Anthony Lai

Composite right/left-handed transmission line metamaterials

Metamaterials are artificial structures that can be designed to exhibit specific electromagnetic properties not commonly found in nature. Recently, metamaterials with simultaneously negative permittivity (/spl epsiv/) and permeability (/spl mu/), more commonly referred to as left-handed (LH) materials, have received substantial attention in the scientific and engineering communities. The unique properties of LHMs have allowed novel applications, concepts, and devices to be developed. In this article, the fundamental electromagnetic properties of LHMs and the physical realization of these materials are reviewed based on a general transmission line (TL) approach. The general TL approach provides insight into the physical phenomena of LHMs and provides an efficient design tool for LH applications. LHMs are considered to be a more general model of composite right/left hand (CRLH) structures, which also include right-handed (RH) effects that occur naturally in practical LHMs. Characterization, design, and implementation of one-dimensional and two-dimensional CRLH TLs are examined. In addition, microwave devices based on CRLH TLs and their applications are presented.

Infinite Wavelength Resonant Antennas With Monopolar Radiation Pattern Based on Periodic Structures

The analysis of resonant-type antennas based on the fundamental infinite wavelength supported by certain periodic structures is presented. Since the phase shift is zero for a unit-cell that supports an infinite wavelength, the physical size of the antenna can be arbitrary; the antennas size is independent of the resonance phenomenon. The antennas operational frequency depends only on its unit-cell and the antennas physical size depends on the number of unit-cells. In particular, the unit-cell is based on the composite right/left-handed (CRLH) metamaterial transmission line (TL). It is shown that the CRLH TL is a general model for the required unit-cell, which includes a nonessential series capacitance for the generation of an infinite wavelength. The analysis and design of the required unit-cell is discussed based upon field distributions and dispersion diagrams. It is also shown that the supported infinite wavelength can be used to generate a monopolar radiation pattern. Infinite wavelength resonant antennas are realized with different number of unit-cells to demonstrate the infinite wavelength resonance

The challenge of homogenization in metamaterials

The problem of homogenization, i.e. substantial reduction of the electrical size of the average lattice constant, of electromagnetic left-handed (LH), or more generally composite right/left-handed (CRLH) metamaterials (MTMs), is presented. The undesirable effects of an electrical very large structural unit cell are explained and illustrated by full-wave simulations and experiments with CRLH mushroom structures. These effects are limited bandwidth, anisotropy, poor refraction due to coupling of the fundamental wave with space harmonics and diffraction at interfaces with other media. Transmission line method (TLM) simulations demonstrate that homogenization may mitigate or suppress these parasitic effects. In addition, the challenging necessity of drastically increasing inductances and capacitances in the homogenization process is demonstrated for CRLH MTMs.

Demonstration of Negative Refraction in a Cutoff Parallel-Plate Waveguide Loaded With 2-D Square Lattice of Dielectric Resonators

A 2D negative-refractive index metamaterial is proposed and investigated, which is composed of a parallel-plate waveguide loaded with a square lattice of disc-type dielectric resonators. Collective and macroscopic behavior of the dielectric resonator lattice under the fundamental TE resonance gives negative effective permeability, whereas the parallel-plate waveguide below the cutoff for TE modes provides negative effective permittivity. Thus, the double-negative condition for the propagated waves with the appropriate polarizations can establish the left-handedness. Equivalent-circuit models are shown to give a good insight into the physical mechanism of the guided waves. Numerical simulation of the 2D dispersion diagram verifies the existence of the left-handed (LH) guided modes along with the isotropic characteristics. A triangular prism of the proposed LH structure that is sandwiched by the right-handed parallel-plate waveguides is designed and fabricated to directly observe the negative refractive index of the LH waveguide. The numerical and experimental results validate the negative refraction for the proposed structure.

Negative Refraction in a Cut-Off Parallel-Plate Waveguide Loaded with Two-Dimensional Lattice of Dielectric Resonators

A two-dimensional (2D) negative-refractive-index metamaterial is proposed, which is composed of a parallel-plate waveguide and a square lattice of dielectric resonators (DR) inserted in it. The collective and macroscopic behavior of the DR lattice under TE resonance gives negative effective permeability whereas the parallel-plate waveguide below the cut-off for fundamental TE modes shows negative effective permittivity, which leads to the left-handedness. The 2D triangular prism of the proposed left-handed waveguide that is sandwiched by right-handed parallel-plate waveguides provides the numerical and experimental demonstrations of the negative refraction for the propagated waves

Wave interactions in a left-handed mushroom structure

Metamaterials and, in particular, left-handed (LH) materials (negative refractive index metamaterials) have drawn considerable attention in the physics and engineering communities over the last five years. This paper presents a synthesis of the refractive characteristics of a mushroom structure, including dispersion diagram, fields distributions, isotropy and refractive index. In addition, it introduces and demonstrates the concept of plane wave to cylindrical wave transformation by way of a parabolically curved RH/LH interface. A practical mushroom implementation of this interface is also discussed.

Integrated mixer based on composite right/left-handed leaky-wave antenna

This paper presents a novel balanced mixer receiver front-end design based on a metamaterial structure applicable to differential-/common-mode excitation. This metamaterial structure functions as a leaky-wave antenna and provides intrinsic common-mode suppression. Low LO leakage and high RF to LO isolation are achieved without additional filters for the LO and RF paths. The metamaterial is based on a unit-cell which under a differential-mode excitation behaves like a composite right/left-handed (CRLH) metamaterial. In contrast, the metamaterial unit-cell is below cut-off under a common-mode excitation. Experimental results are used to verify the proposed metamaterial’s differential-/common-mode characteristics. The metamaterial is integrated with a balanced mixer design resulting in an operation frequency range of 1.96 GHz – 2.40 GHz with an optimum mixer conversion loss of 21.1 dB at 2.4 GHz.

Leaky-Wave Steering in a Two-Dimensional Metamaterial Structure Using Wave Interaction Excitation

A two-dimensional composite right/left-handed (CRLH) metamaterial with an orthogonal feeding structure is demonstrated. By varying the magnitude of the input power to two orthogonal edges of the metamaterial, the net power flow direction can be controlled based on wave interaction. The CRLH metamaterial is analyzed and designed in terms of its equivalent circuit model and full-wave verification. The leaky-wave radiation from this metamaterial can be used for two-dimensional scanning without phase-shifters. Azimuth scanning is achieved by varying the magnitude of the input power at the two orthogonal edges of the structure, while elevation scanning is made possible by varying the operational frequency. Experimental radiation patterns of the metamaterial are shown and demonstrate an elevation scanning range of -61deg to +60deg and an azimuth scanning range of 0deg to +90deg with orthogonal two-edge feeding

Quasi-optical manipulations of microwaves using metamaterial interfaces

Novel microwave lenses are presented which are realized by interfacing a right-handed (RH) material with a left-handed (LH) material. The conic LH/RH interfaces required to realize LH lenses are presented. A novel parabolic refractor based on the composite right/left-handed (CRLH) metamaterial is also experimentally demonstrated

2.5-D stacked composite right/left-handed metamaterial structures using dielectric resonators and parallel mesh plates

In this paper, stacked structures composed of mesh plates and dielectric layers including 2-D array of dielectric discs are proposed as a new type of volumetric composite right/left-handed metamaterial structure for TE-polarized waves. No band gap condition between right and left-handed bands is designed in order to broaden the left-handed bandwidth by adjusting the aperture size of the mesh. Based on this layered metamaterial structure, a flat focusing lens which operates in free space is designed and fabricated. For a source launched from a small loop antenna, beam focusing through the fabricated finite-cell-layered lens is experimentally confirmed by measuring the field profiles.