In this paper, a design of very compact microstrip bandstop filters based on complementary split ring resonators (CSRRs) is proposed. Two techniques of metamaterial miniaturization are used to optimize the physical and electrical size of the CSRR. The bandstop filter is produced by an array of miniaturized loaded CSRRs etched on the center line of a microstrip. The size of the proposed filter, is as small as 0.58 cm2, and its electrical length is very small with only 0.08 λ0), compared to a conventional bandstop filter, a miniaturization of a factor 5 while the bandstop performance is maintained. A very good agreement obtained between the measurement and the simulation results.
Many modern telecommunications systems, such as the embedded systems, systems of mobile phone and wireless communication, use filters; many conventional filter designs has reached their technologically defined limits. To satisfy the increasing demand for high performance, circuit integration and reduced size, alternative concepts have to be explored [
In recent years, left-handed Metamaterials have attracted considerable interest of scientists and engineers working in the field of microwave technology. These Metamaterials exhibit both a negative permittivity and permeability which result in a negative index of refraction, a property not available within any natural material [2-4]. From duality arguments, it has been shown that negative permittivity media can also be generated by means of a resonant element, namely the complementary split ring resonator (CSRR) introduced by Falcone et al. in 2004 [
In previous research of some of the authors, SRRs and CSRRs have been successfully applied to the design of microwave filters [6,7].
The aim of this paper is to apply a bandstop filter synthesis proposed in the literature [
In Section 2, we propose a design of conventional bandstop filter based on CSRRs etched on the center line of a microstrip. In Section 3, I will describe how to obtain a reduction of the filter size by the optimization of electrical and physical CSRR size. Finally, in Section 4, the obtained calculated results are discussed and compared with measurements.
A conventional bandstop filter based on a 50 Ω line and the CSRR etched in the conductor strip [
CSRR is dual counterparts of SRR. Therefore a dual electromagnetic behaviour for them is expected according to the duality theorem. The incident electric field needs to be polarized in the axial direction of the resonator. In this way, CSRRs are etched on center line of the microstrip technology.
This arrangement makes sure that the CSRRs are properly exited by the electric field applied parallel to the ring axis.
The CSRR topology and equivalent circuit model are illustrated in
The substrate used is a RT/Duroid having the following characteristics (relative permittivity εr = 2.2, loss tangent tg(φ) = 0.0001 and thickness h = 0.8 mm).
The resonator is simulated by using a commercially available 3D full-wave solver (Ansoft HFSS).