Page 54 - Antennas for Base Stations in Wireless Communications

Fundamentals of Antennas 27

within a large dynamic range of power levels in order not to introduce
measurement errors. When measuring, the antenna under test is excited
by a given power level at two close fundamental frequencies, and the
fundamental and 3rd order intermodulation components are measured
and recorded on the receiving side. The operation is repeated for different
input power levels, and finally it gives two curves—one is the received
power level of the fundamental component versus input power, and the
other one is the received power level of the 3rd order intermodulation
component versus input power. From the two curves, we can obtain the
3rd order intercept point, which indicates the power dynamic range of
the antenna under test for linear operation. Figure 1.17 shows an exam-
ple of measurement systems for intermodulation in an anechoic chamber,
which is installed at the City University of Hong Kong, SAR, China.

AUT

Figure 1.17 Example of measurement systems for passive inter-
modulation (Facility is available at the State Key Laboratory of
Millimeter Waves at City University of Hong Kong.)