There is a brand new, small, and simplistic satellite antenna developed by the European Space Agency.
It was specifically created to track global ship traffic from orbit, designed to fit inside mini-satellites.
Incredibly, up to five of these 20 inches wide by 1 inch deep satellites could be installed on a single cubic-meter mini-satellite.
The ESA further explains:
Commercial vessels are mandated to transmit Automatic Identification System (AIS) signals, which are used to track maritime traffic – the oceangoing equivalent of air traffic control. The system relies on VHF radio signals with a horizontal range of just 40 nautical miles (74 km), useful within coastal zones and on a ship-to-ship basis, but leaving open ocean traffic largely uncovered. However, in 2010 ESA fitted an experimental antenna to Europe’s Columbus module of the International Space Station, demonstrating for the first time that AIS signals could also be detected from up in orbit, opening up the prospect of global ship tracking from space.