Microstrip line periodic structures with capacitive and resonant element loads

In this paper, two microstrip line periodic structures, respectively loaded with capacitance and resonant elements, are investigated. The theoretical analyses describe the difference of the two bandgaps happening to the resonant elements loaded periodic structure. From the k-β diagrams, it is found that the stopband, obeying Bragg´s law, can be enhanced by increasing the capacitance in the loads. Based on the theory, both the capacitively loaded and resonant elements loaded periodic structures are realized in two-layer microstrip lines. The equivalent LC values are extracted with a quasi-static method, and they are used for circuit optimization. Besides this, a method to improve the bandstop performance is proposed and validated theoretically and experimentally.