Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Patent
1980-12-23
1983-05-24
Tubbesing, T. H.
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
343 172R, G01S 1324, G01S 1352
Patent
active
043852980
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a MTI-filter included in the receiver of a tracking radar for suppressing clutter when receiving echo pulses from a target intended to be tracked by the radar.
BACKGROUND OF THE INVENTION
In the U.S. patent application Ser. No. 06/227,081 a method and apparatus in a tracking radar is described for transmitting radar pulses whose carrier frequency varies from one transmitted pulse to the next following, a number M of such pulses forming a series of pulses having the time length 1/f.sub.FRF, where f.sub.FRF is, with respect to the target range R, a chosen quantity. The series of pulses is transmitted sequentially, the number M of carrier frequencies and the order of these being the same from one series to the next following provided that the target range does not exceed a certain value Rk, i.e. R.ltoreq.Rk. If the target range R becomes greater than Rk, a new (and lower) value of the frequency f.sub.FRF is chosen, so that continuously an unambigous determination of the target range can be obtained.
It is previously known in a pulse Doppler radar to suppress clutter, i.e. disturbing echoes from, for example, ground, sea or precipitation by providing so called MTI-filters (Moving Target Indication), see, for example U.S. Pat. No. 3,786,509. Such a filter consists of one or more delay links each with a delay 1/f.sub.PRF, where f.sub.PRF is the pulse repetition frequency of the radar, the signals from the delay links being tapped and added to form an output signal which constitutes the filtered input signal. Such filters show a periodic filter characteristic with a pass band between the so called blind speeds, i.e. for the speeds at which a certain suppression is obtained in addition to the desired suppression of the clutter. The blind speeds then coincide with the speeds whose resulting multiples of Doppler frequency constitute the pulse repetition frequency f.sub.PRF.
SUMMARY OF THE INVENTION
It is an object of a tracking radar to be able to combine MTI-filtering and frequency change from pulse to pulse according to the method described in the above mentioned U.S. patent application. By means of the filter according to the present invention applied in a search radar of the kind mentioned in the introduction, an MTI-function combined with such a frequency change be attained. Furthermore, the filter response, i.e. the filter amplification as a function of the Doppler frequency of received target echoes, can be adapted to the velocity of the followed target so that the filter response becomes periodic with a period corresponding to the frequency repetition frequency f.sub.FRF of the transmitted series of radar pulses and not to the pulse repetition frequency f.sub.PRF of the radar.
An object of the present invention is thus to provide an MTI-function for a tracking radar in which the carrier frequency of the transmitted radar pulses changes from one pulse to another but in which the same carrier frequency returns from one pulse series to another, a filtering of incoming disturbing echoes being attained at the same time as the sensitivity when receiving the target echo is optimized.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully described with reference to the accompanying drawings in which:
FIG. 1 shows a block diagram of the transmitter-receiver part of a tracking radar;
FIG. 2 shows a block diagram of an MTI-filter included in the receiver part according to FIG. 1,
FIG. 3 shows a diagram of the characteristic of the filter according to the invention,
FIG. 4 shows closely the design of certain blocks in the diagram according to FIG. 1.
PREFERRED EMBODIMENTS
The transmitter-receiver units of a tracking radar using the method mentioned in the introduction are shown in FIG. 1. To the radar antenna A a duplexer SM is connected to transmit radar pulses from a transmitter unit S with the frequency m.multidot.f.nu.+f.sub.MF, where m.multidot.f.nu. indicates the carrier frequency of the radar pulses (.nu.=const., m=1, 2, . . . M) and f.sub.
REFERENCES:
patent: 3383686 (1968-05-01), Davis et al.
patent: 3725926 (1973-04-01), Ares
patent: 3883871 (1975-05-01), Moore
patent: 3991417 (1976-11-01), Levine
patent: 4117538 (1978-09-01), Shrader et al.
patent: 4155088 (1979-05-01), Taylor, Jr. et al.
patent: 4206463 (1980-06-01), Glasgow
Josefsson Lars G.
Oderland Karl-Erik I.
Winnberg Jan-Olov
Telefonaktiebolaget L M Ericsson
Tubbesing T. H.
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