A Novel Compact Coplanar Waveguide Bandstop Filter Based on Split-Ring Resonators

The miniaturization of microwave filters based on planar technology are important issue for integrated and miniaturized transceiver front-ends. In this view, a novel design method using metamaterials showed the possibility of a compact size filter. In the last decade, these can be realized through electronic band gap (EBG) structure and Left-handed material having negative permeability and negative permittivity have been proposed [1]-[3]. These simultaneously exhibit unusual characteristics which can pass specific frequency bands or suppress parasitics, undesired spurious bands and harmonics. Traditionally, these filtering characteristics are realized by using a half wavelength short-stubs or lumped elements. This method have, however, drawbacks of large size, narrow bandwidth, low performance due to noise. In the last several years, a number of researches on EBG structure had been done for reducing these drawbacks [3]-[4]. The EBG structure is usually designed to have periodicity so that it prevents wave propagation at specific frequency band [2]. The advantages of those structures is that they can be integrated in a device without additional space. This is encouraging method in respect to fabricating a much smaller size device than traditional ones. However, there are some problems in miniaturizing because those structures require several stages for sufficient bandstop characteristics. Recently, several structures which have effectively negative permeability or negative permittivity have showed up for more compact device characteristics than early EBG structures. One of these structures is the split-ring resonator (SRR) proposed by J. B. Pendry [5].