Constant False Alarm Rate

1. Constant False Alarm Rate
(CFAR)
Presented By:
Umair Saeed

2. Agenda
CAGO-CFAR
OS-CFAR
CASH-CFAR
MAMIS-CFAR

3. What is CFAR?
• Constant false alarm rate (CFAR) detection
refers to a common form of adaptive
algorithm used in radar systems to detect
target returns against a background of noise,
clutter and interference.

4. What is CFAR?
• Constant false alarm rate (CFAR) is a
property of threshold or gain control devices
that maintain an approximately constant
rate of false target detections when the noise,
and/or clutter levels, and/or ECM (electronic
countermeasures) into the detector are
variable.

5. Why Do We Use CFAR?
• CFAR techniques are used in reception and
signal processing to avoid increased false
alarm rates in the presence of jamming,
clutter residue, or other interference sources.

6. CFAR
• The basic feature of CFAR is that the false
alarm probability remains approximately
constant in clutter by a threshold, riding a
definite value above clutter. Targets with an
echo power exceeding the threshold level can
still be detected.

7. Efficient CFAR Requirements
• Efficient implementation regarding required
processing power and production costs.
• Low CFAR-loss.
• Accurate fitting of the CFAR threshold to the
clutter scenario.
• The CFAR threshold must pass point targets
and extended targets.
• Closely spaced targets must not mask each
other.

8. CAGO-CFAR

9. CAGO-CFAR
• The CAGO-CFAR (Cell Averaging Greatest Of-)
comprises essentially a shift register consisting
of two sub-registers, each containing L storage
cells. Between the sub-registers, the so-called
cell under test (CUT) is located. Each sub-
register has its own adding circuit.(MAX) is use
for adding purpose.

10. CAGO-CFAR continue…
• Using a multiplicative factor α for linear
processing or an additive factor β for
processing with a LOG-amplifier, the threshold
value (TV) is calculated. Finally, the amplitude
of the signal under test (SUT) is compared
with the threshold value to decide whether
the SUT belongs to a target or not.

11. Advantages of CAGO-CFAR
• Require little processing power.
• Having low CFAR loss.

12. Disadvantages of CAGO-CFAR
• Ineffective thresholding.
• Closely spaced targets can mask each other.
• MAX-process, the CAGO threshold cannot
immediately follow an abrupt rise or fall in
clutter level.

13. OS-CFAR

14. OS-CFAR
• The OS-CFAR (Ordered Statistic) comprises a shift
register containing “A” storage cells, plus the CUT.
• A sorting algorithm arranges the amplitudes of
the storage cells in order of decreasing
magnitude.
• In a rank-selection process, the “r-th” largest
amplitude is chosen as a representative of the
clutter.
• The TV is calculated using a multiplicative α or
additive factor β as described for the CAGO-CFAR
above. Target detection is accomplished by
comparing the SUT with the TV.

15. Advantage of OS-CFAR
• In contrast to the CAGO-CFAR, the OS-CFAR
has the advantage of effective threshold
formation.
Disadvantage of OS-CFAR
• The major disadvantage of the OS-CFAR is the
high processing power required for
performing the sorting algorithm.

16. CASH-CFAR

17. CASH-CFAR
• The CASH-CFAR (Cell Averaging Statistic Hofele)
comprises essentially a shift register configured
by “A” sub-registers, each having its own adder
and containing L storage cells.
• By means of a special maximum-minimum
process a clutter-representative sum-value Sr, will
be selected from the “A” sum-values S1 to SA.
• The threshold value is then calculated using a
multiplicative (α/L) and/or additive (β/L) factor.
• Special maximum-minimum circuit block
interference.

18. Advantages of CASH-CFAR
• CASH-CFAR avoids mutual masking of targets.
• In clutter level with almost no time
displacement.
• CASHCFAR requires much less processing
power than the OS-CFAR with its rank-
selection method.

19. MAMIS-CFAR

20. MAMIS-CFAR
• The MAMIS-CFAR (Maximum Minimum Statistic)
is essentially the same as the CASHCFAR,
• except that the special maximum-minimum
circuit M replaces the adders of the
• CASH-CFAR. The characteristics of the MAMIS-
CFAR are quite similar to those of the
• CASH-CFAR. For the CFAR-handling of block
interference and of point- and extended targets.

21. THANKS