Page 180 - Maxwell House

160 Chapter 3

The basic antenna parameter measurements are quite simple. The antenna under test is installed
on the rotation positioner like seen in Figure 3.4.7. The test
positioner must provide the high precision rotation in single or
up to three orthogonal angular axes that allows measuring the
3D distribution of radiated or received by antenna power called
antenna radiation pattern. Radiation patterns can be displayed
in a rectangular or polar format as functions of the spherical
coordinates’ φ and θ as shown in Figure 3.4.8. It is clear that
Figure 3.4.8 3D antenna the antenna test setup displayed in Figure 3.4.6a provides the
pattern data about the receiving pattern.

Meanwhile, according to Lorentz’s reciprocity theorem, the transmit (Tx) and under test
antenna can switch places without any impact on test results. Let us pay a little bit more
attention to this subject refereeing to Figure 3.4.9 that is slight modification of Figure 3.3.11
and is the external to in Figure 3.4.9a or vice versa in Figure 3.4.9b. Assuming that the
1
2
red test antenna on positioner is connected to power source radiates and the black receiving
antenna is stationary as shown in Figure 3.4.9a. It was assumed that the antennas are far away
from each other that it is possible to neglect the interaction between antennas near-fields.

Figure 3.4.9 Transmit and receiving antenna reciprocity illustration

Then according to (3.107)

(φ, θ ) = ( ) (3.110)
1
1
21 1
while in the setup 3.4.9b
(φ, θ ) = ( ) (3.111)
2
12 2
2
Taking into account (3.108) we obtain

(φ, θ )=[ ( ) ( )⁄ ] (φ, θ ) = (φ, θ ) (3.112)
2 2 2 1 1 1 1
Evidently, the constant is defined by the power of sources connected to the rotated antennas
and independent on the angular antenna positions. Therefore, the antenna pattern shape would
not depend on test mode.