Wi Max patch antenna
Hello,
If you start from a circular polarized patch (that used a divider with 90 degr phase shifter), you can make your patch. Do not start with a circular polarized patch that uses one feed only.
Make sure your patch width is same for X and Y directions (for example square, circle, etc). Some internet search will provide you examples. Each linear patch with same X and Y direction (eq. square, circle) you can use for dual polarization.
Conversion to dual polarized, +/-45 degr slant linear
Remove the divider and 90 degrees phase shifter. Now you have two inputs to the patch that provide orthogonal polarization. With that patch you can make polarization diversity (lin/vert, 45, -45 slant linear).
When you started from a linear patch, just add the second port 90 degrees rotated. Because of this, S12, S21 will be low.
Reducing the height of the patch above ground, reduces useful bandwidth and increases edge-fed impedance. If required you can make the impedance transformation with quarter wave sections. Of course you can also use two probe feeds.