Question

A transverse electromagnetic wave with circular polarization is received by a dipole antenna due to polarization mismatch. The power transfer efficiency from the wave to the antenna is reduced to about
1. 50%
2. 35.5%
3. 25%
4. 0%

Answer 1

Correct Answer - Option 4 : 0%

The polarization of an antenna is the polarization of the radiated fields produced by an antenna, evaluated in the far-field.

Due to the reciprocity theorem, antennas transmit and receive in exactly the same manner, i.e. a vertically polarized antenna transmits and receives vertically polarized fields.

In general, for two linearly polarized antennas that are rotated from each other by an angle ϕ, the power loss due to this polarization mismatch will be described by the Polarization Loss Factor (PLF):

PLF = cos²ϕ

Observations:

• If both antennas have the same polarization, the angle between their radiated E-fields is zero and there is no power loss due to polarization mismatch.
• If one antenna is vertically polarized and the other is horizontally polarized, the angle is 90 degrees and no power will be transferred and the antenna efficiency will be close to zero.
• A dipole antenna is usually linearly polarized and the given wave is circularly polarized resulting in zero power transfer efficiency.