> These antennas have a very good idea of where the signal is coming from, due to delay measurements "These antennas" is doing an impossibly large amount of wo

> These antennas have a very good idea of where the signal is coming from, due to delay measurements "These antennas" is doing an impossibly large amount of work. What you are describing here is a delay-calibrated coherent receiver, not an antenna, and it's absolutely not "inexpensive" to pull this off. With passive antennas, most of the attenuation of adversarial signals is being done by the relatively-high-directionality of planar arrays: off-boresight signals have far greater attenuation with these (20dB? - tricky because you still do want good satellite data close to the horizon), and most garden variety jammers are terrestrial and off-axis. Still, these signals are always below the noise floor and mostly unsigned, it's somewhat easy for an airborne (or spacefaring) jammer to fully drown out, replay/time-shift, or spoof the signal.