what is the upper frequency limit of the patch antenna?
Patch antenna can be designed at any frequency theoretically. Usually the dimension of the patch antenna are dependent on the choice of the lower frequency. If u do not use any bandwidth enhancement technique then the impedance bandwidth is usually 6~10 percent of the center/resonant frequency.
Most important factor that directly influence the resonance of a patch antenna excluding the shape of the patch
1) Relative permitivity of the substrate
2) thickness of the substrate
3) substrate size (influence the front to back ratio)
although they have their pros and cons and are selected in accordance with the requirement
Thanks, snkhan.
Usually what kind of bandwidth increasement technique will be used as you mention before?
I know that either decrease the materials permittivity or increase the substrate thickness can increase the bandwidth, with the expense by reduce polariation purity, reduce front-to-back ratio and excite surface wave and lower antenna efficiency.
So what's the pros and cons of the bandwidth increasement techniques? Thanks.
I have seen people using patch antenna up to 100GHz.
As said by snkhan The W/h ratio & εr decides frequency.
see this tutorial for your reference
Abhishekabs
There are many methods of broadening methods. ITs worth wile to look for Borad band antenna techniques by KIN LU WONG. ITs actually not a book but collection his all papers on broadband antenna. Usually slots are used with Patch or ground to enhance the bandwidth as it does not effects much F to B ratio. etc.
Regards
However, if insterting slots on the ground plane, the front-to-back ratio would be deterioated...
You r right but one can also improve F2B ration by increasing the substrate size which inturn increases the ground size.