Ikuo Awai

Microwave Characteristics of TiO2-Bi2O3 Dielectric Resonator

The microwave characteristics of the binary-system TiO2-Bi2O3 ceramics, which is widely known to exhibit a comparatively high dielectric constant in the lower-frequency band, are investigated from a new standpoint. It is shown in this article that the composition of 0.919TiO2-0.081Bi2O3 has a high dielectric constant (er=80), high Q (1800 at 5 GHz) and low temperature coefficient of resonant frequency (τf=+21 ppm/°C). From the X-ray diffraction and X-ray microanalysis, it is indicated that the crystal structure of this material is composed of two phases, TiO2 and Bi2Ti4O11, which possess a high er with a negative temperature coefficient and a high er with a positive temperature coefficient, respectively. The measurements of linear thermal expansion and temperature coefficient of capacitance are also carried out in order to study the behavior of temperature compensation in this system.

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.

Equivalent-circuit representation and explanation of attenuation poles of a dual-mode dielectric-resonator bandpass filter

A /spl lambda//4 rectangular-waveguide resonator of square cross section filled with high-permittivity ceramics has two degenerate lowest modes. A dual-mode bandpass filter based on this structure is studied, focusing on the attenuation poles at both sides of the passband. It is described how to achieve capacitive and inductive coupling between dominant modes of a resonator of square cross section. An equivalent-circuit model is proposed, including mode coupling, excitation from the external circuit, and direct coupling between input/output (I/O) electrodes. Equivalent-circuit parameters are measured and their validity is verified using simulated results. Appearance and annihilation of the attenuation poles are successfully explained by the proposed model, and attenuation pole frequencies are controlled by shifting the I/O electrode transversely.

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.

/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.

Influence of Rare Earth Ions on BaO-TiO2-Rare Earth Oxide Ceramics for Microwave Applications

The dielectric ceramic materials, 0.143BaO-0.714TiO2-0.143 rare earth oxides (REOx), have unique dielectric properties at microwave frequencies, which depend on the rare earth element (RE=Pr, Nd, Sm). In order to study the effect of the rare earth ions on dielectric properties, infrared reflection spectra of these ceramics were measured from 50 to 4000 cm-1 at room temperature. These data were analyzed according to the model proposed by Gervais and Piriou. Also, the fourth-order dielectric constants of these materials were estimated for the purpose of investigating the relationship between the dielectric loss and the anharmonic terms in the potential energy.

Applications of the finite difference techniques to the compensated VIP 3 dB directional coupler

A new and simple compensated structure for a vertically installed planar (VIP) 3 dB directional coupler has been studied theoretically as well as experimentally by combining an improved 2-D-general finite difference (2-D-GFD) design procedure with a three-dimensional finite difference time domain (3-D-FDTD) method. The obtained full wave analysis results agree well with the measured ones. The investigations have shown that with this planar compensated structure, a better performance of the VIP coupler in the L-band can be realized by only using the same kind of dielectric substrate for its vertical and horizontal one.

Resonant frequency and quality factors of a silver-coated /spl lambda//4 dielectric waveguide resonator

In this paper, resonant frequency, radiation loss, conductor loss, and dielectric loss of a silver-coated /spl lambda//4 dielectric waveguide resonator are investigated. Leakage of the electromagnetic field from the open-end face of the resonator is the only source of radiation, which also affects the resonant frequency. New theoretical expressions are devised to calculate resonant frequency, conductor quality (Q) factor, dielectric Q factor, and radiation Q factor. Effective conductivity of the silver-coated resonator is estimated from experimental unloaded Q factor. The theoretical analysis is validated by the experimental result and the data obtained using the finite-difference time-domain (FDTD) technique. Finally, we have designed and fabricated a dual-mode bandpass filter using this resonator.

A /spl lambda//2 CPW resonator BPF with multiple attenuation poles and its miniaturization

Very simple method for creating multiple attenuation poles of a bandpass filter (BPF) based on a /spl lambda//2 coplanar waveguide (CPW) resonator with tap-coupling is proposed, Moreover, miniaturization of the CPW-BPF using a stepped impedance resonator (SIR) is also carried out, As a consequence, the bandpass characteristics with multiple attenuation poles are obtained together with the reduced filter size. The derivation of multiple attenuation poles and a method for reduced filter size are also detailed,.

FREQUENCY CHARACTERISTICS OF THE MAGNETIC SPATIAL SOLITONS ON THE SURFACE OF AN ANTIFERROMAGNET

The frequency characteristics of magnetic spatial solitons on the surface of two-sublattice uniaxial antiferromagnetic crystal have been studied. The distinguishing feature of the solitons is the existence of the frequency passband(s) and stopband(s) that can be switched into each other by varying the power. This is because the nonlinear permeability is not only power dependent but also frequency dependent in infrared frequency region. The passband width may increase sharply with the power when the dielectric constant of the antiferromagnetic crystal is smaller than that of the nonmagnetic substrate. The passband may vary as much as 100 GHz below the infrared resonance frequency of the system.