Interference for cell phones

Again in search of physics understanding.

If a microwave beam is coming down vertically onto the rectenna,
without much leakage beyond the rectenna boundaries, could we use
the same frequency as that already allocated to cell phones, with
the understanding that there would be no cell phone transmissions
within the rectenna zone.

My gut tells me it's not going to be as simple as that, but I'm not
sure as to the why of it?

Anybody interested in explaining this issue.