Keisuke Konno

Optimization of Block Size for CBFM in MoM

The optimum number of blocks of the CBFM is derived theoretically and demonstrated numerically. The minimum order of CPU time for the CBFM is shown to be O(N7/3) , where N is the number of unknowns. In addition, the optimum size of overlapping region of the blocks also is investigated numerically.

Improvement in the light outcoupling efficiency of organic light-emitting diodes using a hemispherical lens and a multipatterned one-dimensional photonic crystal fabricated by autocloning

The outcoupling efficiency of organic light-emitting diodes was improved using a photonic crystal fabricated by autocloning, which has potential advantages for mass production. By using layer thicknesses optimized by optical simulations, the experimental external quantum efficiency of a device with the photonic crystal and a hemispherical lens was 43.4%, which is 2.13 times that of a device on a flat substrate without the lens. Comparisons with the simulated distributions of the light modes in the devices show that the photonic crystal reduces the light loss from the waveguide and evanescent modes. The emission pattern was independent of substrate rotation.

Design of Compact Multiband Antenna for Triple-Band Cellular Base Stations

In this letter, a tapered-slot antenna (TSA) that covers 1.5/2/2.4-GHz bands is designed for a 6-sector base station. It is shown that the TSA with desired half-power beamwidth and front-to-back (F/B) ratio at the frequency bands can be designed by loading the two pairs of slits and reflector. Results of numerical simulation show that the designed TSA radiates a sector beam with high F/B ratios over 20 dB at 1.5/2/2.4-GHz bands.

Fast Computation of Layered Media Green's Function via Recursive Taylor Expansion

The layered media Greens function (LMGF) is useful as a kernel of the method of moments (MoM) for a thin stratified medium. The self/mutual impedance expression of the MoM in conjunction with the LMGF includes a semi-infinite spectral integral inside the multiple integrals over spatial variables. As a result, computation of impedance matrix entries is quite costly. In this letter, an interpolation method by using the Taylor expansion is proposed. The method precomputes the spectral integral for a single spatial variable. The derivatives in the expansion are found in closed form using the recursive property of the Bessel functions. After that, the precomputed results of the spectral integral are interpolated via the Taylor expansion when the multiple integrals over spatial variables are performed. Due to the proposed method, the spectral integral and multiple integrals over spatial variables are separated from each other, and the resultant CPU time becomes quite manageable for very large problems.

Wideband Scattering Performance of Reflectarray Using Log-Periodic Dipole Array

In this letter, wideband scattering performance of a reflectarray composed of a log-periodic dipole array (LPDA) is designed and studied numerically and experimentally. The reflectarray is designed using method of moments. Numerical simulation demonstrates that a reflectarray composed of the LPDA is wideband because the LPDA works as a wideband reflectarray element due to its self-complementary structure. The reflectarray is fabricated using a three-dimensional printing technology, and its scattering performance is experimentally confirmed. Finally, it is shown that the 1-dB and 3-dB bandwidths of the designed reflectarray are 45% and 64%, respectively.

Scattering Performance of Log-Periodic Dipole Array

In this letter, the scattering performance of a log-periodic dipole array (LPDA) is numerically and experimentally demonstrated. Radiation and scattering performance of the LPDA is shown. Numerical simulations clarify that a 3-dB bandwidth of an LPDA scatterer becomes narrow due to the distortion of its RCS pattern. Relation between the total length and bandwidth performance of the LPDA scatterer is numerically examined to extend its narrow bandwidth. The optimized LPDA scatterer achieves the bandwidth of 1:1.8. The optimized LPDA scatterer is fabricated, and the measured scattering performance is shown to confirm the numerical results.

Analysis of linear antenna near dielectric object by CBFM

Dipole antenna in the vicinity of dielectric object is analyzed by characteristic basis function method (CBFM). Accuracy of numerical analysis is investigated by using different block division for the antenna and dielectric object. It is shown that all antenna segments should be allocated in the same block for calculating input reactance accurately. In addition, it is demonstrated that polarization current in the vicinity of the dipole antenna must be allocated in the block including antenna segments.

Numerical analysis of finite periodic array antenna using novel characteristic basis function method

This paper deals with a novel characteristic basis function method (CBFM) for numerical analysis of a finite periodic array antenna. The CBFM uses uniformity of current distribution of the periodic array to reduce its computational cost. Results of numerical simulation show that the computational cost of the CBFM is O(N) where N is the total number of unknowns.

Reflectarray design by induced electromotive force method

A design method of reflectarray by the induced electromotive force method is proposed. The effect of oblique incidence from a primary source to a reflectarray element is included in the design process of the reflectarray by the proposed method. The CPU time for design of the reflectarray by the proposed method is small because mutual coupling between reflectarray elements are ignored. The reflectarray which consists of a dipole and parasitic dipole element is designed by the proposed method and the performance of the proposed method is shown.

Efficiency improvement with a recursive Taylor expansion of Bessel functions for layered media Green's function

This paper demonstrates the performance of a novel interpolation technique for computing the impedance matrix with a layered media Greens function (LMGF). The interpolation technique is based on a recursive Taylor expansion of a Bessel function of arbitrary order. Numerical simulation of microstrip array antennas embedded in a multi-layer medium is performed and the performance of the interpolation technique is demonstrated.