Gold Meritorious Patron
You can never 'tap' a beam with another beam. Microwaves don't talk to each other. You could intercept a microwave transmission by sticking an antenna into the 'beam', but sending another 'beam' through the first one will extract no information at all. Electromagnetic waves just don't work like that. They pass through each other without affecting each other at all.
On the plus side, for an eavesdropper, electromagnetic transmissions don't normally travel in perfect 'beams'. Sending electromagnetic signals is like throwing stones into a pond. Try doing that in such a way as to send out a thin stream of waves in just one direction. You actually can arrange for a lopsided wave pattern, if you throw the stones right, but you can't herd the waves in a perfect column. Microwaves are waves of electromagnetic field strength instead of water height, and are generated by moving charges instead of dropping stones; but they're still like water waves in many ways. Even if you can arrange for the bulk of your wave power to head straight for your intended receiver, some of it goes in other directions, and an eavesdropper can probably still pick up your signal with a little antenna somewhere else. Like maybe even behind your transmitter.
You could probably do tight line-of-sight communication with laser beams, though even they're going to spread, if you're communicating across miles. A laser beam is still just the best case of a lopsided wave pattern, generated by moving charges just right.
Failing a laser beam, you have to assume that someone who wants it can pick up your signal. If you want secrets, encrypt.
Do they require a permit that might be public record?