Potential of Interresonator Tapped-In Coupling in the Design of Compact Miniaturized Electromagnetic Interference (EMI) Filters

In this paper, we present for the first time the realization of interresonator coupling through a tapped-in structure. This new coupling structure is used to design miniaturized filters. This coupling is of inductive nature, and it is created through transmission line directly tapped into resonators. This transmission line operates in its fundamental transverse electromagnetic (TEM) or quasi-TEM mode. Large coupling values based on traditional coupling mechanisms are either unachievable or poorly realized by engineering the resonator structures. However, the tapped-in coupling method easily provides weak to strong coupling values. Therefore, implementation of the interresonator tapped-in method simplifies the design of compact wideband filters, which require strong coupling values by using the minimum number of resonators. Moreover, coupling realization based on this method is less sensitive to manufacturing precision. The potential of this method to increase interresonator coupling which leads to bandwidth widening is comprehensively illustrated through simple examples of two-pole combline filters. The numerical and measurement results verify the performance of tapped-in coupling mechanism.