Radar system using a cell averaging constant false alarm rate device

• US 5,808,579 A
• Filed: 12/20/1996
• Issued: 09/15/1998
• Est. Priority Date: 12/20/1996
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: Northrop Grumman Corporation
• Inventors: Rademacher, Paul E.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/772,668
• Time in Patent Office: 634 Days
• Field of Search: 342/93, 342/95, 342/159, 342/160, 342/162, 342/203
• US Class Current: 342/93
• CPC Class Codes: G01S 7/12 Plan-position indicators, i.e. P.P.I.
• CPC Class Codes: G01S 7/2926 by integration
• CPC Class Codes: G01S 7/295 Means for transforming co-ordinates or for evaluating data, e.g. using computers

Abstract

A cell averaging (CA) constant false alarm rate (CFAR) device for use in a radar system which filters noise and clutter from a signal containing a plurality of range cells. A moving window average calculator (MWAC) calculates a moving window average (MWA) for each range cell in a signal. A central processing unit (CPU) estimates a skew factor of a probability density function (PDF) and calculates an offset factor based on information contained in the signal. A multiplying device multiplies the offset factor by the MWA calculated for each range cell and creates a second signal containing a plurality of range cells. A comparator compares each range cell of the second signal to each corresponding range cell of the original signal, selects a the larger value of the two signals, and creates a third signal which is essentially free of noise and clutter.

Claims

1. A radar system for identifying an object of interest, said radar system comprising:

a transmitter means for producing a first signal;

a duplexer means for receiving and processing signals, where said duplexer means receives said first signal from said transmitter;

an antenna, where said antenna receives said first signal from said duplexer means and transmits said first signal into the atmosphere, receives a second signal reflected by objects present in the atmosphere, and routes said second signal to said duplexer;

a receiving means for receiving said second signal from said duplexer, where said receiving means samples said second signal at defined intervals known as range cells, and develops a third signal;

a cell averaging (CA) constant false alarm rate (CFAR) means for eliminating a clutter component from said third signal and developing a fourth signal, where said CA CFAR means includes

(i) a moving window average calculator (MWAC),

(ii) a central processing unit (CPU) for estimating a skew factor of a probability density function (PDF) and calculating an offset factor based on information contained in said third signal,

(iii) a multiplying unit, and

(vi) a comparator; and

a display means for receiving and displaying said fourth signal.

2. A radar system as defined in claim 1, wherein (i) said MWAC calculates a moving window average (MWA) for each range cell in said third signal, (ii) said offset factor is calculated by said CPU for each range cell based on said estimated skew factor, (iii) said multiplying unit multiplies said offset factor by said MWA calculated for each range cell to create a threshold signal for each range cell, (iv) said threshold signal calculated for each range cell is compared to each range cell in said third signal by said comparator, and (v) said comparator selects the large value of the two signals to create said fourth signal.

3. A cell averaging (CA) constant false alarm rate (CFAR) device for eliminating a clutter component from a signal received by a radar system containing a plurality of range cells, said CA CFAR device comprising:

a moving window average calculator (MWAC) for calculating a moving window average for each range cell in said received signal;

a central processing unit (CPU) for estimating a skew factor of a probability density function (PDF) and calculating an offset factor based on information contained in said received signal;

a multiplying means for multiplying said offset factor by said MWA calculated for each range cell in said received signal to create a second signal containing a plurality of range cells; and

a comparator for comparing each range cell of said second signal to each corresponding range cell of said received signal and selecting a the larger value of the two signals to create a third signal.

4. A method for identifying an object of interest when using a radar system, said method comprising the steps of:

(1) transmitting a first signal into the atmosphere;

(2) receiving a second signal reflected by objects present in the atmosphere; and

,

(3) using a cell averaging (CA) constant false alarm rate (CFAR) normalization technique to estimate a skew factor of probability density function (PDF) and calculate an offset factor M based on information contained in said second signal.

5. A method for identifying an object of interest using a radar system as described in claim 4, wherein step (3) further includes the steps of:

(a) calculating an arithmetic and geometric mean;

(b) calculating a factor r based on said arithmetic and geometric mean;

(c) calculating a skew factor S based on said factor r;

(d) defining a desired false alarm probability (FAP); and

,

(e) calculating said offset factor M based on said skew factor S and said FAP.

6. A method for identifying an object of interest using a radar system as described in claim 5, wherein:

(i) said factor r is defined as follows ##EQU5## (ii) said skew factor S is defined as follows ##EQU6## (iii) said offset M factor is defined as follows ##EQU7##

7. A method for identifying an object of interest using a radar system as described in claim 6, further including the step of calculating a threshold voltage by multiplying said offset factor M by said arithmetic mean.

8. A method for identifying an object of interest using a radar system as described in claim 5, wherein:

(i) said factor r is defined as follows ##EQU8## (ii) said skew factor S is defined as follows ##EQU9## (iii) said offset factor M is defined as follows ##EQU10##

9. A method for identifying an object of interest using a radar system as described in claim 8, further including the step of calculating a threshold voltage by multiplying said offset factor M by said geometric mean.