Shogo Kozaki

Propagation of the electromagnetic pulse with Gaussian envelope in inhomogeneous ionized media

For the purpose of radio communication, it is important to study the distortion of signals propagating through an inhomogeneous medium. The problem of finding the distortion of a pulse after it has propagated through a plasma medium whose electron density varies linearly in one direction is discussed. A sinusoidal carrier with a Gaussian pulse envelope is assumed to be the source of the incident plane wave.

Electromagnetic scattering by the Luneberg lens with reflecting cap

The near-field distribution in the case of the normal incidence to the Luneberg lens reflector is numerically obtained by using the modal expansion technique and point-matching method. As a model of the Luneberg lens, six different homogeneous media is used. A microwave experiment was also performed.

Scattering of Gaussian beam from a hemispherical boss on a conducting plane

A new expression of a Gaussian beam derived by using a spectral domain method is applied to the scattering problem from a hemispherical boss on a conducting plane. On the method of images, the original problem is reduced to that of the scattering of two Gaussian beams by a full sphere. The scattered fields are expressed in simple closed forms which are valid when the diameter of the boss is comparable to or less than the Gaussian beamwidth. The difference between the bistatic radar cross section of a Gaussian beam and that of a plane wave is discussed.

Propagation of electromagnetic pulse having a Gaussian envelope in longitudinally inhomogeneous anisotropic ionized media

For radio-wave communication with ionospheric propagation, it is useful to study the distortion of signals propagating through a plasma medium. The problem is discussed of finding the distortion of a pulse after it has propagated through a longitudinally inhomogeneous anisotropic ionized medium whose electron density varies linearly in one direction. As a model of the incident pulse source, the Gaussian envelope carrier pulse is considered. Dependence of the electromagnetic pulse distortion upon the duration of the pulse, the gradient of the electron density, the magnetostatic field, and the carrier frequency is mathematically studied in detail.

Reflection and transmission of radio waves at a medium with tapered conductivity

Expressions for the reflection and transmission coefficients are derived for the case where the plane wave is incident on a conducting medium in which the conductivity varies linearly with distance. Such a medium may be considered to be a model of wave absorbers. Approximate representations of the coefficients are obtained in simple form expressed by the elementary functions. Numerical evaluation of the solutions is made and results discussed.

Scattering of a Gaussian beam by a dielectric rectangular cylinder

For purpose of finding the dielectric constant, a new expression of the beam scattering is obtained by using the boundary element method (BEM) with extended boundary conditions. Comparison between with and without the resonant condition was made for the total scattered power. To find the accuracy, convergence property of the total scattered power versus divided number has been examined. To check the boundary conditions at the corner of the scatter, the electric field difference between inner and outer side has also been calculated and confirmed. The total electric field distributions in space are illustrated for the plane and beam wave. Microwave experiments was also performed.

A hybrid technique combining FDTD and series solution for near-to-far-field transformation

A new near-to-far-field transformation that combines the FDTD and the series solution is presented. In this method, near-field data is calculated by FDTD and far-field data is also expressed by series solution. The boundary condition is applied to a virtual surface, which encloses arbitrarily shaped scatterers. In order to verify this method, scattering patterns from this transformation are compared with scattering patterns from exact solution. Numerical results show that errors in the far-field data from this method is less than surface equivalence theorem. Thus, this method is valid for obtaining the far-field data.

Technique for calculation of the propagation constant in an optical planar waveguide with a Gaussian profile

We performed analysis of a planar waveguide with arbitrary index variations. We obtained numerical results for the propagation coefficient by using first-order Langer and Liouville transformations. The accuracy of the numerical results is confirmed by a comparison with those obtained by other methods.

T-matrix analysis of electromagnetic wave differaction from a Fourier grating

This paper is described for T-matrix analysis of the electromagnetic wave diffraction from a Fourier grating that the boundary value problem is treated by applying the extended boundary condition. The rigorous form of the expression of matrix elements is presented in the term of Bessel functions of the first kind. The error of power conservation versus the truncated number has been examined for mode number. Diffraction efficiencies versus groove depth and wavelength for a second or third harmonic wave of Fourier grating have been discussed. Numerical results are in good agreement with those obtained from other method and experimental values. Reasonable numerical results are presented for a groove depth per period of the Fourier grating less than 0.25.

Analysis of Spatial Transfer Function by Using FDTD for Wireless Communication

Spatial transfer function for wide band wireless communication system is analyzed by using FDTD and DFT method. Ray-based method is not sufficiently accurate, when the size of objects on the propagating path is comparable to the wavelength. In our proposed method, the tranfser function can be obtained exactly by using the FDTD method. For the numerical examples, the transfer functions in an aperture of the waveguide are calculated by proposed procedure. Furthermore, experimental verification is made by using two-dimensional propagation system, which is constructed of copper plates, antennas and vector network analyzer. The proposed algorithm is valid for estimating of the spatial transfer function.