Mitsuo Tateiba

Radar cross sections of conducting elliptic cylinders embedded in strong continuous random media

Abstract The radar cross section (RCS) of a conducting elliptic cylinder in a strong continuous random medium is analysed numerically for E-wave and H-wave incidences, by solving the wave scattering as a boundary value problem. The numerical analysis shows that the spatial coherence of an incident wave on the cylinder has an important effect on the RCS, besides the well known effect of double passage, and that the spatial coherence effect depends on the curvature of the elliptic surface illuminated by an incident wave and the size of the ellipse.

Strong backscattering enhancement for partially convex targets in random media

Abstract Earlier work pointed out that the radar cross section (RCS), owing to the double-passage effect on waves propagating through random media, is enhanced by a factor ranging from one up to three. However, our study has manifested numerically a strong enhancement in RCS of targets with concave-convex surfaces in continuous random media, by taking account of boundary conditions of waves on targets. We have found that when a plane wave illuminates a convex portion of the concave–convex conducting target in a random medium, the factor of enhancement oscillates about two with target size. Moreover, this enhancement becomes quite large at certain target shapes and also under a specific condition of target size and spatial coherence length of the incident H-wave. The large enhancement is considered as an anomalous feature in the behaviour of backscattered waves in random media. By analysing the scattering problem for beam-wave incidence on the same target in free space, we manifest the mechanism of such anomalous enhancement.

Backscattering enhancement for partially convex targets of large sizes in continuous random media for E-wave incidence

Abstract The shape of the target constitutes an important factor in the radar detection problem. In a previous study, the enhancement in the radar cross section (ERCS) has proved to be affected largely by the target parameters as well as the effects of the double passage and the spatial coherence length of incident waves around the target. However, the target size was limited to about less than one wavelength. Here, we estimate numerically the RCS of targets taking large sizes of more than three wavelengths, and analyse the characteristics of RCS. Moreover, we investigate the ERCS phenomenon of such targets under different circumstances of random medium and target configuration. In this regard, we assume partially convex targets in continuous random media and also horizontal incident wave polarization (E-wave incidence).

A comparative study of the effective dielectric constant of a medium containing randomly distributed dielectric spheres embedded in a homogeneous background medium

Abstract The effective dielectric constant ∈eff of a medium containing randomly distributed dielectric particles has been analysed by conventional methods: Foldys approximation, the quasi-crystalline approximation (QCA) and the QCA with coherent potential. These conventional methods, however, have been indicated to become invalid for particles with a high dielectric constant; we have thus presented a new method that is valid for them. This paper compares ∈eff of our method with those of the conventional methods by changing the volume fraction and the dielectric constant of spheres. As a result, our method is shown to be more powerful for the analysis of ∈eff than the conventional methods.

The effect of H-polarization on backscattering enhancement for partially convex targets of large sizes in continuous random media

Abstract In our previous work, we have proved that the spatial coherence length (SCL) of the incident waves around the target together with the target configuration play a leading role in the determination of the enhancement in the radar cross-section (ERCS) of a target in a random medium. Owing to the double-passage effect, the ERCS is almost two when the SCL is much smaller or larger than the target size. However, for a SCL comparable with the target size, the ERCS deviates from two, depending on the target parameters and the SCL. The last conclusion was proved only for E-polarization. The polarization of incident waves is one of the key parameters in scattering problems. In this work, we extend our study and investigate the effect of H-polarization on the radar cross-section and the ERCS for large-size targets.

An indirect estimate of RCS of conducting target in random medium

This paper discusses an indirect estimate of the radar cross section (RCS) of a conducting cylinder with a partially convex cross-section under the condition that backscattering enhancement occurs in a random medium. Once we evaluate the spatial coherence length (SCL) of the incident waves around the cylinder in the random medium, we may estimate the RCS approximately from the RCS in free space with beam wave incidence in which the spot size equals the SCL. This method is restricted only to the case where the SCL is larger than the target size.

Mechanism of spot dancing

The mechanism of spot dancing is clarified by the application of wave theory in a random medium. The solution is based on the moment equation which prescribes the statistical properties of waves scattered successively in the forward direction. Spot dancing is described by the use of wave function; the relation between the spot dancing and the random medium becomes clear. Spot dancing is a limited phenomenon in wave motions. The distribution of arrival position is normal along the two-dimensional Cartesian coordinates, and the variance is uniquely determined by the correlation function of the medium and the propagation length of the wave. In addition, the Rice-Nakagami distribution of irradiance can be physically interpreted as the log-irradiance distribution in the spot dancing of a Gaussian wave beam.

Measurement of Ku-band rain attenuation using several VSATs in Kyushu Island, Japan

Rain attenuation at three different locations about 100 km from each other within Kyushu Island, Japan, are simultaneously measured in the Ku-band by utilizing JCSAT-1B communication satellite and several very small aperture terminals (VSATs). Two points are highlighted. The first one is the relation between rain attenuation and rain intensity. The relation is shown at uplink, downlink, and total link paths and is compared with the estimated International Telecommunication Union Radio Communication Sector (ITU-R). The second one is the rain attenuation distribution for a small percentage of time for a year for the total link path. These experimental results suggest the necessitity of detailed study on rain attenuation at local points and of presentation of a method for predicting bit errors, when using effectively Ka-band satellite systems with multispot beams.

The Lorentz reciprocity in random media—The derivation from Maxwell's equations

The Lorentz reciprocity in random media is mathematically derived from Maxwells equations on the assumption that the media are isotropic and that the material parameters e and μ are uniformly bounded random functions and exist in a finite region. It should be emphasized that the assumption is sufficiently satisfied in physics and that other conditions for e and μ are not assumed. The Lorentz reciprocity is valid in the sense that the reciprocal relation holds for any order moment of electromagnetic fields. The result and the derivation process presented here are useful for analyzing the wave propagation and scattering in random media.

Infinite-Series Expressions of Current Generators in Wave Scattering from a Conducting Body

In order to analyze wave scattering from a conducting body surrounded by random media, we defined current generators as an operator that transforms incident waves into surface currents on the body. Current generators are usually expressed in terms of the inverse matrix of which each element is the inner product of basis functions called sometimes modal functions. If the body is a cylinder with circular or elliptic cross-section, the basis functions can be chosen to be orthogonal ones and the inverse matrix becomes diagonal one; consequently, current generators are expressed in infinite series. This paper deals with the infinite-series expressions of current generators for circular and elliptic cylinders by using cylindrical or Mathieu functions according as the circular or elliptic cross-section of cylinders. These explicit expressions are useful for the analysis of scattering problems.