How does a GPS antenna have only two connections yet have all this circuitry inside?
All that circuitry operates from DC power sent along the signal cable from a DC power supply. The received GPS signal is amplified by the circuitry and sent along the signal cable as a radio frequency (RF) signal to the connected GPS equipment.
The DC power and RF signals are combined and separated by circuits known as bias tees. An inductor (coil) in the bias tee allows DC power to pass through whilst blocking RF signals. A capacitor blocks DC whilst allowing RF through. A bias tee built in to the GPS aerial feeds DC power from the signal cable to the supply rails of the circuitry and connects the received RF signal to the cable. At the equipment end another bias tee allows DC power to be fed to the cable and connects the RF signal to the GPS receiver. This bias tee can either be built into the equipment or provided as a separate (small) box.