Christophe Caloz

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.

Leaky-Wave Antennas

This paper gives a basic review and a summary of recent developments for leaky-wave antennas (LWAs). An LWA uses a guiding structure that supports wave propagation along the length of the structure, with the wave radiating or “leaking” continuously along the structure. Such antennas may be uniform, quasi-uniform, or periodic. After reviewing the basic physics and operating principles, a summary of some recent advances for these types of structures is given. Recent advances include structures that can scan to endfire, structures that can scan through broadside, structures that are conformal to surfaces, and structures that incorporate power recycling or include active elements. Some of these novel structures are inspired by recent advances in the metamaterials area.

A novel composite right-/left-handed coupled-line directional coupler with arbitrary coupling level and broad bandwidth

A novel composite right-/left-handed (CRLH) backward-wave coupled-line directional coupler with arbitrary coupling level and broad bandwidth is presented, explained by even/odd-mode analysis, validated by full-wave simulations, and demonstrated by experiments. First, the CRLH-transmission-line (CRLH TL) theory is given, and a microstrip implementation of a CRLH TL is described. A simple circuit model is then proposed both for the understanding and design of the coupler. The coupler exhibits very unusual characteristics, such as zero electrical length, imaginary even/odd-mode characteristic impedances, and coupling dependence on even/odd attenuation length (instead of propagation length). Both a quasi-0and 3-dB coupler are demonstrated experimentally. The 3-dB coupler exhibits amplitude balance of /spl plusmn/2 dB over a huge bandwidth of 50% (3.5-5.8 GHz), phase balance of 90/spl deg//spl plusmn/5/spl deg/ from 3.0 to 4.0 GHz and directivity of 20 dB.

Arbitrary dual-band components using composite right/left-handed transmission lines

Arbitrary dual-band microstrip components using composite right/left-handed (CRLH) transmission lines (TLs) are presented. Theory, synthesis procedure, and implementation of the dual-band quarter-wave (/spl lambda//4) CRLH TL are presented. Arbitrary dual-band operation is achieved by the frequency offset and the phase slope of the CRLH TL. The frequency ratio of the two operating frequencies can be a noninteger. The dual-band /spl lambda//4 open/short-circuit stub, dual-band branch-line coupler (BLC), and dual-band rat-race coupler (RRC) are also demonstrated. The performances of these dual-band components are demonstrated by both simulated and measured results. Insertion loss is larger than 23 dB for the shunt /spl lambda//4 CRLH TL open-circuit stub and less than 0.25 dB for the shunt /spl lambda//4 CRLH TL short-circuit stub at each passband. The dual-band BLC exhibits S/sub 21/ and S/sub 31/ larger than -4.034 dB, return losses larger than 17 dB, isolations larger than 13 dB, phase differences 90/spl deg//spl plusmn/1.5/spl deg/, and gain imbalance less than 0.5 dB at each passband. The dual-band RRC exhibits S/sub 21/ and S/sub 31/ larger than -4.126 dB, return losses larger than 12 dB, isolations larger than 30 dB, phase difference 180/spl deg//spl plusmn/4/spl deg/, and gain imbalance less than 0.2 dB at each passband.

Metamaterial-based electronically controlled transmission-line structure as a novel leaky-wave antenna with tunable radiation angle and beamwidth

A metamaterial-based electronically controlled transmission-line structure is presented and demonstrated as a novel leaky-wave (LW) antenna with tunable radiation angle and beamwidth functionalities. This structure is, in essence, a composite right/left-handed (CRLH) microstrip structure incorporating varactor diodes for fixed-frequency voltage-controlled operation. Angle scanning at a fixed frequency is achieved by modulating the capacitances of the structure by adjusting the (uniform) bias voltage applied to the varactors. Beamwidth tuning is obtained by making the structure nonuniform by application of a nonuniform bias voltage distribution of the varactors. A rigorous analysis based on an extension of the CRLH concept is proposed and the corresponding dispersion curves, obtained by equivalent-circuit formulas with LC parameters extracted from full-wave simulation, are shown. A 30-cell LW antenna structure, incorporating both series and shunt varactors for optimal impedance matching and maximal tuning range, is designed. This prototype exhibits continuous scanning capability from 50/spl deg/ to -49/spl deg/ by tuning the bias voltages from 0 to 21 V at 3.33 GHz. A maximum gain of 18 dBi at broadside is also achieved. In addition, it provides half-power beamwidth variation of up to 200% with comparison to the case of uniform biasing. The effect of intermodulation due to the nonlinearity of the varactors is shown to be negligible for antenna applications. The antenna is tested in a 10-Mb/s binary phase-shift keying transmission link and successful recovery of the baseband data is demonstrated.

Transmission line approach of left-handed (LH) materials and microstrip implementation of an artificial LH transmission line

A transmission line (TL) approach of left-handed (LH) materials is proposed. The transmission characteristics of an ideal LH-TL are presented, the constitutive parameters of an equivalent LH material are derived and shown to be negative, and some LH-transmission paradoxes are explained. Next, a method to design an artificial LH-TL in the form of an ideal lumped-elements ladder network is described and illustrated with simulation results. It is shown that, in this line, left-handedness can be achieved without losses over an unlimited bandwidth, from the cutoff of the resulting high-pass filter to infinity, with excellent agreement with theory. Finally, a microstrip implementation of the LH line for microwaves, using interdigital capacitors and stub inductors, is demonstrated, with moderate insertion loss and a broad bandwidth of the order of 100%.

Novel microwave devices and structures based on the transmission line approach of meta-materials

This paper is composed of two parts. In the first part, the fundamentals of ideal transmission lines (TL) meta-materials (NM) with their physical characteristics and the synthesis of practical artificial TL-MMs with their circuital characteristics are presented. A microstrip implementation of a composite right/left handed (CRLH) TL is shown. In the second part, several novel applications based on the theory of the first part are demonstrated: a backfire-to-endfire leaky wave antenna, a coupled-line coupler with arbitrary coupling, a compact enhanced-bandwidth hybrid ring, a dual-band inharmonic branch-line coupler and a negative reflection/refraction phase-conjugating array interface.

Planar distributed structures with negative refractive index

Planar distributed periodic structures of microstrip-line and stripline types, which support left-handed (LH) waves are presented and their negative refractive index (NRI) properties are shown theoretically, numerically, and experimentally. The supported LH wave is fully characterized based on the composite right/left-handed transmission-line theory and the dispersion characteristics, refractive indexes, and Bloch impedance are derived theoretically. In addition, formulas to extract equivalent-circuit parameters from full-wave simulation are given. Open (microstrip) and closed (stripline) structures with a 5/spl times/5 mm/sup 2/ unit cell operating at approximately 4 GHz are designed and characterized by full-wave finite-element-method simulations. A 20 /spl times/ 6 unit-cell NRI lens structure interfaced with two parallel-plate waveguides is designed. The focusing/refocusing effect of the lens is observed by both circuit theory and full-wave simulations. Focusing in the NRI lens is also observed experimentally in excellent agreement with circuit theory and numerical predictions. This result represents the first experimental demonstration of NRI property using a purely distributed planar structure.

CRLH metamaterial leaky-wave and resonant antennas

Composite right-/left-handed (CRLH) transmission-line (TL) metamaterials, with their rich dispersion and fundamental right-/left-hand duality, represent a paradigm shift in electromagnetics engineering and, in particular, for antennas. This paper presents an overview of the most practical leaky-wave and resonant CRLH antennas, which all exhibit functionalities or/and performance superior to prior state of the art. The leaky-wave antennas provide full-space dynamic scanning capability, with fan beams, conical beams in uni-planar configurations, pencil beams without any complex feeding network, and actively shaped beams based on the concept of aperture digitization. The resonant antennas offer alternative properties and a solution to beam-squinting when no scanning is required, including multi-band (dual/tri-band) operation, zeroth-order high efficiency, high directivity, and planar electric and magnetic monopole radiators.

A compact enhanced-bandwidth hybrid ring using an artificial lumped-element left-handed transmission-line section

A new type of compact enhanced-bandwidth hybrid ring using an artificial lumped-element left-handed (LH) transmission-line (TL) section is proposed. The replacement of the 270/spl deg/ branch of the conventional hybrid ring by a -90/spl deg/ LH-TL branch results in both size reduction and bandwidth enhancement. The working principle of the LH TL used in the hybrid ring is explained and the performances of the component are demonstrated by measurement results. The proposed hybrid exhibits 67% size reduction compared to the conventional one, and shows a 58% and 49% bandwidth enhancements at 2 GHz in the 180/spl deg/-out-of-phase and in-phase operations, respectively.