Asymmetric transversal patch loaded microstrip line based 1-D periodic structure with flexible selection of stopband resonance

A reactively loaded microstrip line based 1-D periodic structure is discussed. An off-centered via configuration is introduced to the conventional center-shorted square patch mushroom type electromagnetic bandgap (EBG) structures. In this work, a rectangular transversal patch is used to load a longitudinal microstrip line reactively. Reactive loading is varied by changing the via position away from the patch center while keeping all other structure parameters constant. This asymmetric loading causes the structure to exhibit EBG characteristics at much lower frequency with the same structure dimensions when compared to conventional centered via setup. Propagating modes are investigated using eigenmode dispersion analysis for different via positions. An equivalent circuit model of the proposed unit cell is developed. Transmission matrix (ABCD) based phase constant calculations for the circuit model agrees with the dispersion analysis results. Finally, experimental results confirm that the proposed asymmetric configuration allows the structure to lower the bandgap resonance by 28.6% with negligible impact on other performance attributes of the structure. Using the proposed configuration, compact filter structures can be designed where the stopband resonance can be flexibly placed in the band of interest within a wide frequency range, by optimizing the via position.