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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. == Derivation == As an example, the derivation of the image impedances of a simple 'L' network is given below. The L network consists of a series impedance, ''Z'', and a shunt admittance, ''Y''. The difficulty here is that in order to find Zi 1 it is first necessary to terminate port 2 with Zi 2. However, ''Z''i 2 is also an unknown at this stage. The problem is solved by terminating port 2 with an identical network: port 2 of the second network is connected to port 2 of the first network and port 1 of the second network is terminated with Zi 1. The second network is terminating the first network in ''Z''i 2 as required. Mathematically, this is equivalent to eliminating one variable from a set of simultaneous equations. The network can now be solved for Zi 1. Writing out the expression for input impedance gives; : and solving for Zi 1, : ''Z''i 2 is found by a similar process, but it is simpler to work in terms of the reciprocal, that is image admittance ''Y''i 2, : Also, it can be seen from these expressions that the two image impedances are related to each other by; : 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Image impedance」の詳細全文を読む スポンサード リンク
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