One-dimensional photonic bandgap structures by periodically loaded rings on microstrip line

We show both experimental and theoretical results on a new kind of one-dimensional photonic bandgap (PBG) microstrip. The PBG structure is introduced by periodically loading rectangular rings on conductor strip of microstrip. Numerical simulations show that the size of the rectangular ring effectively attributes to the optical length of the unit cell and scales the center frequency of PBG. This method also provides an option to realize compact PBG microstrip at lower frequency by adopting rings with longer lateral size. Multiple defect modes can be obtained and tuned by varying the size of the rectangular ring or the length of the interconnected strip between the two adjacent rings at the center of the PBG microstrip structures. Experiments are in good agreement with simulations. Insertion loss of the defect modes can be controlled in a low level without any optimizations.