US 6,380,887 B1Granted

Method of reducing clutter and mutual interference in a coherent doppler radar system

AssigneeChung-Shan Institute of Science and Technology

InventorTain-Wen Suen

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Abstract

A method is proposed for use on a coherent Doppler radar system for the purpose of reducing the clutter and mutual interference in the coherent Doppler radar system. The echoed radar signal from the target object is converted into a Range-Doppler Domain output signal. If the Range-Doppler Domain output signal indicates the presence of mutual interference, a Crisscrossing CFAR method is selected to compute for the CFAR back-ground value; otherwise an Area CFAR method is selected. A target-detection logic circuit is then used to obtain the radar information about the target object. By the proposed method, the output signal of the target-detection logic circuit is substantially free from clutter and mutual interference, which is further converted into a radar display signal to drive a radar display unit to display the location and velocity of the target object.

Claims27

Dependent claims

A radar system for detecting a target object, which comprises:

a transmitter for generating a pulsed radar signal composed of a series of pulses spaced at a predetermined pulse repetition interval PRI;
an antenna for emitting the pulsed radar signal from the transmitter into the ether, and in the event of the emitted radar signal meets the target object, picking up the echoed radar signal;
a receiver for receiving the echoed radar signal picked up by the antenna and performing a preliminary signal processing procedure on the echoed radar signal;
an analog processor, coupled to the receiver, for processing the output signal of the receiver and thereby generating a video frequency signal;
a digital signal processor coupled to the analog processor, which is capable of digitally filtering out the clutter and mutual interference in the output video frequency signal from the analog processor to thereby generate a radar display signal comprising:
a clutter canceller, receiving the output signal of the analog processor, for filtering out the clutter in the output signal of the analog processor;
an integration processor, receiving the output signal of the clutter canceller, for converting the output signal of the clutter canceller into a Range-Doppler Domain representation having a number of range cells and a number of Doppler cells;
a Mutual Interference Detector (MID) unit, coupled to the integration processor, for detecting whether the output signal from the integration processor contains mutual interference and thereby produce an output signal indicative of the detected result;
a Constant False Alarm Ratio (CFAR) selector, coupled to the MID unit, which is capable of selecting a suited method for the computation of CFAR background value based on the output signal of the MID;
a CFAR detector, coupled to the integration processor and the CFAR selector, for generating an output signal indicative of the CFAR background value through the use of the method selected by the CFAR selector;
a target-detection logic circuit, coupled to the CFAR detector, for converting the output signal of the CFAR detector into an output signal indicative of the radar information about the target object and which is substantially free of clutter and mutual interference;
an Range Ambiguous Resolver (RAR), coupled to the target detection circuit, for performing a range ambiguous resolving process on the output signal of the target detection circuit;
a digital scanning converter coupled to the RAR, whose output signal serving as the radar display signal;
and
a radar display unit, which is driven by the radar display signal from the digital signal processor, for displaying the radar information about the target object.

12 more elements

A method for use on a coherent Doppler radar system utilizing a pulsed radar signal for detecting the radar information about a target object for the purpose of reducing the mutual interference in the echoed radar signal reflected from the target object;

the method comprising the steps of:
performing a coherent processing procedure on the echoed radar signal to thereby convert the echoed radar signal into a Range-Doppler Domain representation consisting of a number of range cells and a number of Doppler cells;
from the Range-Doppler Domain, determining a Mutual Interference Detector (MID) Range Crossing value and a MID Doppler Crossing value;
from the MID Range Crossing value and the MID Doppler Crossing value, computing the value of the MID Range Crossing Repeat Interval and the value of the MID Doppler Crossing Repeat Interval;
checking whether the MID Range Crossing Repeat Interval and the MID Doppler Crossing Repeat Interval are regular,
if YES, performing a Crisscrossing Constant False Alarm Ratio (CFAR) method to compute for the value of CFAR background;
selecting a Cell Under Test (CUT) from the Range-Doppler Domain;
computing the amplitude of the selected CUT against the CFAR background;
specifying a minimum threshold, a CFAR background multiple, and a Pulse Repetition Frequencies (PRF) Index;
computing for the threshold of the selected CUT, where the threshold of the selected CUT is equal to the multiplication of the CFAR background value of the selected CUT by the CFAR background multiple;
checking whether the amplitude of the selected CUT is greater than or equal to the threshold of the selected CUT and also greater than the minimum threshold;
if YES, indicating that the selected CUT corresponds to the target object and outputting the amplitude of the selected CUT together with the PRF Index to a radar display unit;
and
based on the amplitude of the selected CUT and the PRF Index, displaying the location and velocity of the target object on the radar display unit.

11 more elements

A radar system for detecting a target object, which comprises:

a transmitter for generating a pulsed radar signal composed of a series of pulses spaced at a predetermined pulse repetition interval PRI;
an antenna for emitting the pulsed radar signal from the transmitter into the ether, and in the event of the emitted radar signal meets the target object, picking up the echoed radar signal;
a receiver for receiving the echoed radar signal picked up by the antenna and performing a preliminary signal processing procedure on the echoed radar signal;
an analog processor, coupled to the receiver, for processing the output signal of the receiver and thereby generating a video frequency signal;
a digital signal processor coupled to the analog processor for removing clutter from the signal, converting the signal into a plurality of range cells, using a nail pattern in the Range-Doppler domain to remove interference, determining if a selected cell corresponds to a target object, and outputting information regarding a cell corresponding to the target object along with the pulse repetition frequency index and the location and velocity of the target object;
and
a radar display unit, which is driven by the radar display signal from the digital signal processor, for displaying the radar information about the target object.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/520,417Filed 8 Mar 2000
Granted: 30 Apr 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

G01S 13/532
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…:…
G01S 7/2923
Extracting wanted echo-signals: based on data belonging to a number of consecutive radar periods
G01S 13/5246
Based upon the phase or frequency shift resulting from movement of objects, with reference to the transmitted signals, e.g. coherent MTi: post…
G01S 7/288
Receivers: coherent receivers