Masahiro Akiyama

Dielectric-Resonator-Based Composite Right/Left-Handed Transmission Lines and Their Application to Leaky Wave Antenna

Propagation and radiation characteristics of 1-D dielectric-resonator-based composite right/left-handed metamaterial structures with open mesh plates are investigated as a function of configuration parameters. The complex effective permittivity and permeability are estimated from the scattering parameters of the unit-cell structure. Based on this configuration, the single-mode transmission line is designed and the backfire-to-endfire frequency-scanned leaky wave antenna is implemented. It is found from numerical simulations that the 30-cell leaky wave antenna has a gain of 10 dBi with a scanning angle of over 90deg covering backfire-to-endfire directions. The measurement results show as wide beam-steering angles as numerically predicted.

Nonreciprocal Phase-Shift Composite Right/Left Handed Transmission Lines and Their Application to Leaky Wave Antennas

A new type of nonreciprocal phase-shift transmission line is proposed; it realizes the dominant right-handed mode in one direction of the power flow along the line, and the dominant left-handed mode in the opposite power direction. These right and left handed modes can have the same wave number vector at a specific frequency but there is no significant coupling effect. An equivalent circuit model is provided to explain its nonreciprocal transmission characteristics. A nonreciprocal phase-shift composite right/left handed transmission line is designed to satisfy specific performance parameters and fabricated as a ferrite microstrip line. The leaky wave radiation characteristics of the fabricated nonreciprocal line are investigated. An experiment and analyses confirm obliquely unidirectional leaky wave radiation from the line for the two different directions of the transmitted power.

Nonreciprocal Phase-Shift Composite Right/Left Handed Microstrip Lines Using Ferrite-Rod-Embedded Substrate

Nonreciprocal phase-shift composite right/left handed transmission lines with small nonreciprocity in the amplitude of the transmission coefficients are proposed. The present structures are composed of a microstrip line periodically loaded with series capacitance and shunt inductance, and a ferrite rectangular rod is embedded in the dielectric substrate just below the center strip. The balanced composite right/left handed transmission line with nonreciprocal phase characteristics is designed. The numerical simulation results validate that the nonreciprocity in magnitude of the transmission coefficients is negligibly small whereas the nonreciprocity in the phase is still kept relatively large for the present configuration.

Anisotropic 3-D Composite Right/Left-Handed Metamaterial Structures Using Dielectric Resonators and Conductive Mesh Plates

New configuration of anisotropic 3-D composite right/left-handed (CLRH) metamaterial structures is proposed and designed. It is composed of stacked layers using conductive mesh plates and dielectric layers including 2-D array of dielectric resonators. Balanced CLRH transmission structures are designed not only for both polarization and propagation directions in the layer plane, but also for the normal propagation. The structure is essentially anisotropic and has significant polarization dependence for the wave propagation. Still, for the wave propagation with the polarization parallel to the mesh plates, it can provide relatively small anisotropic propagation characteristics in a certain frequency region if the configuration parameters are appropriately designed. Additionally, it is numerically confirmed that the designed structure shows the left-handedness for the in-plane propagation with the normal polarization, but not right-handedness. The negative-refractive-index flat lens is experimentally demonstrated for validation.

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.

Influence of reflected waves at a terminal of nonreciprocal phase-shift CRLH transmission lines on the leaky wave radiation

The influence of reflected waves at a terminal of a nonreciprocal phase-shift composite right/left handed transmission line on the leaky wave radiation is investigated. In the numerical simulation, the radiation characteristics for both a one-way propagation along the nonreciprocal phase-shift composite right/left handed transmission line and a propagation along the same line but with the reflected waves at the terminal are compared. The numerical results validate gain enhancement of the obliquely unidirectional leaky wave radiation by more than 3 dB due to additional radiation from the reflected waves.

Observation of near field distributions along a nonreciprocal phase-shift composite right/left handed transmission line

In this paper, near field distributions were experimentally observed along a NRCRLHTL using a magnetized ferrite medium. From the measured phase distributions, it was confirmed that there exists an operational frequency region where the dominant mode is right-handed in a propagation direction, and left-handed in the opposite propagation direction.

Measurement of the surface resistance of conductive textiles at microwave frequency

Textile samples which consist of conductive threads are characterized in a microwave frequency range. The configurations of the threads used in this study are traditional ones which have no metallic wires or filaments and have been used in decoration in clothing for hundred years. A half-wavelength microstrip line resonator is fabricated and the Q factors are measured for a copper strip line and for the strip of sample textile from the frequency responses. Difference of Q factors in the two cases leads to the relationship between the surface resistances of the sample and a copper sheet. Then the surface resistances of the samples as conductive sheets are listed and compared. It is found that the relative resistivity is less than four for some textiles. These conductive textiles using a traditional technology are expected to use in wearable electrical systems.

Influence of the coupling between a cavity and a transmission line on the measurement of complex permittivity by the resonant cavity perturbation method

The real part of permittivity can be evaluated at 2.247 GHz by the resonant cavity perturbation method in strong coupling state up to -3.7 dB of coupling that has not been investigated. The imaginary part of the permittivity can be evaluated reliably up to -14 dB of coupling. In the resonant cavity perturbation method, the influence of the coupling on blank and sample loaded cavity are compensated up to -14 dB of |S21|. The possibility of measuring high loss materials was shown by the measurement of Au coated ceramic rod.

RZ pulse-width dependence of impulse radio UWB over combined fiber and wireless link

We demonstrated the dependence of IR-UWB signal waveform on the RZ pulse width, and made it clear that optical RZ pulse width of 12.5 to 90 ps is necessary in combined 1.25 Gbps 10 km SMF and wireless link with UWB band of 7.25–10.25GHz. The 10Gbps (1.25 Gbps × 8TDM) IR signal transmission in optical fiber link is also demonstrated using 29 ps optical pulse. The system satisfies the communication quality in the wireless transmission range of 0.5 m–2.5 m.