Question

A transverse electromagnetic wave 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

• A. 0%
• B. 35.3%
• C. 50%
• D. 25%

Answer 1

The correct option is A 0%

Ans : (d)

Polarization loss = ${\left|cos\theta \right|}^2$

where $\theta$ is angle between received and transmission E fields of antennas.

Polarization loss = ${\left|\frac{E_T\cdot E_R}{\left|E_T\right|\left|E_R\right|}\right|}^2$

$E_T=({\hat{a}}_x+j{\hat{a}}_y)$ circular polarization

$E_R=\left({\hat{a}}_{x}or{\hat{a}}_y\right)$ linear polarization

Polarization loss = ${|\frac{({\hat{a}}_x+j{\hat{a}}_y)}{\sqrt{2}}\cdot {\hat{a}}_x|}^2$

= $\frac{1}{2}=50$% = -3 dB

A dipole antenna is usually linearly polarized and given is circularly polarized resulting in zero power transfer .