help,please!how to increasing the bandwidth of patch antenna

Now I'm designing an array antenna with the feed network. The feed network has wideband with B = 1.3 GHz; but after adding the patch in the feed network the bandwith decrese, just only 90Mhz. Could you help me why? and way to increasing the bandwidth of my antenna. thanks you very much.

I am not an Antenna guy, but your case sounds like a matching issue.

If you could not tune the impedance from antenna and feed network themselves, try to add a tranformer between this two parts.

Hope it helps and welcome any differenct opnion.

A patch antenna (half wave resonating structure close to ground plane) is a narrow band antenna by nature (BW/Fc can be less then 2%). Best is to simulate your patch separately to know the behavior of the patch.

Increasing the height above the ground plane increases the useful bandwidth. You can use a second resonating structure to significantly increase the bandwidth, but with increased design complexity.

a patch with a u-shap slot.

feed at the middle of the U-slot.

Try to get the book: "Compact and Broadband Microstrip Antennas" by KIN-LU WONG. The chapter 7 discusses broad band patch antennas (including the U slot).

Some wide band designs have strong frequency dependent radiation pattern, this may render some designs not suitable for you.

how can you measure that bandwidth is 1.3 GHz and it s decrease to 90 MHz.
i am also designing patch antenna, and use U-slot to increase bandwidth. but do not know how to find bandwidth.
can you please help me //

Bandwidth can be of any figure of merit,like impedance bandwidth,polarization bandwidth, so on. but normally speaking bandwidth which is mostly important in the context is the impedance bandwidth.when you plot your reflection parameters (s11),the frequency area between -10dB points on both sides of resonance is the bandwidth. or in other terms VSWR of less than 2 is the bandwidth of the antenna generally.

Regards
Sajid Mohammed.