Abstract: A radar transmitter in which a pseudo-random sequence of pulses are transmitted, each at a different frequency. Prior to the return of the first pulse, a receiver is retuned to the first transmit frequency, then the transmitter is retuned to the second transmit frequency and so on. The return pulses are integrated coherently across the sets at a each frequency to achieve the highest signal level. The pulses are integrated noncoherently within a set over all the frequencies transmitted to improve the signal-to-noise ratio.The technique of the present invention requires accurate knowledge of the range to the target. In a specific multi-line embodiment, the range calculation is provided by the centerline carrier frequency operating at a medium pulse repetition (prf) frequency. The retuning is then performed with the sidebands operating at a low prf.

Abstract: A transmitting and receiving part of a pulse Doppler radar, in which the transmitting oscillator, by frequency shifting, is at the same time used as a local (reception) oscillator, and the intermediate-frequency reference frequency is generated coherently with respect to the pulse repetition frequency. Since only one high-frequency oscillator is required, the quality of which does not have to meet very high requirements, a low-price pulse Doppler radar can be implemented.

Abstract: A pulse Doppler radar altimeter designed to resolve the ambiguous range problem associated with the use of a pulse repetition interval, which is less than the aircraft altitude, includes a radar transmitter configured to transmit first and second series of pulses where the first series has a pulse repetition interval slightly different from the pulse repetition interval of the second series. At a time when the first series is being transmitted, the receiver electronics including a range gate and a tracker searches for ground returns and positions the range gate in time coincidence with the detected ground return. Control then shifts so that the second series of pulses is transmitted and a determination is made whether overlap of the range gate with the ground return from the second series corresponds to the same altitude as when the first series was involved.

Abstract: A multipurpose system provides radar surveillance for air traffic control purposes. The system includes four separate active phased-array antennas, each with .+-.45.degree. coverage in azimuth, from 0.degree. to 60.degree. in elevation. Each antenna element of each phased-array antenna is coupled by a low-loss path to the solid-state amplifier associated with a transmit-receive (TR) module. Each antenna produces a sequence of pencil beams, which requires less transmitted power from the TR modules than a fan beam, but requires more time because the pencil beam must be sequenced to cover the same volume as the fan beam. In order to scan the volume in a short time, the PRF is responsive to the elevation angle of the beam, so higher elevation angles use a higher PRF. Low elevation angle beams receive long transmitter pulses for high power, and pulse compression is used to restore range resolution, but the long pulse results in a large minimum range within which targets cannot be detected.

Abstract: A multipurpose system provides radar surveillance for air traffic control purposes. The system includes four separate active phased-array antennas, each with .+-.45.degree. coverage in azimuth, from 0.degree. to 60.degree. in elevation. Each antenna element of each phased-array antenna is coupled by a low-loss path to the solid-state amplifier associated with a transmit-receive (TR) module. Each antenna produces a sequence of pencil beams, which requires less transmitted power from the TR modules than a fan beam, but requires more time because the pencil beam must be sequenced to cover the same volume as the fan beam. In order to scan the volume in a short time, the PRF is responsive to the elevation angle of the beam, so higher elevation angles use a higher PRF. Low elevation angle beams receive long transmitter pulses for high power, and pulse compression is used to restore range resolution, but the long pulse results in a large minimum range within which targets cannot be detected.

Abstract: A radar apparatus which employs a pulse train containing an alternating sequence of first and second groups of pulses. The first group comprises a plurality of identical long pulses and the second group comprises a plurality of identical short pulses. The receiver has a single channel, the processing in which is successively adapted for the pulse returns of a group at any one time.

Abstract: A synthetic aperture radar assembly (1) locatable on a satellite (2) for radar imaging of a planet surface (3) in swaths, including means (8) for transmitting pulses (4) of electromagnetic radiation towards the planet surface (3) to be imaged, means (8) for receiving echoes of said pulses (4) returned by said planet surface (3), means for creating an image of a swath (5) of said planet surface (3) from said returned echoes and means for randomly varying the frequency of transmission of said pulses (4) to increase the width (11) of swath (5) imagable.

Abstract: A radar system for determining first time around targets from multiple time around targets using two radar pulse trains of different pulse repetition intervals and thresholding means. Echos from pulses at each pulse repetition interval being compared to determine first time around targets from subsequent time around targets. The radar system uses thresholding levels to determine an echo and is less prone to problems of coincidence gate clashing with high duty cycles.

Abstract: A method is provided for calculating the unambiguous ranges of a radar target in a radar system employing multiple PRFs. The radar system provides digitized data items indicative of return signals in each of a plurality of range intervals for each PRF. A base PRF is selected and a range interval containing a target return signal is selected therefrom. This range interval is correlated with particular range intervals of the remining PRFs to find specific target return signals therefrom which satisfy a first predetermined relationship. This relationship generally provides that a target is identified if a preselected number of correlated range intervals of all PRFs have target return signals therein. If this relationship is satisfied, the target range is calculated from a range equation.

Abstract: A device for removing ambiguities in the range and speed at the output of a Doppler-type radar in which all possible sets (p.sub.1, q.sub.1) and (p.sub.2, q.sub.2) corresponding to echoes at different repetition frequencies are stored in a first memory, p.sub.1 and p.sub.2 representing the number of the range quantum from which an echo signal is received and q.sub.1 and q.sub.2 the number of the filter at the output of which an echo signal is maximum. Pairs of signals are supplied in response to a first clock signal together with radar data in a second memory to two calculating circuits which carry out tests to determine of p.sub.1 and p.sub.2 and q.sub.1 and q.sub.2 respectively come from the same target and calculate the true target distance and true Doppler frequency. If both tests are positive the true distance and frequency are stored in a memory. If either is negative the first clock signal is produced to supply a new pair to the respective calculating circuits.

Abstract: A swept-frequency radar system transmits pulses consisting of swept-frequency subpulses of nonuniform duration separated by short nontransmitting periods during which an array antenna is resteered. The pulses reflected from a target are processed by a method including estimating the target ranges, producing a reference signal at the time at which the pulse reflected from the target is expected to return. The reflected pulse is phase detected by means of the reference pulse to produce phase detected signals which include information relating to the error between the actual range and the estimated range. The phase detected signals are Fourier transformed to produce range error information. The nonuniform subpulse durations reduce the magnitude of range sidelobes.

Abstract: A coherent pulse radar is activated successively according to at least two pulse repetition frequencies. These frequencies are of values such that (a) the received signal is ambiguous both with regard to distance and with regard to velocity, and (b) their ratio is reducible to the quotient of two integers which are preferably adjacent and have no common factors. For the frequency analysis, a number of samples is taken which depends upon the pulse repetition frequency, the numbers of samples associated with the two pulse repetition frequencies being, in relation to one another, in the ratio of the two integers. The distance/velocity resolution cell is then invariant with respect to the pulse repetition frequency; this permits removal of the ambiguity concerning mean information items appertaining to a long integration time.

Abstract: This invention relates to a method of and a device for removing range ambiguity in a pulse Doppler radar and to a radar including such a device especially for missile guidance. On tracking operation at a high pulse repetition frequency the method consists in switching the repetition frequency f.sub.R (k) for each time interval .DELTA.t, over a new value f.sub.R (k+1) obtained in a circuit from the measured ambiguous range y(k) and from the ambiguity number n(k), as estimated in a circuit from radar information supplied by the radar, in order to remove eclipsing, to maintain the ambiguity number constant and to estimate the range with a growing accuracy in the course of the tracking operation.

Abstract: A pulse Doppler radar system with variable pulse repetition frequency has a coherent integrator to which the reflected pulses are supplied in order to avoid deterioration of the indication of a moving target given over-the-horizon reception. The coherent integrator subjects the reflected pulses to a simplified vectorial addition by the use of a number of filters. A precondition for the modified coherent integration is a staggering of the pulse repetition periods such that their sums formed over successive pulse repetition periods are constant, and a phase reference for the signal amplitudes is obtained such that the phase difference is equal to zero after every second pulse repetition.

Abstract: The invention relates to a process for adapting the post integration in a switched pulse repetition frequency radar and a circuit implementing this process. For that, the post integration of the detected signals is effected as a function of the signal received from the Doppler filter. For that, switches are used controlled by comparator circuits.The invention is useful in frequency ambiguous coherent Doppler radars using recurrence frequency switching by blocks.

Abstract: An extended depth-of-focus synthetic aperture radar (SAR) system (13) mounted on a moving platform, including a controller (120), pulse timer (83), synthesizer (105) and modulator (17) for varying the pulse rate interval (PRI) and/or the radar carrier frequency of radar pulses produced, in order to establish a radar return which, when conventionally processed, results in a SAR terrain map exhibiting extended depth-of-focus under conditions of platform acceleration. Depth of focus is established by ensuring the establishment of two or three separate, independently selected focal points in a target region of interest.

Abstract: Disclosed is an alien radio ranging transmitter rejection technique utilizing random PRF to eliminate the possibility of lock-on between two coherent R/T units in close proximity. If one, or both, are utilizing the random PRF technique taught herein, the alien signal is rejected utilizing standard noise suppression techniques. The random PRF is selected utilizing noise or angle data computed from the received return signal and is thereafter utilized to designate which one of a set number of PRF delays is utilized on a substantially random basis.

Abstract: An extended depth-of-focus synthetic aperture radar (SAR) system (13) mounted on a moving platform, including a controller (120), pulse timer (83), synthesizer (105) and modulator (17) for varying the pulse rate interval (PRI) and/or the radar carrier frequency of radar pulses produced, in order to establish a radar return which, when conventionally processed, results in a SAR terrain map exhibiting extended depth-of-focus under conditions of platform acceleration. Depth of focus is established by ensuring the establishment of two or three separate, independently selected focal points in a target region of interest.

Abstract: Described is a pulse radar apparatus having a repetition period containing m wobbles. The pulse radar apparatus is provided with: a transmitting and receiving unit (2), whereby the received target echoes are sampled and digitized; an n-point DFT processing unit (3); a threshold circuit (4); and a cluster combiner circuit (5) comprising means to form a cluster covering one single target using the signals obtained from the threshold circuit (4). Due to the wobbles, additional information arises in the DFT spectra. From the range, azimuth, local maximum values of the DFT spectrum and the associated output channel number of the DFT processing unit (3), a classification unit (6) determines whether a target is a multiple-time-around target. The classification unit (6) is also able to determine the target doppler frequency, even if this frequency exceeds the average pulse repetition frequency.