Communications: directive radio wave systems and devices (e.g. – With particular circuit – For correlation
Patent
1997-02-10
1998-08-25
Sotomayor, John B.
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
For correlation
342135, 342145, 342203, G01S 1353, G01S 7292
Patent
active
057987297
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a pulsed radar apparatus, comprising a transmitter unit for the generation and transmission of transmitter pulses provided with a modulation that enables pulse compression upon reception, a receiver unit for the reception of reflected transmitter pulses, a correlator for compressing the received transmitter pulses, and a blanking circuit for blanking received pulses not provided with the modulation.
The invention furthermore relates to a method for suppressing interference pulses in a radar apparatus.
2. Discussion of the Background
Such a radar apparatus is known from patent application EP-A 0 408 112. In this known radar apparatus the amplitude of a received pulse before the correlator is compared with the amplitude after the correlator. If the pulse during its path through the correlator does not show a significant increase in amplitude, it is assumed to be an interference pulse, as a result of which the blanking circuit is activated.
A drawback of this known radar apparatus is that the interference pulse enters the correlator. A common misconception is that a decorrelator will correctly decorrelate an interference pulse, i.e. a pulse not provided with the correct modulation, in which process the amplitude will decrease to a level that is comparable to the thermal noise level inherent in the radar receiver. Particularly in case of state-of-the-art radar equipment designed for the detection of targets with extremely small radar cross-sections, such as missiles, the detection criteria are refined to such an extent that a decorrelated interference pulse is not acceptable. The decorrelated interference pulse may even entail greater drawbacks than the original interference pulse, because the decorrelation process causes the duration of the pulse to be extended considerably, as a result of which the radar apparatus is eclipsed for a longer period.
SUMMARY OF THE INVENTION
The radar apparatus according to the invention is therefore characterised in that the blanking circuit is provided with means for suppressing the pulses not provided with the modulation before these can enter the correlator.
An advantageous embodiment of the radar apparatus according to the invention is based on the fact that the modulation is accurately known and is characterised in that the means at least comprise a first filter designed for producing a first output signal during a first part of a received transmitter pulse and a second filter designed for producing a second output signal during a second part of a received transmitter pulse, the first part and the second part being at least substantially disjunct, and in that the blanking circuit is activated if the first output signal and the second output signal are produced at least substantially simultaneously.
In case the modulation is a linear chirp, the first filter and the second filter can be advantageously implemented as bandpass filters. This for instance enables the first filter to be tuned to the first half of the linear chirp and the second filter to the second half of the linear chirp. This results in a simple system of filters that is by nature disjunct for the linear chirp.
For comparing the output signals of the first filter and the second filter, the output signals can be advantageously applied to a first and a second modulus-determining element respectively. In case of analogue signals, the obvious solution is to use a detector circuit, well-known in the art. In case of complex digital signals, an equally well-known modulus circuit may be used. If the operations are performed in a computer memory, the modulus is determined on the basis of a number of known arithmetical operations.
Subsequent to the determination of the modulus it is possible, for reducing the susceptibility to short interference peaks, to incorporate a first smoothing filter and a second smoothing filter after the first modulus-determining element and the second modulus-determining element respectively.
A further advantag
REFERENCES:
patent: Re33816 (1992-02-01), Nagasaki et al.
patent: 3858208 (1974-12-01), Parke et al.
patent: 4700327 (1987-10-01), Hilton
patent: 5539407 (1996-07-01), Scholz
patent: 5668828 (1997-09-01), Sanderford, Jr. et al.
Hollandse Signaalapparaten B.V.
Sotomayor John B.
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