HELLO Hafez,

it depends on your application, i think Horn antenna, or reflactor antenna are a good choice for CP

b.REGARDS

Well, as the previous responder said, it depends on what you're trying to optimize. One answer is that conventional antennas are reciprocal, so they are just as good at receiving a particular radiation pattern as they are at transmitting it -- so if you're helical antenna is producing circularly-polarized waves (right- or left-handed) then another helical antenna could receive it.

On the other hand, depending on your application, you may be satisfied with a wide beam pattern on the transmit side (e.g. broadcast) but want something more directional, with more gain, for receiving. In that case, a horn with a parabolic reflector may be more optimum assuming size is no constraint. A horn will need some kind of polarizer or quarter-wave plate to capture circular polarization, however.

As said by Mohammad Hafez Seada, wave are generator by circular ( helical ) antenna, but we can use two type of antennas to receive signal waves like; helical antennas and also linear antennas. Linear antennas can receive circular polarized signal too.

Hi Hafez,

U can also use microstrip (patch) antenna with different feed. I mean you can make patch antenna and feed it through some power divider and can get circular polarization. It should be 90 degree phase difference.

Another helical antenna (of the same sense) will receive it perfectly well.  Don't use linear unless the advantages of circular polarization really don't matter to you - one of the advantages is that it rejects reflections from the ground, called multipath, so you don't get nulls at constant intervals above the ground or beside walls.  You also lose 3 dB if you receive circular with a linear antenna.

"...a helix antenna with the opposite circular polarization would be a very good choice."

Are you sure, John? I think you want an antenna with the same circular polarization, not opposite. As a memory/visualization device, I think of two standard screws, both threading into the same tapped hole from opposite ends. So two IDENTICAL helixes pointed at each other should transmit and receive the same circular polarization.

You are right Matthew - I was careful to get it right in my advice in the previous post.

There are many possibilities, some better suited to certain frequency bands and applications than others. You ask for an "optimal" antenna, do you mean one which is optimised to give the purest circular polarisation, or do you have a different optimisation goal in mind?

Anyway, possibilities include, microstrip patches, circular waveguide horns, loop and helical antennas and spiral antennas or any of these feeding a parabolic reflector, including Cassegrain designs. Then again, there are various polarisation filters that will convert a plane polarised signal to circular polarisation, and visa-versa.  Consult Antenna Theory Analysis and Design by C. Balanis.