Don't know is it true or not, but have read that hobbyist level
nonsophisticated 1W jammer shuts down GPS devices in an area of
hundred kilometres.

The ECM warfare is very well developed field, so it's not a problem to
jam a weak signal at all. Of course, the GPS could be done more or
less jam proof, but it costs a lot of money and hence not practical
for wide use.

There's no difference in jamming radar/comm/GPS, all of them are the
"RF devices", use the same basic principles and communication media.

Russian regards,
Yuri