CAUTION
Maintain prescribed safe distance when standing in front of radiating
antenna.
Never expose eyes or any part of the body to an unterminated wave
guide.
EXAMPLE
The following is typical data for the airborne weather radar.
Antenna Diameter:18 inches = 45.6 cm
Transmitter Frequency:9375 +30 MHz
Wave Length:3.2 cm
Pulse Length:2.5 microseconds (search)
Pulse Repetition:200 Hz
Peak Power:10 kilowatts
Average Power:5 watts (search)
Antenna Gain:1250 (31 dB)
Calculations
(1)Distance (Ri) to the near field/far field intersection
Ri = Gλ
8π
Ri = (1250 x 0.032)
8π
=1.6 meters = 5.25 feet
(2)Distance (Rs) to 1 mw/cm
2
safe limit
= 7.05 meters = 23.1 feet
The distance (Rs) is greater than (Ri), therefore, the minimum safe distance
is 23.1 feet.
π40
GP
Rs =
π40
(1250)(5)
=
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