Wideband Passband Transmission Line Based on Metamaterial-Inspired CPW Balanced Cells

In this letter, a balanced metamaterial-inspired coplanar waveguide transmission line with enhanced bandwidth is presented. The coplanar waveguide line is composed of a basic cell with two split-ring resonators, two series capacitances (interdigital capacitors), two wide shunt inductances (metallic strips), and four shunt capacitances (implemented through open-ended stubs). The use of split-ring resonators together with metallic shunt strips provides negative permeability and permittivity, respectively. Likewise, the employment of additional series and shunt capacitances permits to control both the left- and right-handed bands, thus achieving a balanced composite transmission line. The configuration exhibits a wide bandpass response as a result of this balance between advance and delay phase offsets. The interpretation is based on an equivalent circuit model, full-wave electromagnetic analysis, and measured responses of a prototype designed for microwave (C-band) frequency operation. Due to the small dimensions of the resonators employed, the resulting line is very compact. Potential use of these transmission lines can be foreseen in many applications concerning planar microwave devices with severe size restrictions and wide frequency bandpass responses.