If line of sight to the jamming antenna is required to be jammed, why do aircraft not have a downwards shield so that they only receive GPS signal from the sky (satellites) and not from jammers (coming from the bottom hemisphere)? Or is the jamming signal so many orders of magnitudes stronger than the satellites that there's always going to be some gain no matter how good the shield is?
Ok it exists, but shielding is (only) about 20dB looking downwards, which may not be enough: https://safran-navigation-timing.com/product/8230aj-gps-gnss...