Miniaturized Reciprocal DMS-DGS Unit and Its Application to Single-/Dual-Band Bandstop Filters

In this brief, a novel miniaturized notch unit achieving a 2nd-order bandstop response is proposed. It consists of a pair of U-shaped defected microstrip structure (DMS) and defected ground structure (DGS) in a reciprocal manner. By integrating these two kinds of bandstop components in the vertical dimension, the filter size could be reduced significantly compared with the conventional bandstop filter. Field analysis, equivalent lumped-element circuit and theoretical derivation are presented. Controllable in-band attenuation could be realized by offsetting the horizontal position of the U-shaped slots, which alters the vertical capacitive coupling due to the change of overlapped area. The proposed reciprocal unit is very promising to implement dual-band bandstop response by expanding the operating principle. Here a 2nd-order dual-band example is illustrated and verified. Both the single- and dual-band 2nd-order notch filters are experimentally verified. The measured results agree well with the circuit-based and EM simulated data.