Port (circuit theory)
![Network N has a port connecting it to an external circuit. The port meets the port condition because the current I entering one terminal of the port is equal to the current exiting the other.](/Images/godic/202502/03/Port_condition.svg4439.png")
![Simple resistive network with three possible port arrangements: (a) Pole pairs (1, 2) and (3, 4) are ports; (b) pole pairs (1, 4) and (2, 3) are ports; (c) no pair of poles are ports](/Images/godic/202502/03/4-pole_port_arrangements.svg4439.png")
![Coaxial circulators. Circulators have at least three ports](/Images/godic/202502/03/Coaxial_Circulators4439.jpg")
![A Moreno coupler, a type of waveguide directional coupler. Directional couplers have four ports. This one has one port permanently terminated internally with a matched load, so only three ports are visible. The ports are the openings in the centres of the waveguide flanges](/Images/godic/202502/03/Richt24439.jpg")
In electrical circuit theory, a port is a pair of terminals connecting an electrical network or circuit to an external circuit, a point of entry or exit for electrical energy. A port consists of two nodes (terminals) connected to an outside circuit, that meets the port condition; the currents flowing into the two nodes must be equal and opposite.