Frequency Characteristics of 1-D Periodic Structures with Tapered Microstrip Lines

The electromagnetic bandgap (EBG) structure is a kind of photonic crystal that can be used in microwave and millimeter-wave frequency regions. In this paper, we present the analysis and design of two types of periodic structure circuit with one-dimensional (1-D) EBG structures using alternately arranged, linear, tapered microstrip line (MSL) elements. In order to design the circuits, we calculated their frequency characteristics on the basis of transmission line models. First, we found an ABCD matrix using a model consisting of very short, series-connected MSL elements. Thereafter, we converted these ABCD matrices into S matrices. Based on the theoretical analyses, we fabricated two types of circuits on printed circuit boards (PCBs) and evaluated their frequency characteristics. The results of evaluation showed that one of the circuits had a stopband of 2 GHz bandwidth and the other had a passband in the center of the stopband. The measured and calculated results were found to be in good agreement. (C) 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.