Communications: directive radio wave systems and devices (e.g. – Radar ew – Eccm
Patent
1997-01-13
1998-08-04
Sotomayor, John B.
Communications: directive radio wave systems and devices (e.g.,
Radar ew
Eccm
342102, G01S 736
Patent
active
057900671
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a radar apparatus for the coherent transmission and reception of radar pulses, provided with a transmitting unit having a transmit phase shifter, a receiving unit and a video processor for the processing of received radar echoes.
A radar apparatus of this kind is known from FR-A 2.455.288. In this known apparatus the phase shifter is used for phase shifting an individual radar pulse a number of times during that pulse in a well defined manner. Received radar echo pulses are autocorrelated with the transmitted pulse, resulting in a compressed echo pulse with an increased range resolution and an increased signal to noise ratio.
The present invention does not aim at compressing the echo pulses but at generating misleading information for a repeater jammer that might be active. A repeater jammer is adapted for deliberately generating interference with a jamming transmitter that is capable of producing a replica of a received radar pulse. For that purpose the repeater jammer stores the first received pulse of a burst of radar pulses in a memory and subsequently uses this stored pulse for the generation of a burst of simulated radar echo pulses representing a simulated target, as a result of which the video processor is incapable of distinguishing the simulated target from a true target. By subsequently manipulating the simulated radar pulses, the jammer may constitute a serious threat to the operational effectiveness of the radar apparatus.
The present invention intends to make a repeater jammer less effective and is characterised in that the transmitting unit is adapted for transmitting bursts of radar pulses, that the transmit phase shifter is adapted for phase shifting individual transmitted radar pulses within a burst with a selected phase shift, that the receiving unit is provided with a receive phase shifter, for providing the received echo of a radar pulse with a reverse of the phase shift selected for that radar pulse on transmission.
Since the selected phase shift is completely cancelled in the received radar pulses, the coherence remains unaffected and the overall effectiveness of the radar apparatus remains unchanged. On the contrary, received simulated radar pulses, derived from the first pulse in a burst have a phase shift that corresponds to the inverted selected phase shift, because the receiving unit in fact compensates for a non-applied selected phase shift.
A first embodiment of the radar apparatus is characterised in that the video processor is provided with a correlator for correlating the phase of radar pulses in a received burst with the phase in a transmitted burst, for generating a signal which indicates whether a repeater jammer is operational, which signal can subsequently be used to prevent a radar track from being based on the simulated target.
Repeater jammers of greater sophistication have means for providing transmissions with a pulse-to-pulse increasing or decreasing phase, on the basis of the first pulse in a burst, which means enable the simulation of a target having a certain velocity. The use of a correlator will then no longer be sufficient. A favourable embodiment of the invention is thereto characterised in that the video processor is provided with a Doppler filterbank for determining velocities of possible targets and in that the phase shift realizes a selected distribution of received repeater jammer pulses over the Doppler filterbank outputs.
In a first realization of this embodiment, the phase shift is selected for obtaining an at least substantially even distribution of received repeater jammer pulses over the Doppler filterbank outputs. The received jammer signals are in a manner of speaking spread over the Doppler domain, after which real targets may be searched by means of a threshold circuit connected to the Doppler filterbank outputs.
In a second realization of this embodiment, the phase shift is selected for at least substantially routing of received repeater jammer pulses to a previously determined Doppler filterbank output. A preferabl
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Scholz John Arthur
Van Ommeren Marinus Josephus Servatius
Hollandse Signaalapparaten B.V.
Sotomayor John B.
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