>That’s why I was asking, the jammer would have to be very strong to overwhelm a "real“ signal which is located in the main lobe when the jammer is outside.
The mobile jammer in the article's scenario is transmitting toward the satellite, not the terrestrial terminals on the ground.
Imagine in the primitive example case that the "real" signal transmission must also be coming from a terrestrial terminal as well. The real terrestrial terminal is likely be similar in size to the mobile jammer, and subject to the same kinds of constraints as the jammer. However, the jammer doesn't have to consider much about the quality of its radiated energy at the target frequencies. Let's also assume that that both the real transmission terminal and the jammer can emit the same amount of energy.
The distance between both the real transmission terminal(s) and the jammer to the communications satellite, for all practical purposes, is roughly the same.
From the primitive example communications satellite's perspective, it will see/hear both the real signal and an equally "loud" signal (noise) at the same frequencies. When the communications satellite relays or retransmits what it hears to the receiving terrestrial terminals, it will be the combination of what the satellite saw/heard.
Instead of the "bent pipe" imagine another primitive example where the communications satellite is an optical mirror, and the "real" signal comes from a light source on the ground pointed at the satellite. The "real" signal could be represented using different modulations of that light in brightness, frequency/wavelength, as well as temporal pulses. Terrestrial receivers decode the "real" signal based on the flashes of light it observes from the mirror. The jammer in this scenario is another light source pointed at the same mirror.
Terrestrial, ground-based jammers are not the only type of potential jammer in a satellite communications system's operational scenarios. In the prior example ground-based jammers look upward to jam the satellite. You can also imagine scenarios where airborne jammers are possible, which look downward to jam receiving terrestrial terminals.
A ground-based jammer versus an airborne jammer would have a few differences. The ground-based jammer mostly needs to consider a fairly well-known location of the communications satellite, as the satellite can be easily observed, and its future positions can be calculated using ephemeris data, for targeting. An airborne jammer would have to deal with the issue that it has a lower field of view than the satellite beam's footprint and needs to have more specification information about the location of terrestrial receiving terminals to apply its own area of effect, which would be smaller than the satellite's beam. However, the effective distance between the airborne jammer and terrestrial terminals will be orders of magnitude lower than the communications satellite and terrestrial terminals. Power transmission capacity is a constraint for all terminals, satellites, etc, and an airborne jammer's ability to apply power will be more effective than satellites due to distance, but the airborne jammer must be more selective on where to apply (i.e. target) that power.
One jammer could be used to affect the transmission signal, but it would likely take many jammers to target receiving terminals when there are many geographically dispersed terminals.