One comment on “The concept of coupling

  1. It is worthwhile mentioning that the concept of coupling usually implies the assumption that the couplings involved are frequency independent. This is an ideal condition that strictly does not exist in the real world. Every physical coupling structure is frequency dependent. A quasi frequency independency may only be assumed over a very narrow frequency range around a bandpass filter’s center frequency. It is therefore not possible to correctly analyse a filter over a wide frequency range on the basis of a coupling matrix with ideal frequency independent couplings.

    In the design of bandpass filters with wide passbands, the coupling matrix approach is of very limited value as it does not take into account the frequency dependency of the physical coupling elements. Perhaps for the initial design of a wide bandpass filter the coupling matrix is of some value but actual filter responses need to be checked by using electromagnetic simulation. On the basis of the latter, information on the nature of the frequency independent couplings can be obtained.

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