Enhanching directivity of a microstrip patch antenna

[tensorbundle]

Antenna theory is quite new to me and I found in constantine Balanis's book that there's a relationship between maximum directivity and effective area of an antenna-if we increase effective area, directivity will also increase. The picture of antenna author used to derive the equation was a horn antenna. Is the equation valid for patch antenna?
I want to know another thing-- as patch antenna radiates signal from edges not through the surface, then which area I would consider as effective area for patch antenna?- is it the edge area or surface area of metallic plate?
My aim is to enhance directivity of a patch antenna. so, please provide me some ideas to achieve high directivity.
Thanks

 

[marcusl]

The metallic area is approximately the value to use. Since the dimensions must be matched to the wavelength of the radiation, you aren't able to arbitrarily change the area. To change directivity, you need to do something else--an array of properly phased patches, for instance.

 

[tensorbundle]

a lot of thanks for the reply.

you aren't able to arbitrarily change the area. To change directivity

That's a very good point .

you need to do something else--an array of properly phased patches

Actually I'm designing a patch antenna for my project. An array of patches would make my antenna size many times larger. I don't want to sacrifice miniaturization for the sake of directivity. Perhaps you are an expert in RF field. can you tell me any other possible way to increase directivity without making the patch antenna bigger?
Thanks again for your cooperation

 

[marcusl]

Sorry, I don't know. Maybe someone who knows patch antennas can answer this question.