Using monopole patch for wider bandwidth, how to cancel radiation on 2nd pcb side?

Hello! I am learning about monopoles using microstrip patches without ground plane. I want to ask what is best option to cancel radiation on the second side of PCB, when we do not need omnidirectional 360deg pattern, but only < 180deg.

I see such options:
1. put an microwave absorber (but we lost 50% of power)
2. using machined cavity with some height to reflect radiation back to monopole or something like that.

Any suggestions?

Placing any metal close to the microstrip patch designed without ground, would act as a ground and will decrease the bandwidth of the antenna. A standard patch antenna with ground have BW about 5%.
An option would be to use a pattern ground (search the net for a shape) placed at relative high distance from the patch, but this will require intensive EM simulation to get the optimum.
Other option that increase the BW of the patch antenna (other than dielectric height and type, or adding parasitic patch elements) is to place a ground at some distance and a U-shape slot into the patch. This also require EM simulation.

Thank for your reply. There are many information on U-slots online. I also found this interesting:
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maybe someone would be interested in microstrip LPMA patches.