circuit board antenna

Hello everybody,

Does anybody already designed a PCB antenna that has a radiation pattern that is symmetrical in the XY plane.

In other words, when the antenna lays on the floor it'll radiate with the same gain in the polar coordinates r-θ-φ whatever the value of φ.

The λ/4 monopole perpendicular to an infinite ground plane has such a radiation pattern. I'd like to avoid having a (big) z-dimension.

Any hint?

Anyone?
Maybe description is not clear enough
Just let me know

As a confusing point, φ is designating the elevation angle in spherical coordinates. Polar coordinates are two-dimensional and have angle Θ only. Thus you may want to clarify your specification.

Regarding the term symmetrical, there are different kinds of symmetry. I understand, that you want to achieve a circular symmetry in the horizontal plane. I think, with low vertical extension, circular polarization is the only way. Two orthogonal λ/2 dipoles, fed by a +/-45° phase shift network can do.

Yes, FvM, you're right about the elevation angle mistake i've made.

Could you detail a little more the antenna design you're proposing? Maybe you have some reference book or scientific article?

Thanks for your help

Circular polarized antennas are often used for UHF RFID systems. They are discussed in some antenna design text books, as far as I remember. Achieving circular polarization by phase shifted feed is a basic RF concept, I guess you'll find many references in the internet. Unfortunately I have no particular link at hand.

Ok, I found many info already. Thanks!

Got another topic to discuss. The chip I use outputs 2 differential signals (180° phase shift). Do you have any idea of how to use that specification in an optimal way to feed an antenna having circular polarization?

I believe we could obtain signals in quadrature by phase-shifting 1 output by 90° using a segment of microstrip but maybe something more elegant could be done based on the "natural" differential signals?

Thanks for any inputs on that issue.

Anyone could tell me if the question is meaningless? :D