There can be a problem in size or position or dimensions.... Please check correctly by zooming to extreme case.....

CST will Boolean add objects that don't touch and are different materials, so those things don't matter.

Try overlapping them deliberately - make the feedline overlap the patch.

@Anveshkumar and @Malcolm

Thank you so much for your valuable contributions, I have tried the overlapping approach as suggested by @Malcolm and it worked pretty nicely.

Thanks once more.

If you design the recessed distance from the slot with a material other than the vacuum, CST considers the existence of this material in the event of the manipulation of the boolean function. Try to make it with the vaccum

What I found to be the cause of the boolean add operation's failure to combine the two shapes, say A & B, was due to the fact that the working coordinate systems (WCS) in the Z axis of the two shapes were pointed in the same direction for the copper thickness (t) with the same positive (+) arithmetic sign, that is, t, t instead of with (+ & -) t, -t in the Z axis for the two shapes A & B, respectively.

Once you get this sorted out, the boolean add operation will combine together the two shapes effortlessly.

Dear Henry Ojukwu ,

I know that you have now more one solution which means that these are not only methods that can be used to combine the two shapes.

I think you can use geometrical operations to combine the two shapes as you with. I mean you can used rotate and shift to combine them as you wish.

Best wishes