Metamaterial Lines Research Articles

Symmetric surface waves along a metamaterial dielectric waveguide and a perfectly conducting cylinder covered by a metamaterial layer


 
 
 Existence of symmetric complex waves in a metamaterial dielectric rod and a perfectly conducting cylinder of circular cross section covered by a concentric layer of metamaterial, a metamaterial Goubau line, is proved. Analytical investigation and numerical solution of dispersion equations reveal several important properties of running waves inherent to open metal-metamaterial waveguides which have not been reported for waveguides filled with standard media.
 
 

A Compact Reconfigurable NRI-TL Metamaterial Phase Shifter for Antenna Applications

This communication presents a compact reconfigurable phase shifter based on negative-refractive-index transmission-line (NRI-TL) metamaterial unit cells. Two interswitchable NRI-TL metamaterial unit cells are collocated within the same board area, and can be reconfigured based on the biasing polarity of embedded p-i-n diodes to provide two discrete phase states. The p-i-n diodes are located on the shunt branches of the metamaterial line in order to reduce losses in the direct signal path. Design limitations in terms of return loss and insertion loss are discussed in relation to the two phase states. A proof-of-concept module with a size of $17.8 \times 21.6~ \text {mm}^{2}$ is designed at 1 GHz, with measured insertion phases of −14.5° and +58.5° in the two phase states leading to a differential phase shift of 73°, while exhibiting insertion losses of 1.43 and 0.89 dB, respectively. The combined bandwidth for which the reflection coefficient in both states remains simultaneously below −10 dB is 0.46 GHz (46%), from 0.83 to 1.29 GHz.

Enhancement of Phase-Shifting Nonreciprocity in Microstrip-Line-Based Metamaterials by Using a Combination of Their Curvatures and Asymmetrical Insertion of Stubs

A new approach to enhance the phase-shifting nonreciprocity of microstrip-line-based metamaterials with normally magnetized ferrite substrates is proposed, by using a combination of curvature of the lines and asymmetric insertion of stubs. In the analytical approach, the nonreciprocity is approximately formulated by introducing asymmetric surface admittance on the side walls at the strip edges, showing that a linear combination of two factors due to the line curvature and the difference of asymmetric admittances contributes to geometrical asymmetry of the wave-guiding structures. Numerical simulation and measurement results verify predictions from the analytical approach. It is demonstrated that a combination of larger curvature of the metamaterial lines and hybrid insertion of inductive and capacitive stubs on the inner and outer sides, respectively, provides significant enhancement of the nonreciprocity compared to the single side insertion of stubs.

Efficient energy transfer through a bifilar metamaterial line connecting microwave waveguides

Microwave waveguides allow an effective transfer of electromagnetic energy through straight connection or well-rounded curves, but become rather inefficient in case of sharp bends or squeezed waveguide cross-sections. Here, we discuss the possibility to funnel the electromagnetic energy propagating in a waveguide through arbitrarily curved narrow channels hosting a metamaterial-inspired structure able to convert the propagating mode of the waveguide in an electric signal, and vice versa. We show experimentally how sharp bends can be inserted within these propagation channels of arbitrary lengths without introducing significant insertion losses. In particular, efficient energy funneling in 90°-, 180°-, and “S”-shaped bends are numerically and experimentally verified. The proposed reflectionless waveguide bends may find applications in modern radar and antenna systems, where the demand for space and weight reduction of the electromagnetic circuitry is ever growing.

Experimental Verification of Below-Cutoff Propagation in Miniaturized Circular Waveguides Using Anisotropic ENNZ Metamaterial Liners

This paper presents experimental verification of below-cutoff transmission through miniaturized waveguides whose interior is coated with a thin anisotropic metamaterial liner possessing epsilon-negative and near-zero (ENNZ) properties. These liners are realized using a simple, printed-circuit implementation based on inductively loaded wires, and introduce an HE$_{11}$ mode well below the natural cutoff frequency. The inclusion of the liner is shown to substantially improve the transmission between two embedded shielded-loop sources. A homogenization scheme is developed to characterize the liner's anisotropic effective-medium parameters, which is shown to accurately describe a set of frequency-reduced cutoffs. The fabrication of the lined waveguide is discussed, and the experimental and simulated transmission results are shown to be in agreement.

New approach for extraordinary transmission through an array of subwavelength apertures using thin ENNZ metamaterial liners.

Extraordinary transmission (ET) through a periodic array of subwavelength apertures on a perfect metallic screen has been studied extensively in recent years, and has largely been attributed to diffraction effects, for which the periodicity of the apertures, rather than their dimensions, dominates the response. The transmission properties of the apertures at resonance, on the other hand, are not typically considered 'extraordinary' because they may be explained using more conventional aperture-theoretical mechanisms. This work describes a novel approach for achieving ET in which subwavelength apertures are made to resonate by lining them using thin, epsilon-negative and near-zero (ENNZ) metamaterials. The use of ENNZ metamaterials has recently proven successful in miniaturizing circular waveguides by strongly reducing their natural cutoff frequencies, and the theory is adapted here for the design of subwavelength apertures in a metallic screen. We present simulations and proof-of-concept measurements at microwave frequencies that demonstrate ET for apertures measuring one-quarter of a wavelength in diameter and suggest the potential for even more dramatic miniaturization simply by engineering the ENNZ metamaterial dispersion. The results exhibit a fano-like profile whose frequency varies with the properties of the metamaterial liner, but is independent of period. It is suggested that similar behaviour can be obtained at optical frequencies, where ENNZ metamaterials may be realized using appropriately arranged chains of plasmonic nanoparticles.

Experimental and Numerical Investigation of Termination Impedance Effects in Wireless Power Transfer via Metamaterial

This paper presents an investigation of the transmitted power in a wireless power transfer system that employs a metamaterial. Metamaterials are a good means to transfer power wirelessly, as they are composed of multiple inductively-coupled resonators. The system can be designed and matched simply through magneto-inductive wave theory, particularly when the receiver inductor is located at the end of the metamaterial line. However, the power distribution changes significantly in terms of transmitted power, efficiency and frequency if the receiver inductor slides along the line. In this paper, the power distribution and transfer efficiency are analysed, studying the effects of a termination impedance in the last cell of the metamaterial and improving the system performance for the resonant frequency and for any position of the receiver inductor. Furthermore, a numerical characterisation is presented in order to support experimental tests and to predict the performance of a metamaterial composed of spiral inductor cells with very good accuracy.

Miniaturized Circular-Waveguide Probe Antennas Using Metamaterial Liners

This work presents the radiation performance of open-ended circular-waveguide probe antennas that have been miniaturized by the introduction of thin metamaterial liners. The liners introduce an HE$_{11}$ mode well below the natural cutoff frequency, which provides substantial gain improvements over a similarly sized waveguide probe. A new feeding arrangement employing a shielded-loop source embedded inside the miniaturized waveguide is developed to efficiently excite the HE$_{11}$ mode and avoid the excitation of other modes across the frequency reduced band while maintaining the antenna's compactness. A metamaterial-lined circular-waveguide probe antenna operating over 42% below its natural cutoff frequency is designed to provide a radiation efficiency of up to 28.8%. A simple, printed-circuit implementation of the metamaterial liner based on inductively loaded wires is proposed and its dispersion features are discussed.

Isolation Circuits Based on Metamaterial Transmission Lines for Multiplexers(Invited Paper)

Multiplexers based on isolation circuits made of metamaterial lines are proposed and studied. The new approach provides unique advantageous features beneficial to system designer. For instance, there is no need to modify the filters used in multiplexers. Also, the design process is straightforward. In this paper, two types of multiplexers based on metamaterial isolation circuits are presented, and their operation concepts are explained. Also, theories and design process of isolation circuits are presented to help readers design and fabricate proposed multiplexers. For verifying the concepts, two types of triplexers and two types of quadruplexers are designed and fabricated. All filters used in the multiplexers are commercial surface acoustic wave filters. The measured results are well matched with the simulation results.

Below-Cutoff Propagation in Metamaterial-Lined Circular Waveguides

This paper investigates the propagation characteristics of circular waveguides whose interior surface is coated with a thin metamaterial liner possessing dispersive, negative, and near-zero permittivity. A field analysis of this system produces the dispersion of complex modes, and reveals in detail intriguing phenomena such as backward-wave propagation below the unlined waveguide's fundamental-mode cutoff, resonant tunneling of power, field collimation, and miniaturization. It is shown how the waveguide geometry and metamaterial parameters may be selected to engineer the lined waveguide's spectral response. Theoretical dispersion and transmission results are closely validated by full-wave simulations.

Demonstration of an Octave-Bandwidth Negligible-Loss Metamaterial Horn Antenna for Satellite Applications

This paper reports on the detailed design and experimental demonstration of a metamaterial-enabled low-sidelobe horn antenna (metahorn) based on principles similar to those of earlier soft horn antennas. The target application is a linearly polarized feed horn in the super-extended C-band (3.4-6.725 GHz) for communication satellite reflector antennas. The paper describes the detailed design and manufacturing of the -plane metamaterial liner (metaliner) based on a freestanding wire grid without the need for a dielectric substrate material. The measured copolarized and cross-polarized antenna patterns from the feed horn demonstrate over an octave pattern bandwidth with negligible loss. The results show similar bandwidth with lower sidelobes and backlobes than those of the trifurcated horn that is currently used as the standard C-band feed for single linear polarization. This demonstration shows promise for lightweight metamaterial horns to replace heavy and expensive C-band corrugated horns.

Topology optimization of multilayer left-handed material based on the genetic algorithm

Owing to the special properties, left-handed materials (LHM) have important potential applications in engineering. However, in the current stage, the design of LHM is primarily based on several basic prototypes such as meta-material and transmission line structures. In the present work, the topology optimization technology is introduced to design a type of multilayer LHM. A type of one-dimensional material with periodic unit cell is studied and the topology of its microstructure is designed by using the technology of enumerative search and genetic algorithm (GA), respectively. The material is composed of metal and ferrite films, and several types of negative refraction materials are obtained numerically. These obtained materials with periodic unit cells can exhibit negative refractive index in some frequency spectrums, and the results show that the GA could achieve good designs efficiently in a larger design space.

COMPACT COPLANAR WAVEGUIDE (CPW)-FED TUNABLE WIDEBAND RESONANT ANTENNAS USING METAMATERIAL TRANSMISSION LINE

A wideband resonant antenna loaded with coplanar waveguide (CPW) epsilon negative transmission metamaterial line (ENG MTL) unit cells is proposed. The CPW geometry provides high design freedom, and the metamaterial resonant antenna is designed on a CPW single layer where vias are not required. The novel ENG unit cell on a vialess single layer simplifles the fabrication process. The dispersion analysis of the metamaterial unit cell reveals that increasing right hand capacitance and left hand inductance can decrease the half-wavelength resonance frequency, thus reducing the electrical size of the proposed antenna. Based on the proposed ENG MTL unit cell, the wideband antenna is verifled by a commercial EM simulator HFSS11 and developed. Comparing the measured performances with those resonant antennas, it is noticed that the proposed antenna achieves high bandwidth and further size reduction, higher e-ciency and easier manufacturing. The realized antenna has a compact size of 0:32‚0£0:20‚0£0:012‚0 (26:6mm£16:mm£1mm) at 3.65GHz, and operates over the frequency ranges 3.38{4.23GHz suitable for WiMAX applications. Good agreement between the simulated and measured results is obtained.

Review of Soft and Hard Horn Antennas, Including Metamaterial-Based Hybrid-Mode Horns

This paper is divided into three parts. Part one gives an overview of the early history of the design and implementation of hard horn antennas, and of the concept formulation of soft and hard electromagnetic surfaces. Part two presents a review of all known classes of soft and hard hybrid-mode horns. Part three presents a new class of hybrid-mode horns, based on the use of a low-index metamaterial liner on the wall. Moment-Method analysis of both soft and hard metamaterial horns indicates that it may be feasible to realize these horns with very large bandwidth. This is because the desired (analyzed) metamaterial dispersion is similar to the Drude dispersion curve (monotonically increasing permittivity as a function of frequency), which represents typical electromagnetic dispersion in dense media. A successful implementation of these horns depends on whether low-index metamaterials can be implemented with polarization-independent boundary impedance, favorable dispersion characteristics, and reasonable loss, mass, and production cost.

Metamaterial-based wideband rat-race hybrid coupler using slow wave lines

Based on derived convenient design equations for slow wave transmission lines and metamaterial line, a very compact and wideband rat-race hybrid coupler is proposed using three -90° slow wave lines and one -90° metamaterial line. The closed-form solutions for circuit parameters based on both phase and phase slope matching conditions are derived. At the design frequency of 2 GHz, the size of the proposed coupler is about 2.0 × 2.0 cm, which is a 85% reduction compared with the conventional one. In addition, the phase balance bandwidths based on ∠ S 21 -∠ S 31 (0±10°) and ∠ S 24 -∠ S 34 (180±10°) have been found to be 150 and 125%, which are 1.8 and 3.0 times improvements compared with those of the conventional one. The measured results are in reasonable agreement with the circuit- and EM-simulated ones.

Design of generalised negative-refractive-index transmission lines for quad-band applications

A design procedure is presented for synthesising artificial transmission lines (metamaterial lines) that exhibit four alternating backward (left-handed) and forward (right-handed) bands. Specifically, analytic expressions are given that directly yield the loading lumped elements needed for synthesising a desired Bloch phase at four specified frequencies and at a specified Bloch impedance level. This procedure becomes useful for designing structures such as dual-band periodic leaky-wave antennas, dual-band/quad-band negative-index lenses, as well as quad-band microwave passive components and resonant antennas.

Low-Profile Folded Monopoles With Embedded Planar Metamaterial Phase-Shifting Lines

This paper presents the analysis, design and measurement of novel, low-profile, small-footprint folded monopoles employing planar metamaterial phase-shifting lines. These lines are composed of fully-printed spiral elements, that are inductively coupled and hence exhibit an effective high- mu property. An equivalent circuit for the proposed structure is presented, validating the operating principles of the antenna and the metamaterial line. The impact of the antenna profile and the ground plane size on the antenna performance is investigated using accurate full-wave simulations. A lambda/9 antenna prototype, designed to operate at 2.36 GHz, is fabricated and tested on both electrically large and small ground planes, achieving on average 80% radiation efficiency, 5% (110 MHz) and 2.5% (55 MHz) -10 dB measured bandwidths, respectively, and fully omnidirectional, vertically polarized, monopole-type radiation patterns.

Impulse regime CRLH resonator for tunable pulse rate multiplication

A novel tunable microwave broadband resonator, inspired from optical laser systems, is presented. In contrast to usual harmonic resonators, the proposed device is based on broadband composite right/left handed metamaterial lines. This line, configured as a resonator, provides nonuniform spectral resonances due to the nonlinear nature of its dispersion curve. This is exploited in the impulse regime, where the input pulse spectrum is discretized inside the resonator, with different spectral separation as a function of the carrier frequency. This discretization leads to a pulse periodicity in time, with a tunable output time period. On the basis of the new broadband resonator features, a pulse rate multiplication device is proposed. This device provides an increase in the repetition rate of a periodic input pulse, with the additional advantage of repetition rate tunability.

Tunable bandpass filter based on capacitor-loaded metamaterial lines

A bandpass filter is constructed by loading a left-handed metamaterial transmission line with an additional shunt capacitor. The shunt capacitor provides more freedom to control the passband characteristics of the resulting metamaterial line. A bandpass filter is designed with a centre frequency that is tunable from 0.45 to 0.65 GHz.

Compact Rat-Race Hybrid Coupler Using Slow Wave and Left-Handed Transmission Lines

Based on provided convenient design equations for slow wave transmission lines and metamaterial line, a very compact rat-race hybrid coupler is proposed using three slow wave lines and one metamaterial line. At the design frequency of 2GHz, the size of the proposed coupler is 2.3cm × 2.7cm, which is a 74% reduction compared with the conventional one. Despite the considerable size reduction, the theoretical bandwidths based on |S11|, |S31|, ∠S21-∠S31, and ∠S24-∠S34, have been improved by 9%, 7%, 31%, and 59%, respectively. The measured performances are in reasonable agreement with the theoretical ones.