Relation between S11 and S21, S21 and antenna gain!

Hello Everyone,

I want to ask if there is any relation between S11 and S21 for the antenna. Usually we take the antenna as one port device. But If we take the feed port of antenna as one port, and the radiation port of antenna as another port, the antenna becomes two-port device. In this way, I saw one equation, |S11|2+|S21|2=1.

Can anybody tell me more details about the relation between S11 and S21 for the antenna.

Another question is: what is the relation between S21 and antenna gain for the antenna? Are they equal and same or not?

Thank you very much!

Jack

You can refer to this paper:
http://ieeexplore.ieee.org/xpls/abs_...number=4897428

This "power conservation" is valid for a lossless circuit only.

There is no "port 2" in the antenna, so it is difficult to answer. But it would help you anyway: The S-Parameters do not tell us anything about the radiation pattern and antenna gain.

The antenna gain is the result of beamforming: more radiation into one direction (=gain over an isotropic radiation) and less radiation in other directions, where the total radiated power is still the same. This beamforming is not visible in the S-parameters.

Antenna directivity and antenna gain:
http://en.wikipedia.org/wiki/Directivity