AbstractIn the design of a bandpass filter, the mutual inductance M and the mutual capacitance Cm between two resonators are needed. In this paper, the speed of energy exchange between the coupled LC resonators is related to M and Cm and is defined as the coupling coefficient. Subsequently, the effective M and Cm are determined by deriving the coupling coefficient between the electromagnetic resonators. In this way, a basis is provided on which the filter design theory established previously for the LC resonator circuits is extended to the electromagnetic circuits. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(6): 1–7, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20241