Antenna Frequency Registration

0078-EX-PL-2002 Text Documents

Southwest Research Institute

2002-04-18ELS_55393

In this case, the power output is the "pulsed power" delivered by the pulse generator to the antenna
structure and represents a maximum value for the transmitter. The maximum voltage delivered to the
antenna terminals by the pulse generator is on the order of 300 kV. Assuming a terminal impedance of
50 ohms, this gives a maximum peak power to the antenna terminals of:

Pa =
(3 ⋅10 )
5 2
= 1.8 GW
50
The radiation efficiency of the unit is expected to be quite low since the antenna is excited not with a
sinusoidal signal but rather a pulse. In addition, the matching between the source and antenna has not
been fine-tuned as the transmitter is in its early stages of development. For the source/dipole
combination used, the vendor quotes a maximum peak field value of 300 V/m on boresight at a range of
100 meters. The radiated power, then, can be calculated as:

2
Er
Pr ,max = r2 ΩA,
Z

where, Er is the peak electric field at range, r, and ΩA is the beam solid angle, and Z is the characteristic
impedance of free space, 377 ohms.

The beam solid angle is given by,

4π
ΩA =
D
so that,

2
Er
Pr ,max = 4πr 2
ZD

For the half-wave dipole, directivity D = 1.64 ("worst case"). Solving for the radiated power (effective
radiated power referenced to a λ/2 dipole), we find

Pr ,max = 18.3MW

Document Created: 2002-04-19 13:52:23
Document Modified: 2002-04-19 13:52:23

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