Application of complementary split-ring resonators to the design of compact narrow band-pass structures in microstrip technology

In this paper, a compact and narrowband microstrip band-pass structure based on complementary split-ring resonators (CSRRs) etched in the back metal level (ground plane) is presented. Specifically, the structure is a two-stage CSRR-based device, where a series gap is etched in the output CSRR stage and two shunt stubs are added in the input cell. By these means we obtain a narrow and quite symmetric band-pass structure. A prototype device with 2% fractional bandwidth has been designed and fabricated for operation at the S-band. The dimensions of the device are as small as 14.6 × 11 mm, while high-frequency selectivity is achieved at both band edges due to the presence of two transmission zeros. To demonstrate the possibility to control the bandwidth over a narrow band, a wider (10% bandwidth) filter has been also designed and fabricated. These structures can be of interest for application in narrow band-pass filters where miniaturization and compatibility with planar technologies are key issues.