Waveguide port dimensions in simple microstrip antenna desig

Hello,

I'm designing simple microstrip antenna. I'm using waveguide port. Is there any way to estimate the dimensions for the waveguide port?
I'm asking becasue I tried many dimensions and for every one there is different input impedance and different bandwidth of the last result at -10dB!!!!!!

Regards

I'm not sure what software you're using, but a good rule would be that the width should be +/- 4 times the feed width and the height should be 4 times the substrate depth.

The 2D Eigen mode solution of the port will show you if it is too small I woudl expect.

Hello,

I'm using CST. These 3, 4 times are something from your experience or it is written somewhere ?

Regards

This is the figure given from their training slides and Ive used it in practice and it covers most situations.

You can always check by looking at the port mode (2D result), if you see some cones showing the E-field outside the port area then it's best to enlarge the port dimensions.