Radiation pattern for a dual band microstrip patch antenna

[mnhtapu]

I designed a dual band microstrip patch antenna resonating freq 3.5 and 5.5 Ghz. I attached the two radiation patterns simulated in CST. The radiation pattern at 5.5 Ghz is different from that of 3.5 GHz. But if you look at S11 graph, return loss is almost same for both frequencies.
I'm afraid that due to the radiation pattern at 5.5 Ghz, the antenna can't be called dual band. Is it mandatory that the radiation pattern at those 2 frequencies should be of same shape?

Any comment is highly appreciable. thanks.

 

[zz0468]

...if you look at S11 graph, return loss is almost same for both frequencies...

I'm not an antenna engineer, but I can make some comments:

Is the return loss really 10db or less for both antennas? Even though there are two distinct resonances visible there, a 10db return loss is marginal at best, and downright crappy for most applications. So, there's work to be done in that regard.

I'm afraid that due to the radiation pattern at 5.5 Ghz, the antenna can't be called dual band. Is it mandatory that the radiation pattern at those 2 frequencies should be of same shape?

It's probably unreasonable to expect the radiation patterns to be identical, but they probably should at least exhibit maximum gain in the same direction, unless there is a specific requirement not to. It's apparent that at 5.5 GHz, there is a null that is not present at 3.5 GHz. That would probably not be acceptable.

What would be more acceptable is, for example, less gain at 3.4 than at 5.5, but patterns that exhibit maximum gain in the same specified direction. In terms of being multibanded, it is typical that the actual gain figures will vary from band to band, but the radiation pattern is predictable, and consistent. Variations in return loss would be acceptable too, so long as both bands are within whatever the specified limits are. A 10db return loss is pretty miserable.

Any comment is highly appreciable. thanks.

Presumably this is a school project. Are there specific design objectives that you are trying to meet?