Page 85 - Radar Technology Encyclopedia

channel, radar chart, Blake 75

through the interaction of electromagnetic waves radiated by viewpoint, to optimize performance of the radar, and to sim-
the antenna with the radar target. The information is trans- plify estimation of radar characteristics during preliminary
ported by an electromagnetic field (space-time process) to the design and experimentation. IAM
radar receiver, in which it is transformed into a radar signal Ref.: Tuchkov (1985), p. 11.
(time process).
sum channel (see MONOPULSE).
The radar channel may be analyzed through a description
of the transformation of the signal characteristics along the CHART
transmitter-target-receiver path, using quantitative estimates
A Blake chart is the pulsed-radar-range-calculation work-
in various information metrics.
sheet displaying the terms and basic steps for radar range
Such an information-based description of the radar chan-
equation calculations (Fig. C15). It is based on logarithmic-
nel is concerned not with the signals themselves, but with
decibel form of the range equation and was devised by L. V.
their content: the quantity and quality of the information, giv-
Blake in 1969 for manual computation. Today, for computer-
ing a quantitative estimate in information metrics of the effec-
aided computation, the output form of range calculation
tiveness of the operation of the radar as a whole and, if
worksheet can differ from Blake’s original form but typically
possible, its components. is also termed Blake chart. SAL
An information-based description makes it possible to
examine the functioning of the radar from the most general Ref.: Blake (1980), p. 383.
.
PULSE-RADAR RANGE CALCULATION WORKSHEET
Detection probability P d = False-alarm probability P fa = Target case: Hits n =
Radar antenna height h = m Target elevation angle q t = deg
r
A. Computation of T s : B. Range Factors C. Decibel Values Plus (+) Minus (- )
T = T + T + L T P or P (W) 10 log P (dBW)
a
r
s
r e
av
t
(a) Compute T a t or t (s) 10 log t (dBs)
f
For T = T = 290K, T = 36K G t G t(dB)
g
ta
g
T = (0.876T ¢ - G G
254) + 290K
a a r r(dB)
2
L a(dB) : L a : s (m ) 10 log (dBm )
2
s
2
T ¢ = K l (m) 20 log l (dBm )
a
T a : K T s (K) - 10 log T (dBK)
s
(b) Compute T = T (L - 1) D - D (dB)
r
tr
r
L r(dB ): L r : M - M (db )
T : r K L p - L p(dB )
(c) Compute T = T (F - 1) L x - L x(dB)
0
n
e
F F : L - L
n(dB) n t t(dB)
T e : K L r : Range-equation constant (dBK× s/K) +75.62
L T = K 5. Obtain column totals
r e
(d) Add: T s : K 6. Enter the smaller below the larger
4
7. Subtract to obtain net decibels X = 40 log R km (dBm )
8. Calculate R 0 (km) = antilog (X/40) R 0(km) =
9. F =
Calculate the pattern-propagation factor F = F F
t r
R
10. Multiply R by the pattern-propagation factor to obtain R¢ = ´ F R¢ =
0 0
11. From curves of atmospheric attenuation, determine the loss L a(dB) , corresponding to R¢ . This is L a(dB)(1) =
L a(dB)(1).
12. Find the range factor d 1 = antilog (- L a(dB)(1) /40) d 1 =
13. Multiply R¢ by d 1 . This is a first approximation of range, R . R¢ =
1
14. If R 1 differs appreciably from R¢ , find a new value of L a(dB) corresponding to R 1 . L a(dB)(2) =
15. Find the range increase factor d 2 corresponding to the difference between L a(dB)(1) and d 2 =
L .
a(dB)(2)
16. Multiply R 1 by d to obtain the maximum radar detection range R m in km R m(km) =
2
Figure C15 Blake chart for pulse-radar-range calculation, modified as in Barton, 1988, Fig. 1.2.4, p. 21.