Design of Antennas for Handheld DVB-H ... - Lunds tekniska högskola

Figure 5.22. Radiation pattern for Switched monopole 2, frequency=630 MHz,
Theta=0°-350°, Phi=90°, A=Theta polarization, B=Phi polarization.
5.1.4 Measurement reliability
Since the anechoic chamber, where the measurements were made, was
constructed to measure frequencies above 700 MHz the correctness of the
measurements made can be discussed.
The dipole antennas that were used as reference antennas were not built with very
high precision and will therefore contribute to somewhat higher uncertainty in the
measurements. The reference dipole antennas have higher losses than an ideal
dipole, therefore the maximum measured value for the reference antennas were
estimated to 1.6 dBi instead of 2.15 dBi.
The moderating cones in the chamber are constructed to moderate frequencies
down to 500 MHz, however it cannot be certain that no standing waves appear in
the chamber when frequencies below 700 MHz are measured.
When antennas are measured in a near field chamber as the one used, the distance
between the probes and the antenna under test should be at least three times the
wavelength of the frequencies measured. This is to lower the interaction between
the probes and the antenna. This means that the distance between the probes and
the antenna under test should be close to two meters when measuring on 470 MHz
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