Ignacio Gil

Equivalent-circuit models for split-ring resonators and complementary split-ring resonators coupled to planar transmission lines

In this paper, a new approach for the development of planar metamaterial structures is developed. For this purpose, split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) coupled to planar transmission lines are investigated. The electromagnetic behavior of these elements, as well as their coupling to the host transmission line, are studied, and analytical equivalent-circuit models are proposed for the isolated and coupled SRRs/CSRRs. From these models, the stopband/passband characteristics of the analyzed SRR/CSRR loaded transmission lines are derived. It is shown that, in the long wavelength limit, these stopbands/passbands can be interpreted as due to the presence of negative/positive values for the effective /spl epsiv/ and /spl mu/ of the line. The proposed analysis is of interest in the design of compact microwave devices based on the metamaterial concept.

Novel microstrip bandpass filters based on complementary split-ring resonators

In this paper, a new methodology for the design of compact planar filters in microstrip technology is proposed. This is based on cascading filter stages consisting of the combination of complementary split-ring resonators (CSRRs), recently proposed by the authors, series capacitive gaps, and grounded stubs. By this means, we achieve the necessary flexibility to simultaneously obtain quite symmetric frequency responses, controllable bandwidths, and compact dimensions. Two prototype device bandpass filters are provided to illustrate the potentiality of the proposed approach. In the first prototype, the structure is periodic (i.e., composed of identical cells) and behaves as a left-handed transmission line with controllable bandwidth. In the second prototype device, periodicity is sacrificed with an eye toward the synthesis of a standard (Chebyshev) approximation. The measured frequency responses point out low insertion losses in the passband, as well as high-frequency selectivity with small dimensions. As compared to conventional parallel coupled line filters, reduction of device length by a factor of 2.4 is demonstrated. This is the first time that planar filters with controllable bandwidth based on CSRRs are achieved. These structures can be of interest in those applications where miniaturization and compatibility with planar circuit technology are key issues

Microwave filters with improved stopband based on sub-wavelength resonators

The main aim of this paper is to demonstrate the potentiality of sub-wavelength resonators, namely, split-ring resonators, complementary split-ring resonators, and related structures to the suppression of undesired spurious bands in microwave filters, a key aspect to improve their rejection bandwidths. The main relevant characteristics of the cited resonators are their dimensions (which can be much smaller than signal wavelength at resonance) and their high-Q factor. This allows us to design stopband structures with significant rejection levels, few stages, and small dimensions, which can be integrated within the filter active region. By this means, no extra area is added to the device, while the passband of interest is virtually unaltered. A wide variety of bandpass filters, implemented in both coplanar-waveguide and microstrip technologies, have been designed and fabricated by the authors. The characterization of these devices points out the efficiency of the proposed approach to improve filter responses with harmonic rejection levels near 40 dB in some cases. It is also important to highlight that the conventional design methodology for the filters holds. For certain configurations, the presence of the resonators slightly lowers the phase velocity at the frequencies of interest with the added advantage of some level of reduction in device dimensions.

On the electrical characteristics of complementary metamaterial resonators

In this letter, a method to obtain the electrical characteristics of complementary split ring resonators (CSRRs) coupled to planar transmission lines is presented. CSRRs have been recently proposed by some of the authors as new constitutive elements for the synthesis of metamaterials with negative effective permittivity, and they have been applied to the fabrication of metamaterial-based circuits in planar technology. The method provides the electrical characteristics of CSRRs (including the intrinsic resonant frequency and the unloaded Q-factor), as well as the coupling capacitance between line and CSRRs, and the parameters of the host line. Parameter extraction from the proposed method is applied to two different structures corresponding to the basic cells of left handed (LH) and negative permittivity lines. The method is of actual interest for the design of microwave circuits and metamaterials based on these complementary resonant particles

Metamaterials in microstrip technology for filter applications

In this work, backward (or left handed (LH)) transmission lines in microstrip technology are designed and fabricated. To this end, the line is periodically loaded with square shaped split ring resonators (SRR), etched in close proximity to the conductor strip, and via holes. The SRR provide the negative effective permeability, /spl mu/, to the medium in a narrow band above their resonant frequency, whereas the metallic vias act as shunt connected inductors that make the structure behave as a microwave plasma with negative permittivity, /spl epsiv/, up to the plasma frequency. It is shown that in that region where both /spl mu/ and /spl epsiv/ are simultaneously negative, left handed wave propagation is allowed. Since this occurs in a narrow band above SRR resonance, and the period of the structure is electrically small, these metamaterial transmission lines can be of interest for filter applications where miniaturization and narrow pass bands are pursued.

Applications of Right/Left Handed and Resonant Left Handed Transmission Lines for Microwave Circuit Design

Additional degrees of freedom in a design of miniature microwave devices can be provided by a combination of right-handed (RH) and left-handed (LH) transmission lines (TL), which differ in dispersion characteristics. We present some examples of such devices: planar resonator and filter with suppressed spurious response as well as a miniaturized matched balun and broadband digital phase shifters. Whereas these structures follow the right/left-handed TL approach, it is also possible to implement left-handed structures by following the resonant type approach, i.e. by using split rings resonators or complementary split rings resonators. Examples to illustrate the possibilities of this approach are also presented

Limitations and Solutions of Resonant-Type Metamaterial Transmission Lines for Filter Applications: the Hybrid Approach

In this work, the main limitations of resonant-type left handed transmission lines for filter applications are pointed out. Naturally, microstrip lines periodic loaded with series capacitive gaps and complementary split rings resonators (CSRRs) exhibit a band pass behavior with backward wave propagation in the allowed band. Cell dimensions and selectivity at the lower band edge are satisfactory. However, the upper transition band, in-band losses and bandwidth should be improved for the competitiveness and applicability of these devices. It is shown in this contribution that by introducing grounded inductive stubs to the basic cell, the previous limitations can be overcome. Actually the resulting structure is a combination of the CSRR-based (i.e. resonant-type) left handed line and the dual transmission line concept. For this reason this approach has been termed as the hybrid approach. Its advantages and potentialities for the design of small size high performance band pass filter are highlighted, and several prototype device examples are provided to illustrate the achievable performance

Super Compact (<1cm2) Band Pass Filters with Wide Bandwidth and High Selectivity at C-band

In this work, it is demonstrated that planar microwave filters operative at C-band can be realized with simultaneously very small dimensions (area A<1cm2), wide bandwidth (fractional bandwidth FWB>45%) and high frequency selectivity (transition bands with more than 50dB/GHz fall-off at both band edges). This is possible thanks to the development of new innovative concepts for planar filter design. Specifically, we have considered two alternative approaches: (i) one based on the use of metamaterial resonators, such as complementary split rings resonators (CSRRs), combined with inductive stubs and series gaps, and (ii) another based on semi-lumped resonators coupled through 90deg meanders lines acting as admittance inverters. In both cases, key to achieve the small dimensions is the sub-wavelength operation of the resonant elements. The simultaneous optimisation of performance and dimensions that can be achieved through both approaches is unique and, for this reason, it is believed that the ideas presented in this work can be of actual interest in practical applications

Reduction of Electromagnetic Interference Susceptibility in Small-Signal Analog Circuits Using Complementary Split-Ring Resonators

Low-frequency analog and digital electronic circuits are susceptible to electromagnetic interference in the radiofrequency (RF) range. This disturbance is produced when the coupled RF signal is rectified by the nonlinear behavior of the semiconductors used in the small-signal analog input stage of the electronic system. Circuits based on operational amplifiers are usually employed for such input stages. These circuits present an amplitude modulation demodulation produced by the nonlinearity of internal transistors. Such a phenomenon generates demodulated signals in the low-frequency range. In this paper, this effect is suppressed by combining the conventional printed circuit board layout with complementary split-ring resonators (CSRRs). CSRRs are constitutive elements for the synthesis of metamaterials with negative effective permittivity, which are mainly excited to the host line by means of electric coupling. Electromagnetic simulations and experimental results show an effective rejection of the undesired RF demodulation effect with no extra cost in terms of the device area or manufacturing process.

Impact of NBTI on EMC behaviours of CMOS inverter

In this paper the Electromagnetic Robustness (EMR) of a CMOS inverter has been analyzed when the pFETs are submitted to negative bias temperature instability (NBTI). The impact of pFET and CMOS inverter has been experimentally quantified and the switching noise and electromagnetic susceptibility has been analyzed by means of simulation. The results show that NBTI reduces the switching noise whereas the EMI susceptibility is not modified.