# US 5,708,437 A · Radar apparatus

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- Number: US 5,708,437 A
- Document ID: US5708437A
- Status: Granted
- Kind: A
- Application number: 08/605,066
- Filed: 1996-03-07
- Granted: 1998-01-13
- Earliest claimed: 1993-09-08
- Assignees: Hollandse Signaalapparaten B.V.
- Inventors: Bernard Gellekink
- Web page: https://patentgrep.com/patent/US5708437A

## CPC

- G01S 13/5244: {Adaptive clutter cancellation (specially adapted for airborne MTI, G01S13/5242)}
- G01S 13/24: using frequency agility of carrier wave
- G01S 13/53: performing filtering on a single spectral line and associated with one or more range gates with a phase detector or a frequency mixer to extract the Doppler information, e.g. pulse Doppler radar {(G01S13/5244 takes precedence)}
- G01S 2013/0254: {Active array antenna}
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

A radar apparatus having a phased array antenna with a large number of transmit and receive modules, a control unit and a video processor. The control unit generates a number of pulse bursts per azimuth-elevation direction, all of which shows slight carrier frequency differences. The video processor determines a doppler spectrum and compared successive spectra for each pulse burst. As a result of the frequency differences, clutter does not show much of a shift while targets which are subject to fold-back in the frequency domain will show considerable shift. A threshold based on a mean spectrum therefore enables detection.

## Claims

### Claim 1

Radar apparatus for the detection of high-speed targets, comprising antenna means, transmitter means for the generation, per antenna direction, of at least M bursts of at least N transmitter pulses, with M=2, 3, . . . , N=2, 3, . . . , receiver means for the reception, per transmitter pulse, of a radar echo signal determined per range quant, and a video processor connected to the receiver means, comprising an N-point doppler filterbank for the processing, per burst and per range quant, of the radar echo signals into an N-bin doppler spectrum and a threshold circuit, provided, for each range quant, with N threshold values for the generation of an alarm when crossing of at least one threshold for at least one range quant occurs, characterized in that the threshold circuit comprises a threshold generator for the generation, per range quant, of N threshold values on the basis of P doppler spectra obtained from P successive bursts, with P=2, . . . , M.

### Claim 2 (depends on 1)

Radar apparatus as claimed in claim 1, characterised in that the threshold generator comprises an accumulator for the generation of a mean doppler spectrum on the basis of the P doppler spectra.

### Claim 3 (depends on 2)

Radar apparatus as claimed in claim 2, characterised in that the threshold circuit comprises a summator for increasing the mean doppler spectrum by an additional threshold value determined per doppler frequency in order to obtain a predetermined false-alarm rate.

### Claim 4 (depends on 3)

Radar apparatus as claimed in claim 3, characterised in that a PRF shall be selected for the transmitter pulses such as to enable an unambiguous determination of the target range within a predetermined detection range.

### Claim 5 (depends on 4)

Radar apparatus as claimed in claim 4, characterised in that successive bursts of at least N transmitter pulses have different radar frequencies.

### Claim 6 (depends on 5)

Radar apparatus as claimed in claim 5, characterised in that the radar frequencies have been selected such that, from burst to burst, a doppler frequency not subject to fold-back shifts at most two doppler bins.

### Claim 7 (depends on 6)

Radar apparatus as claimed in claim 6, characterised in that the M bursts have the same PRF.

### Claim 8 (depends on 6)

Radar apparatus as claimed in claim 6, characterised in that the threshold circuit is provided with a comparator circuit for comparing, per doppler frequency, the last-obtained doppler spectrum with the threshold values and an alarm generator for generating an alarm, if at least K out of L successive doppler spectra show at least one threshold crossing, where K=1, 2, . . . , L=1, 2, . . . , K<L<M.

### Claim 9 (depends on 7)

Radar apparatus as claimed in claim 7, characterized in that the threshold circuit is provided with a comparator circuit for comparing, per doppler frequency, the last-obtained doppler spectrum with the threshold values and an alarm generator for generating an alarm, if at least K out of L successive doppler spectra show at least one threshold crossing, where K=1, 2, . . . , L=1, 2, . . . , K<L<M.