> Given that GPS/GNSS comes from satellites, ignoring signals from not-from-the-sky seems like a quick win. You're right, but GPS antennas already have some re

> Given that GPS/GNSS comes from satellites, ignoring signals from not-from-the-sky seems like a quick win. You're right, but GPS antennas already have some rejection from the "bottom" hemisphere. So they're already rejecting not-sky. CRPAs (of the type contemplated by ITAR) are electronically steerable antennas (phased arrays), that allow you to steer one or more nulls to the direction of the noise source(s). That gives much better rejection of point-source noise.