Miniaturization, Selectivity and Rejection Bandwidth Improvements of a Multi-Band Stopband Filter Based on Circular Split Ring Resonator

This paper presents a stopband filter design with null gapping between coupled microstrip lines embedded by short-circuited ring resonators. The open and split ring resonators are integrated along the 50-Ω transmission line. Important achievements in size and creation of multiple resonances covering S-band, C-band, X-band, and Ku-band are obtained. Firstly, we load the filter by symmetrical single open ring resonators; this design allows important shifting to lower frequencies accompanied with the appearance of dual band and wide rejection bandwidth of approximately 57.34%. It's noticed that, the proposed filter presents many advantages in comparison with a similar one loaded by stubs. Secondly the filter is loaded by two symmetrical coupled SRR resonators. It is demonstrated that more shifting toward low frequencies and multi-band stopbands are obtained with improvements in selectivity and rejection bandwidth. L-C equivalent circuit models and current distribution for each case were presented and investigated.