antenna-theory.com

[pramodh.madhuranath]

Can we make a linearly polarized dipole to be circular polarized? if yes How do we?

What are the advantages and disadvantages if the TX antenna is linearly polarized and RX antenna is circularly polarized?

[admin]

If you have a vertically polarized dipole, you can't make that circularly polarized. CP is vertical and horizontal fields, 90 degrees out of phase (so it looks like the E-field is rotating in time). You have to have some way of getting a horizontally polarized field to exist, and you can't do that with a vertically polarized dipole. You could take two dipoles, feed them out of phase and oriented 90 degrees from each other.....

If tx is linear and rx is cp, then you have 3 dB of polarization mismatch loss. CP is often good for receivers, particularly if you don't know the orientation of the transmit antenna (as in a mobile device a user may hold in any number of ways).

http://www.antenna-theory.com/basics/polarization.php#polarization