> Jammers (to my knowledge) operate by actively producing an inverted copy of the signals it actually sees.
No. Usually, all you need is to do is to send a signal - any signal - on a frequency you want to jam with enough power to overwhelm the target signal. A directional antenna won't get a milliwatt satellite signal if it starts picking up half a kilowatt of random noise, even if that noise is coming from the side. It's essentially a matter of how much power your jammer radiates and how high you can put it. Whether or not jamming interferes with other radio communication depends on how much of the spectrum your jamming signal covers.
Seems like it'd be pretty straightforward to block signals coming from the side (e.g. by putting some metal or something else similarly RF-blocking between the antenna and the jammer), no? Kinda like how wearing a hat helps keep the sun out of your eyes. Actively jamming the jammer (i.e. inverting the signal received from the jammer side and rebroadcasting on the the antenna side) would help, too, though this probably makes it easier to detect. And yeah, the higher the jammer, the harder it is to block it without blocking the signal you're trying to actually see (but it's still possible; if it wasn't, then modern astronomers would have a much harder time picking out interesting things amidst the menagerie of cosmic background radiation bouncing about).
There are plenty of other strategies, too (like not sticking to a single frequency, or picking frequencies that are likely to be too valuable to block with such a blunt-force method).
> Seems like it'd be pretty straightforward to block signals coming from the side (e.g. by putting some metal or something else similarly RF-blocking between the antenna and the jammer), no?
Depends on the wavelength and your surroundings. Imagine yourself wearing a cap that's little too small and half-transparent on the edges, walking on fresh snow, surrounded by snow mounds, trying to spot something on one of the hilltops nearby. So the cap mostly protects you from direct jamming signal, but reflections and bleed are still painful.
Now we're talking here about satellites, in particular LEO satellites, so you need a mass market (or at least commercial-grade) tracking antenna, which will have to look all across the sky and not just point straight up. In urban environments, there's a great chance there will be scores of decent reflectors (buildings) all around you for the jamming signal to bounce off, and as for bands, the ones used by Starlink are ones that are unlikely to be used much for anything else in places like Iraq - so they may as well just jam the whole band. And since Starlink is a commercial service, you won't be able to switch to something the government depends on (not to mention procure new antennas and adjust software on the transceivers).
> Imagine yourself wearing a cap that's little too small and half-transparent on the edges, walking on fresh snow, surrounded by snow mounds, trying to spot something on one of the hilltops nearby. So the cap mostly protects you from direct jamming signal, but reflections and bleed are still painful.
The usual answer, then, would be a polarized filter and a more narrow aperture (e.g. goggles). The narrower the FOV, the less risk of glare.
That does mean an antenna will have to actively keep itself pointed at a moving point in the sky, but with GPS, a compass, a clock, and each satellite's orbital parameters, that should be a solvable problem.
The harder problem would be for the satellite to pick out the signal coming back from the ground without having to limit itself to a single ground station.
No. Usually, all you need is to do is to send a signal - any signal - on a frequency you want to jam with enough power to overwhelm the target signal. A directional antenna won't get a milliwatt satellite signal if it starts picking up half a kilowatt of random noise, even if that noise is coming from the side. It's essentially a matter of how much power your jammer radiates and how high you can put it. Whether or not jamming interferes with other radio communication depends on how much of the spectrum your jamming signal covers.