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210 ANTENNA BASICS
2
= −10 log (1 − | | ) [dB] (5.15)
10
Figure 5.2.3 illustrates the relation (5.15). Additional parameter characterizing the reflection
loss is the Voltage Standing Wave Ratio (VSWR) defined as
1+| |
= (5.16)
1−| |
Figure 5.2.3 Reflection loss vs. reflection coefficient
Figure 5.2.4 Reflection loss vs. voltage standing wave ratio
A visual mapping the reflection loss and VSWR is shown in Figure 5.2.4. The smaller VSWR
is, the more power is delivered to the antenna. The standard requirement is VSWR < 1.5 – 2
that corresponds to ≤ 0.5 dB.
5.2.4 Antenna Quality Factor (Q-factor), Bandpass and Radiation Efficiency
The antenna quality factor Q is defined almost in the same way as it is for cavity resonators
(see (3.68)). It is the quotient between the power ℑ( ) stored in the reactive field and the
