Atsushi Sanada

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.

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.

A via-free microstrip left-handed transmission line

A via-free microstrip left-handed (LH) transmission line (TL) is proposed, which enables easy and low-cost fabrication of backward wave TLs. Based on the equivalent circuit, dispersion characteristics of the TL are theoretically obtained and the effect of the virtual short capacitance on the LH bandwidth is shown. The balanced/unbalanced CRLH criterion for seamless transition from the backward and forward wave propagation is also derived. The microstrip LH TL is implemented and the backward wave support is confirmed both by full-wave FEM simulations and experiments. A 38-cell TL exhibits a backward to forward scanning leaky-wave antenna capability.

An artificial dielectric material of huge permittivity with novel anisotropy and its application to a microwave BPF

Artificial dielectrics of very high equivalent permittivity are designed and fabricated by use of a patterned PCB printed circuit board. Rectangular metal patterns are etched out to attain as big a capacitance with each other as possible but as small a current as possible, which is important in order to realize large permittivity and small loss, respectively. Artificial dielectric disk resonators are created to excite the TE/sub 01/spl delta// mode selectively, aligning the rectangular metal patterns along the direction of the mode electric field lines. Thus, a miniaturized BPF with superior spurious characteristics is fabricated using three disk resonators.

A broadband left-handed (LH) coupled-line backward coupler with arbitrary coupling level

A novel broadband left-handed (LH) coupled-line backward coupler with arbitrary coupling level is presented. This coupler is composed of two LH transmission lines (TL) constituted of series interdigital capacitors and shunt shorted-stub inductors. A quasi-0dB implementation of the coupler is demonstrated by simulation and measurement results, and shown to exhibit a bandwidth of 35% despite the relatively wide lines-gap of 0.3mm. An even/odd modes analysis is presented to explain the working principle of the component. A 3dB-quadrature implementation, with 37% bandwidth, is also demonstrated. Finally, parametric results illustrate the versatility of the LH coupler and its strongly enhanced backward coupling compared with the conventional coupled-line coupler.

/spl lambda//4 stepped-impedance resonator bandpass filters fabricated on coplanar waveguide

Simple and compact multi-stage microwave bandpass filters (BPFs) using /spl lambda//4 stepped-impedance resonators (SIRs) fabricated on coplanar waveguide (CPW) are presented, which are applicable for MMICs or high-T/sub c/ superconducting filters. An accurate, tuning-free, design method of the /spl lambda//4 SIR-BPF is demonstrated with assistance of full-wave electromagnetic field simulator, which is based on a conventional filter design method using impedance inverters. Full-wave simulation and experimental results for a two-stage Chebyshev BPF designed at 5 GHz agreed well with theoretical results.

Novel Two-Dimensional Planar Negative Refractive Index Structure

A novel purely distributed two-dimensional (2D) planar structure with a negative refractive index (NRI) is proposed. The structure consists of a 2D periodic array of unit cells with metal patterns on the both sides of a substrate. The unit cell with the dimension of 5 x 5 mm 2 is designed at an operation frequency of about 5 GHz by full-wave finite element method simulations. Numerical simulations on the dispersion characteristics are carried out and NRI property of the structure is confirmed. A equivalent circuit taking into account the mutual capacitance between the adjacent ports in the unit cell is introduced, and theoretical investigations based on the equivalent circuit reveals that the anisotropy can be controlled by the mutual capacitance. A 10 x 20 unit-cell NRI material is fabricated and the NRI property has been confirmed experimentally in excellent agreement with Snells law.

Microwave circuits based on negative refractive index material structures

The paper presents the fundamentals of composite right/left-handed (CRLH) transmission lines and materials, and proposes an accurate circuit model of these structures for the design of practical applications. Three novel applications of CRLH meta-structures, developed at UCLA, are demonstrated: an arbitrary coupling-level backward-wave coupler, a zeroth order resonator and a distributed planar negative lens.

High Q or High Effective Permittivity Artificial Dielectric Resonator in a Waveguide

New strip arrangements for high Q or high effective permittivity are proposed for artificial dielectric resonators in a waveguide. The quality factor and the effective permittivity are discussed by changing strip arrangement composing the artificial dielectric. Concentrating strips from both sides to the middle in the waveguide leads to increase of unloaded Q. The value becomes high to several thousands by decreasing dielectric loss of the material. Interdigital strip arrangement makes the effective permittivity very high. A resonator of the strip arrangement has effective permittivity over 800 and unloaded Q over 1000. Moreover the resonator exhibits a good spurious characteristic with no unnecessary resonant mode throughout several harmonics range.

Dielectric Resonator Based on Artificial Dielectrics and its Application to a Microwave BPF

We propose an evaluation procedure of arificial dielectrics and a disk resonator of novel structure. The permittivity can be calculated by using a commercial software and simple equations. A disk resonator made of anisotropic artificial materials has mode selectivity. The resonator is applied to a bandpass filter.