Image impedance

Image impedance is a concept used in electronic network design and analysis and most especially in filter design. The term image impedance applies to the impedance seen looking into a port of a network. Usually a two-port network is implied but the concept can extended to networks with more than two ports. The definition of image impedance for a two-port network is the impedance, Z_i 1, seen looking into port 1 when port 2 is terminated with the image impedance, Z_i 2, for port 2. In general, the image impedances of ports 1 and 2 will not be equal unless the network is symmetrical (or anti-symmetrical) with respect to the ports.