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: An arrangement for determining the starting instant t.sub.o of the leading edge of a received high-frequency pulse signal V of the formV=A.(t-t.sub.o).sin 2.pi.Ft,whereV is the instantaneous voltage,A is the slope (which is unknown) of the leading edge,t is the time, andF is the frequency.The arrangement includes delay means for delaying the received pulse by a period of time equal to k/2F (where k is an integer) and for thus producing a second pulse signal V.sub.R of the formV.sub.R =A.(t-t.sub.o -(k/2F)).sin 2.pi.[F(t-(k/2F))]The pulse signals are applied to calculating means which determines t.sub.

Abstract: An aircraft is equipped with a system of the FM-CW type including an on-board radio altimeter which cooperates with a transponder/beacon located at A. The radio altimeter is adapted for the measurement, alternately with the measurement of the altitude H, of the distance D in relation to point A, and of the angle .beta. in relation to a horizontal axis (46) linked to the transponder. The radio altimeter includes two aerials and a supplementary processing chain for the measurement of angle .beta.. The transponder is equipped with a base with two receiving/transmitting aerials (25, 27), switched alternately to sequentially operated circuitry in the transponder. Furthermore, the exact position of the aircraft within the vicinity of point A is determined by at least two measurements of distance D and of the angle .beta. in relation to the aerial base of the transponder.

Abstract: An aircraft position determining system including an on-board radio altimeter which cooperates with a ground based transponder/beacon located at a position A. The radio altimeter is adapted as a distance meter and comprises means (9, 14, 15, 16) for shifting the frequency of the local oscillation signal. The system has a range sufficient to enable it to operate in a second predetermined volume defined with respect to the position A which includes a first volume defined by the lateral distance accuracy (d) and vertical distance accuracy (h) of the position determined by an independent on-board guidance device. The exact position of the aircraft when close to A is determined by at least two successive measurements of distance from to the position A.

Abstract: A simulator is provided for testing a radio altimeter of the type which emits a frequency-modulated wave, the modulation being according to linear segments of slope p, and which compares the frequencies of the emitted wave and of the wave which is received after reflection to provide a distance measurement. The simulator according to the invention is connected between the transmitting antenna and the receiving antenna of the altimeter, and comprises two signal-processing chains which are arranged, in parallel, between a receiving section and an SSB mixer, the output terminal of which is connected to a transmitting section. The first chain is formed by first devices, which generate a quantity G, which is proportional to p, and second devices, which generate a signal possessing a frequency f.sub.d, the ratio of f.sub.d and G assuming a predetermined, adjustable ratio, Q. The second chain is formed by a coupler which is connected to a variable attenuator.

Abstract: A digital-to-analogue converter arrangement employs a digital-to-analog converter circuit (10) of a type producing an output voltage V(n') such that: ##EQU1## where k is a constant, E is a voltage applied to a reference voltage input, n' is a binary number applied to a binary signal input and M' is the maximum value n' can attain. The converter arrangement includes a negative feedback network (20) coupled between the output (13) of the digital-to-analogue converter circuit and the reference voltage input (14).

Abstract: A radar system operating by means of frequency-modulated pulsed waves comprises an aerial system for directing such waves to at least one target located at a distance D and for receiving the waves reflected from said target, a mixer circuit having a first input for receiving a local signal, a second input for receiving the reflected signal received by the aerial system, and an output for producing information about the distance D, a frequency-modulated (FM) wave generator, a change-over device cooperating with a control circuit for temporarily connecting the FM wave aerial system to the generator, while the first input of the mixer circuit receives a signal derived from the output signal of the FM wave generator by means of a coupler. The control circuit comprises means for connecting the aerial system to the output of the FM wave generator during one of equal fixed time durations selected in a pseudo-random manner within a time interval of a fixed duration.

Abstract: A method for determining the azimuth .alpha. of a transponder relative to a radar system which transmits a frequency F varying linearly with time. The system comprises two receiving antennas disposed at a distance d from each other and produces two beat signals Fb.sub.1 and Fb.sub.2, formed by mixing the transmitted wave with each of the two echo waves received from the transponder. The phase shift .phi. between Fb.sub.1 and Fb.sub.2 at a first time t, and frequency f, and the phase shift .phi.'.sub.o at a second time t.sub.2 and frequency f.sub.2 is measured, and the overall phase shift .phi. between Fb.sub.1 and Fb.sub.2 is calculated. The value of .alpha. is calculated from the values F.sub.1, d and .phi..

Abstract: 44A radar arrangement (1) suitable for measuring the horizontal velocity v of an aircraft relative to the ground (2) comprises an high-frequency signal generator (10) including a transmitting aerial (9), a receiver including two aerials (12, 11) spaced a distance d apart along a line in the direction of the velocity to be measured and respective mixers (30, 31) and filters (32, 33), and a correlator (15) which determines the value (.tau.=d/v) of the delay of the signals received at the rearmost aerial (11) relative to those received at the foremost (12) for which the correlation is a maximum. The signal generator (10) generates two linearly frequency-modulated waves (E2, E1) and is controlled by the correlator (15) so that the interval between E2 and E1 equals .tau.. The height H of the aircraft can also easily be determined, being directly proportional to the beat frequency at the output of the filters (32, 33).

Abstract: A system for determining the range H to an object and the relative velocity v of the object, including means for generating first and second high-frequency signals, transmitting, receiving and mixing the received high-frequency signal with the high-frequency signal transmitted for generating first and second beat signals, and an arithmetic unit determining in an iterative manner from the point at which one of the two beat frequencies has the lowest value, the value of H and the value of v.

Abstract: A FM-CW radar distance measuring apparatus, comprising a feedback loop having a high-frequency signal generator, a mixer device producing a beat signal between the transmitted wave and the received wave, a frequency discriminator, an integrator and a modulator which produces a sawtooth voltage for controlling the generator. The duration of the sawtooth is directly proportional to the distance to be measured. To improve the linearity of the signal to be transmitted a second (digital) feedback loop is provided, connected between the discriminator output and the modulator input and comprising the cascade arrangement of a threshold device, an adder, a store (and a digital-to-analog) converter. A distribution element connects the modulator to the store.

Abstract: The disclosed system is intended to supply angular and range data regarding the position of an object to be located in a reference system. The system comprises an interrogator which transmits a linearly frequency-modulated signal to a transponder disposed on the object. The transponder is provided with means for shifting the frequency of the received signal in one direction by a predetermined amount characteristic of that transponder and means for retransmitting the received signal. The interrogator further includes a pair of receiving antennas whose signals are used for forming beat signals with the transmitted signal. The interrogator is also provided with means for shifting the frequency of the beat signals in the other direction by the same amount. At least one of the shifted beat signals is applied to a frequency discriminator whose output signal is utilized for controlling the slope of the modulation signal in order to keep the frequency of the shifted beat signal constant.