Adolfo Velez

Open Complementary Split Ring Resonators (OCSRRs) and Their Application to Wideband CPW Band Pass Filters

In this letter, open complementary split ring resonators (OCSRRs) are introduced for the first time. Such resonators are the dual counterparts of the open split ring resonators (OSRRs), introduced in 2004 by some of the authors, and consist on a pair of concentric hooks etched on a metal layer in opposite orientation. It is shown in the letter that OCSRRs can be modeled by means of an LC parallel resonant tank and that this particle roughly exhibits half the resonance frequency of the complementary split ring resonator (CSRR), hence being electrically very small. The interest of these resonators is illustrated through their application to a wideband coplanar waveguide band pass filter.

Applications of Open Split Ring Resonators and Open Complementary Split Ring Resonators to the Synthesis of Artificial Transmission Lines and Microwave Passive Components

This paper is focused on the application of open split ring resonators (OSRRs) and their dual counterparts, open complementary split ring resonators (OCSRRs), to the synthesis of composite right/left-handed transmission lines, that is, artificial lines exhibiting backward wave propagation at low frequencies and forward wave propagation at high frequencies. Due to the small dimensions of these resonators, the resulting lines are very compact. Several artificial lines, with different electrical characteristics and topologies, are reported as illustrative examples. It is shown that these artificial lines can be applied to the synthesis of dual-band components and bandpass filters, and two prototype device examples are designed and fabricated in coplanar waveguide technology: a dual-band impedance inverter applied to a dual-band power divider, and an order-3 wide-band bandpass filter. Finally, it is also demonstrated that OSRRs and OCSRRs can be combined for the synthesis of band pass filters in microstrip technology. Since OSRRs and OCSRRs are described by means of series and shunt resonant tanks, respectively, and they are electrically small, their potential to the design of semi lumped planar microwave devices is very high.

Varactor-Loaded Complementary Split Ring Resonators (VLCSRR) and Their Application to Tunable Metamaterial Transmission Lines

In this letter, the varactor-loaded complementary split ring resonator (VLCSRR) is presented for the first time. This particle is the dual counterpart of the varactor-loaded split ring resonator (VLSRR), which was introduced previously by some of the authors. Thanks to the presence of the varactor diodes, the electrical characteristics of the particle can be electronically tuned. Thus, by loading a microstrip line with VLCSRRs, the structure exhibits a tunable rejection band which is attributed to the negative effective permittivity provided by the particle. It is also shown in this letter that by adding a gap to the structure, the rejection band is switched to a tunable pass band with left handed wave propagation. Due to the topology of the complementary split rings resonators, the insertion and polarization of the diode varactors is not straightforward. These aspects are discussed in the letter. A circuit model for the VLCSRR is proposed. From parameter extraction and comparison between simulation of the circuit model and experiment good agreement is obtained.

Recent Advances in Metamaterial Transmission Lines Based on Split Rings

This paper is focused on metamaterial transmission lines based on split rings. Specifically, the considered lines are those based on the hybrid approach, where complementary split ring resonators (CSRRs) are combined with series gaps and shunt inductive stubs, and those implemented by loading a host line with open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs). The dispersion characteristics and the characteristic impedance of such lines, essential for design purposes, are analyzed to the light of the lumped element equivalent circuit models of the lines. Finally, it is shown that hybrid lines are useful for the design of power splitters with filtering capability, and OSRR/OCSRR-loaded lines are of interest for the design of wideband bandpass filters. The achieved performances are satisfactory and device dimensions small.

Elliptic-Function CPW Low-Pass Filters Implemented by Means of Open Complementary Split Ring Resonators (OCSRRs)

In this letter, an elliptic low-pass filter (LPF) implemented in coplanar waveguide (CPW) technology by etching open complementary split ring resonators (OCSRRs) in the central strip is presented for the first time. The OCSRRs behave as series connected parallel resonant tanks, whereas metallic patches etched in the back side of the substrate provide the required shunt capacitance to achieve the elliptic function response. An order-5 elliptic LPF has been designed and fabricated to illustrate the possibilities of this new approach. The measured frequency response is in good agreement with the ideal elliptic function up to twice the cutoff frequency (fc=1& GHz). Since OCSRRs are electrically small resonators, filter dimensions are also small (device length is 2.5 cm, namely 0.13 lambda , where lambda is the guided wavelength at fc). This work is illustrative of the possibilities of OCSRRs for the design of compact planar filters and other microwave components.

Reconfigurable bandpass filter based on split ring resonators and vanadium dioxide (VO 2 ) microwave switches

In this paper, we present the design, fabrication and characterization of the first tunable bandpass filter that combines split ring resonators (SRRs) and vanadium dioxide (VO2)-based microwave switches. The device consists on a pair of coupled SRRs, feed by means of tapped microstrip lines, that can be connected to metallic patches by electronically activating the VO2-based switches. Through the fast and reversible Semiconductor-to- Metal Transition (SMT) of the VO2 thin films, the electrical characteristics of the SRRs are modified so that their resonance frequency, and as a result the central frequency of the bandpass filter can be electrically tuned. The fabricated filter, designed to operate in the X-band, exhibits a tuning range of nearly 10% where its electrical characteristics (bandwidth, insertion losses, etc.) are roughly preserved.

Reconfigurable 4 pole bandstop filter based on RF-MEMS-loaded split ring resonators

A reconfigurable four-pole bandstop filter based on the combination of the split ring resonators (SRRs) and RFMEMS switches, operative at the X frequency band, is presented for the first time. The fabricated device consists on a microstrip line loaded with four pairs of SRRs, exhibiting four different resonance frequencies, and two capacitive ON/OFF switches placed between the inner and outer rings of each SRR. Through their electrostatic actuation, the resonance frequency of each SRR can be shifted and as a result filter bandwidth can be digitally controlled, or even suppressed. Good agreement between theory and experiment is achieved.

Low-pass and high-pass microwave filters with transmission zero based on metamaterial concepts

In this work, highly selective filters based on periodic arrays of electrically small resonators are pointed out. The high-pass filters are implemented in microstrip technology by etching complementary split ring resonators (CSRRs), or complementary spiral resonators (CSRs), in the ground plane, and series capacitive gaps, or interdigital capacitors, in the signal strip. The structure exhibits a composite right/left handed (CRLH) behavior and, by properly tuning the geometry of the elements, a high pass response with a sharp transition band is obtained. The low-pass filters, also implemented in microstrip technology, are designed by cascading open complementary split ring resonators (OCSRRs) in the signal strip. These low pass filters do also exhibit a narrow transition band. The high selectivity of these microwave filters is due to the presence of a transmission zero. Since the resonant elements are small, filter dimensions are compact. Several prototype device examples are reported in this paper.

New composite right/left handed transmission lines based on electrically small open resonators

In this work, composite right/left handed (CRLH) transmission lines implemented by combining open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs) are presented for the first time. Both the OSRR and the OCSRR are open particles which can be considered dual counterparts. The OSRR behaves as an open series resonator, whereas the OCSRR can be modeled as an open parallel resonant tank. By connecting the OSRR and the OCSRR in series and shunt configuration, respectively, in a host transmission line, backward and forward wave transmission at low and high frequencies, respectively, is achieved. As compared to split ring resonators (SRRs) and complementary split ring resonators (CSRRs), the open resonators used in this paper are electrically smaller. Thus, compact CRLH transmission lines can be obtained. To illustrate the new approach for the synthesis of metamaterial transmission lines, a CPW-based CRLH transmission line has been fabricated, modeled and characterized. Advantages and drawbacks of the reported approach, as well as potential applications, are also pointed out.

Electrically Small Resonators for Metamaterial and Microwave Circuit Design

A new branch in microwave engineering arose just few years ago with the emergence of metamaterials in 2000 (Smith et al., 2000). The implementation of the first artificial medium with negative effective dielectric permittivity and magnetic permeability opened the door to the experimental study of a new kind of media: left-handed media. The possibility of the artificial implementation of such media allowed the corroboration of many of their electromagnetic properties, predicted years before by Viktor Veselago (Veselago, 1968). Since the year 2000, the interest stirred up by these new materials has given rise to numerous works in a wide range of scientific branches. The possibilities that metamaterials offer to create artificial media with controllable characteristics has permitted the creation of a growing number of completely new applications. Undoubtedly, the most innovative and spectacular application of such artificial media is their use in the implementation of cloaking structures to achieve invisibility, which can be accomplished thanks to the engineering of the refraction index of the different layers of the cloaking shield (Schurig et al., 2006). Within the vast number of new applications of metamaterials, one of the most productive ones is the implementation of microwave devices by means of artificial transmission lines. The following sections will deal with one of the approaches devoted to this purpose: the resonant-type approach. Different subwavelength resonators employed in the design of metamaterial transmission lines based on the resonant-type approach will be studied. The equivalent circuit models of different kinds of metamaterial transmission lines, as well as the parameter extraction methods employed as design and corroboration tools will be also presented. In closing, a selection of application examples of resonant-type metamaterial transmission lines in the design of microwave devices will be presented. 19