Comment by summa_tech

Imagine a power splitter + phase shifter that produces a correct phase shift for each element in a phased array to produce a directional beam from one radio transceiver.

Now this clever arrangement, instead of having only one radio transceiver port, has multiple. And each of those ports corresponds to a different set of phase shifts, producing a directional beam at a different azimuth angle.

And because this is an entirely passive device, it's linear, and all ports can be active at the same time (principle of superposition essentially). So you can use a single phased antenna array to serve multiple directional beams at the same time.