflected amplitude with path length, means (27), for addressing the memory for identifying a peak return representative of the highest objects on the terrain, means (28) responsive to the array for determining the signal-to-noise ratio thereof, and means (29) responsive to the height at which the said peak return occurs and to the signal-to-noise ratio to determine a "center of area" height representative of the lowest surface on the terrain. The altimeter thus provides not only the peak level, representing for example the tops of trees and buildings, but also the ground level.

Abstract: A relatively low-cost FMCW radio altimeter includes a voltage-controlled oscillator based upon a GaAs FET. The oscillator produces, for example, a 4.3 GHz microwave signal that is modulated with a triangular wave having a pin-selectable modulation frequency. The modulated signal is amplified by a buffer amplifier, as well as a power amplifier, and connected to an RF output terminal by way of a plurality of microstrips. Reflected signals are received at an RF input and are coupled to a mixer by way of a low-noise amplifier. The modulation signal is also applied to the mixer by way of a microstrip coupling device to produce an audio output signal whose frequency is proportional to the altitude above ground. The gains of all of the amplifiers are selected to eliminate the need for hand-tuning of the microstrips and to enable the use of a glass/epoxy circuit board.

Abstract: A low cost frequency modulated (FM) radar altimeter system with enhanced accuracy for continuously providing an altitude of a target, comprising a transmitter means for transmitting a carrier modulated output signal towards the target; a receiver means having an altitude output signal for receiving the carrier modulated output signal reflected from the target after a time delay, and for providing an open loop error correction means for correcting errors resulting from nonlinearities in the transmitter means and signal processing delay variations in the receiver means so that the altitude determined is accurate; a coupling means for directing a portion of the carrier modulated output signal to the receiver means, and searching means having a first output directed to the receiver means and a second output directed to the transmitter means and having a symmetrical search output signal with a slope, s.sub.

Abstract: A microwave transceiver using a reflection pumped mixer includes an electromagnetic signal generator, a subreflector, a reflector of electromagnetic signals from the subreflector, a mixer, circulator, and processing circuitry to relate electromagnetic signal frequency differences to the range of a target from the transceiver. Such frequency differences are detected by the mixer from the captured electromagnetic signals reflected distant targets and reflected electromagnetic signals from the subreflector.

Abstract: A method and apparatus for determining an altitude for a radar fuze. The method includes the steps of receiving a return signal and transmitting a transmitted signal. The return signal and the transmitted signal are mixed and a mixed signal representing an altitude is responsively generated therefrom. The mixed signal is amplified to generate an amplified signal. The amplified signal is filtered to generate a filtered signal which is envelope detected to provide a detected signal responsive to the filtered signal. The detected signal is integrated responsively to the detected signal. The integrated signal level is compared against a track threshold reference signal and a track/no-track comparator signal is provided responsively to the integrated signal level and the track threshold reference signal. System timing is controlled by generating a plurality of control signals responsive to the track/no-track comparator signal and proportional to an altitude.

Abstract: In the method of the invention, a microwave signal is passed through a material whose moisture content is to be measured, the change in the velocity of the signal which has travelled through the material is measured and the moisture content is determined on the basis of the measured change and a known interdependence between the changes in the microwave signal velocity and the moisture content of the material. The apparatus comprises a transmitting device (1) which transmits a microwave signal through the material to be measured, and a detecting device (2) and a counting device (3) which measure the change of velocity of the signal transmitted through the material and determine the moisture content of the material on the basis of a known interdependence of the change of velocity of the microwave signal in question and change of moisture content of the material.

Abstract: The present invention provides a cavity examination method of a paved road which can examine cavities which are present under the paved road such as the asphalt-paved road in a reduced length of time. By collecting data of the structural conditions of areas under the paved road while traveling on the road by a pavement structure examination vehicle mounted with underground radar means, and scrutinizing according to the above results around the place which may contain a cavity by a pushcart type underground radar means, the cavity examination method of the present invention specifies presence and a planar extent of the cavity. If a cavity is actually detected, a hole with a small diameter is bored in the place and its inner circumferential wall is photographed by a camera to confirm the conditions of the cavity and the area under the pavement by a visual inspection in order to grasp the three dimensional conditions of the cavity.

Abstract: This radar system for measuring the nearest distance "h" comprises transmitting means (9, 7, 5) for transmitting towards an object a frequency-modulated wave, receiving means (15, 17) for receiving the wave after reflection by the object, mixing means (20) for producing a beat-frequency wave between the transmitted wave and the received wave, high-speed digital processing means (30) for effecting a time-frequency transformation operation of the beat-frequency wave; it further comprises management means (50) for providing the user with the value "h" by influencing more specifically the transmitting means and the high-speed digital processing means.

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: An aircraft radar altimeter includes a programmed microcontroller which permits effective simultaneous tracking of at least two targets such that, for example, both ground and obstacles on the ground can be simultaneously tracked, thus avoiding crashes when the aircraft is operating at very low altitudes. The microcontroller is operatively coupled to the radar transmitter and to the receiver so that information relating to a first target can be stored away while a search and track operation is run on a second target. The information concerning a detected second target is likewise stored away and the microcontroller permits alternate tracking of the two targets with the stored information being used as the basis for establishing an initial position for a target when tracking of that target is resumed.

Abstract: A low altitude radio altimeter of the FM/CW type which transmits a sawtooth frequency wave and has a transmitting and a receiving aerial. A beat frequency signal Fb.sub.t between the transmitted and received waves is produced at the output of a mixer. The altimeter includes means for digitizing Fb.sub.t at the rate of n samples per sawtooth, a first memory (M1) to store n.times.k samples S.sub.j.sup.i (where i varies from 1 to k and j varies from 1 to n), a second memory (M2) to store n sums ##EQU1## first computing means (PR) for determining ##EQU2## representative of Fb.sub.4, for storage in a third memory (M3), and additional computing and storage means (PR, M4) producing difference signals Fb.sub.t -Fb.sub.f.

Abstract: The device comprises, in a control loop of the subtractive beat frequency fb between transmitted waves and waves received as an echo, a pursuit discriminator (11) establishing the frequency fb at f.sub.0 and a pursuit validation circuit (12). This device is characterized by the combination of a contrast discrimination set (CDS (15 to 18) and a VSE discrimination set (21 to 25) for detecting energy in a guard band situated at the upper end of the frequency bands of the CDS, the latter comprising a contrast discriminator (15), a first attenuator (16) and controlling the pursuit validation circuit (12). The VSE discrimination set is arranged for controlling the gain of the first attenuator (16).

Abstract: A transmitter section of the arrangement includes an altimeter transmitter and a Doppler transmitter. The transmitters both provide frequency-modulated outputs. The altimeter transmitter is linear-FM while the Doppler transmitter is sine-FM.

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 radar system of the FM/CW type transmits a wave which has a virtually linear frequency, between two frequencies f.sub.1 and f.sub.2 and supplies a first beat signal (Fb.sub.1) between transmitted and received waves; it is suitable for measuring the altitude h by measuring the overall phase rotation. According to the invention the radar supplies a second beat signal (Fb.sub.2) in quadrature with the first signal; the signals Fb.sub.1 and Fb.sub.2 are digitized (23 to 26) and comparing means (36) compare the consecutive samples of Fb.sub.1 and Fb.sub.2, then calculating means (37) derive therefrom by means of successive increments/decrements the number of zero crossings of the phase plane in a predetermined direction minus the number of zero crossings in the opposite direction (result m). The calculated altitude h is proportional to m.

Abstract: A measuring apparatus for detecting the distance h to an object transmits and receives returns of a linearly frequency-modulated wave obtained by means of an oscillator (5) and a signal generator (7). A beat frequency signal is obtained by mixing the transmitted and received waves. The beat frequency signal at the output of mixer (22) is sampled and digitized by a signal sampler (30). The height "h" can be estimated by analyzing the frequency spectrum of this beat frequency wave. This spectrum is provided by the formula: ##EQU1## in which formula the coefficients a.sub.i are those of a p-order predictor. This predictor provides a digital estimatin of a beat frequency wave sample on the basis of p previous samples.

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: The invention relates to an FM-CW radar apparatus where the frequency sweep duration (R) corresponding with the transmitted signal is increased to obtain a mixing signal which is operational in a wider frequency range than the frequency sweep of the transmitted signal. This has the effect that processing of echo signals of sufficient length can be realized, also from objects which are located near the limits of the radar range.

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 laser radar system wherein a beam of continuous wave (CW) electromagnetic energy is generated with frequency modulation (FM) and amplitude modulation (AM) being imposed thereon to produce an amplitude and frequency modulated, continuous wave beam of energy. The AM-FM CW beam is transmitted toward a selected target, portions of the transmitted beam being reflected by the target and received along with portions of the transmitted beam reflected by unselected targets and atmospheric clutter. A first signal is produced in response to the frequency modulation on the received beam portions reflected by the selected target, such first signal representing the approximate range of the selected target and substantially resolving the selected target from unselected targets and atmospheric clutter and having a relatively long ambiguous range interval.

Abstract: A Doppler navigation system includes an altimeter section with increased accuracy resulting from closed loop operation of signal processing portions for reflected signals including phase shift information. Quadrature processing of the reflected signal includes compensation for differences between quadrature processing channels, wherein the reflected signals are periodically processed by alternate ones of the channels. A maximum amplitude signal is forwarded by the signal processing portions to a frequency tracker of the navigation system. Periodic calibration of the altimeter section corrects for delays introduced in the signal processing portions. Effects of FM to AM conversion in a Gunn oscillator are reduced by connection of the signal processing portions to a short circuit during the calibration periods.

Abstract: This radar device for measuring the distance h of the device to a surface (2) includes transmission means (5) for transmitting to the surface a frequency-modulated wave E(t) provided by an oscillator (14) having a frequency control, receiving means (7) for receiving this wave R(t) reflected from the surface, a mixer circuit (10) for producing a beat wave between the transmitted and received waves and a processing circuit (20) including a beat-wave-digitizing circuit (25) and a time-frequency transform operator (27) for supplying frequency components from which the distance h is determined. This processing circuit (20) further includes an auto-correlation operator for effecting an auto-correlation of the beat wave digitized by the circuit (25) and also spectrum processing means (32) for finally determining the distance h.

Abstract: A frequency modulation radio altimeter has a directional antenna which is connected to a transmission-reception switch controlled by a signal generator. The generator delivers periodic signals whose recurrence period is proportional to the delay time of the ground echo. The transmitter includes a radio frequency modulator modulated in frequency by a saw tooth signal whose recurrence period is proportional to the delay time of the ground echo. A homodyne receiver includes circuits for acquiring and tracking the ground echo signal, and supplies an output signal representative of the altitude and a control signal which is supplied to the inputs controlling the recurrence period of the transmission modulator and of the generator controlling the transmission-reception switch.

Abstract: A Radar Altimeter signal presence circuit which provides improved useable system sensitivity for a given false track probability by providing an improved method for detecting the adequacy of the return signal. This return signal is composed of many small, rapidly changing reflections that vary between additive and substractive combination giving the net return the characteristic of noise. A non-linear detector is used to enhance the signal presence detectors sensitivity to weak but adequate returns while (1) reducing the ability of short periods of strong returns to cause a positive signal presence indication when the overall signal is inadequate, and (2) retaining a high sensitivity to periods of signal fades that produce measurement errors. This is accomplished by using a non-linear detector that reduces the effect of strong returns when the many small reflections tend to combine additively, and increases the effect of weak returns when the many small reflections tend to combine subtractively.

Abstract: A Radar Altimeter static accuracy circuit which provides improved system accuracy when the altimeter platform is stationary over the ground. Most often this stationary condition occurs in helicopters while hovering at low altitudes but also occurs, for example, in altimeters used to measure the level of grain in elevators. The altimeters output, a voltage proportional to altitude, is used to control a voltage controlled oscillator (VCO), the output of which is summed into the receiver intermediate frequency (IF) amplifier output to fill in the return signal fades. These fades otherwise cause altitude processor errors leading to erroneous altitude measurements. The VCO is adjusted to produce an output frequency equal to the IF amplifier output frequency.

Abstract: Apparatus for reducing the composite coupling signal in a frequency modulated, continuous wave radar having a single antenna and a duplexer includes a modulation signal generator coupled to a continuous wave oscillator to provide input to the duplexer. A directional coupler at the duplexer input provides input to an adjustable phase-shifter which provides a phase-shifted signal to an RF mixer. The RF mixer receives a second input from the output of the duplexer and provides a mixed signal. A level modulator having an adjustable control input receives a portion of the modulated signal from the modulation signal generator. The level modulator then provides an output to the audio amplifier which also receives the mixed signal from the RF mixer. The audio amplifier provides an output signal having reduced composite coupling signal components.