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Chapter 5 229

2 2

Margin = 3 − ∆ ⎫

�4 � 4
(5.67)
2
4 4 ∆ ⎬
and > �

⎭
Figure 5.3.3 demonstrates the exemplary
15
image of RCS [dB] data vs. azimuth coordinate
for Douglas A-26 Invader aircraft. The apparent
goal of military tactics and passive electronic
countermeasures is to minimize RCS of aircraft,
ships, submarines, missiles, and satellites
thereby making them less visible to radar, sonar,
etc. Such technology is called low observable or
Figure 5.3.3 Measured RCS vs. simply stealth. One of such stealth approach has
azimuth coordinate been discussed earlier in Section 2.8.1 of Chapter
2 in the example of the cloaking effect.

Expression (5.67) tells us that if the radar range must be doubled, we need to quadruple antenna
gain or increase the peak transmitter power sixteen times (!) with the same antenna gain.
Typically, radar antennas are high-cost and bulky devices of unique design that severely
restricts their sizes or the effective aperture of the radar antenna. According to (5.49)

4
= = (5.68)

2
Therefore, the inequity in (5.67) yields
2
> � 4 ∆ (5.69)

5.3.4 Bistatic Radar Equation
A bistatic radar schematic is shown in 5.3.4 and demonstrates how to use a separate transmit
16
(Tx) and receiving
(Rx) antenna to catch
backscattering signal.
Note that such radar
configurations or more
complex ones with
multiple transmit and
receiving antennas is
an expensive but

Figure 5.3.4 Bistatic radar schematic effective way to detect
stealth targets and
build a passive missile approach warning systems for homeland security, etc. A bistatic radar
17
schematic is shown in 5.3.4 and demonstrates how to use a separate transmit (Tx) and

15 Public Domain Image, source: https://en.wikipedia.org/wiki/Radar_cross-section
16 Public Domain Image, source: http://woof.tistory.com/217
17 Public Domain Image, source: http://www.rfcafe.com/references/electrical/radar_eqn.htm