A phantom loop is an electrical network that uses part of the natural environment to complete a circuit. It is a form of an open system .

Examples include:

• The space tether, also called "electrodynamic tether", which uses plasma contactors and the ionosphere, plus the electromagnetic induction from Earth's magnetic field, as parts of a dynamo (or an electric motor), to turn the kinetic energy of the spacecraft into electrical energy (or conversely).
• The Tesla coil, which can form a natural circuit.
• The long-distance electromagnetic telegraph, which in some cases used the ground as the return path for the circuit.
• Single wire earth return power distribution systems for supplying power at low cost to remote areas.
• Some high-voltage direct current power transmission systems.

Phantom loops can occur in suspended circuits, in which the conductor has no ground and uses the ionosphere to complete the circuit at both ends. Phantom loops can also occur in grounded circuit, in which the conductor has a ground and uses the lower atmosphere to complete the circuit and both ends (with the waves traversing the magnetic poles of the Earth).