antenna dual polarization

Recently I read a dual polarized antenna and have some questions to ask, the structure of the antenna is as follows:
As the author said, the patch antenna is orthogonally fed by two CPWs, the antenna can work at 2.45GHz with the two polarizations simultaneously, with high port isolation. And the proposed antenna has smaller size than two single polarized antenna working at the same frequency.
But I think when the two ports are simultaneously excitied at 2.45GHz, the current flowing on the patch will be a totally new distribution rather than a simple superposition, and forms a new polarization (not an addition of the two orthogonal polarizations). And this one patch antenna can not be compared with two single antennas at one frequency, they are totally different in nature.

I do not know if I am right. What is your opinion?

Thank you!

This is basic antenna theory. In the patch antenna you excite two orthogonal modes, that is, the fields from the two ports don't interact. Alternatively, as the current flow in orthogonal directions they don't interact.

However, you could feed dual polarized antenna to generate circularly polarized propagation.

Suppose that the amplitude of the two ports are the same, do you mean that if there is a 90 degreee phase difference, a circular polarized antenna can be achived, but when the two ports are of the same phase, they will follow there original way just as one port is fed alone, rather than forming a 45 degree linear polarized antenna.

hi Jone,

i also went through this paper briefly and has the same confusion as ruby does.
as u said, it is well known that a two-port fed rectangular patch with 90-degree phase difference exhibite circular polarization in its farfield radiation. however, what this paper shows is another story, according to the author. the single antenna they proposed is radiating with two orthogonal linear polarizations - at the same frequency! unfortunately the author didn't give us figure about how the surface current on the patch is.

BTW, maybe it's better for ruby to post a copy of this thread on another board-"RF, Microwave, Antennas and Optics", where discussion about concepts and mechanisms is encouraged. it seems it's more appropriate, on this board, for Q&A on commercial software usage.

I haven't read the paper, could you give the reference please.

Either one uses a square patch element to radiate circularly-polarized waves or then it is used for polarization diversity. I think the approach is here polarization diversity. This is an attractive solution for compact antennas: instead of using a two-array antenna one can use a dual polarized element to achieve the same transmission capacity (assuming rich scattering).

It seems like you add the two orthogonal currents Jx+Jy and interpret its far-field as a the new polarization (45°)?

In Dual Polarized antenna patch element is placed diagonally as shown in attached figure.So that from the line of axis each port is 45° apart and the angle between two ports is 90°.

Also Refer https://www.edaboard.com/viewtopic.php?t=335408

regards,
balaguru.

i was totally confused~~~
if the antenna work at 2.45GHz with the two polarizations simultaneously, how about the gain of the antenna?will it be 3dB more than the single polarized antenna?
some can give me an answer?

In order to get 45° you have to sum the two port of this patch with power divider.
so you divide the power to two(=-3db) and sum it back in the patch.
that's why you don't get +3db.

for the circular polarization you need the power divider too and 90° phase shift between ports.

it's not like using two different source of power for each port.

pl