Hisanao Ogura

Step-frequency radar

The step‐frequency radar is proposed as a means of detecting targets imbedded in high loss media. The radar derives information on target distance by exploiting the phase and amplitude characteristics of the returned signal. With a given frequency change, the phase angle change from a faroff target is larger, and therefore its phasor rotates faster, than that from a closeby target. Distance information is conveniently derived by applying the Fast Fourier Transform algorithm. The radar is able to offset an arbitrary distance and zoom to the targets, thereby obtaining fine resolution. With Wiener filtering, the resolution of the radar is high enough to identify the type, as well as the orientation, of the buried targets. A subtraction feature has also been incorporated which allows scattering from unwanted targets to be cancelled out from that of the wanted targets. The radar was successfully demonstrated for the detection and identification of various targets buried in sand, moist clay soils, underwater, a...

A hologram matrix radar

The concept of hologram matrix is proposed. This concept was incorporated into the design of a novel radar which, unlike conventional radars, determines the distance by the spatial distribution of the scattered wave rather than by the lapse of time. The radar based upon this principle was developed and built for the purpose of mapping ice thickness in the range of 0.5 ∼ 5 m, but it has potential applications in other fields. Such a radar has real-time processing capability, resulting from an amalgamation of the antenna and computer subsytems. The programability of the radiation pattern by software of the processing simplifies the construction of the radar. Capability of dual focussig of the transmitter and receiver eliminates the necessity of either pulsing, or frequency modulation of the transmitting signal. Superior performance in the short range, with high resolution, is particularly advantageous for measuring lossy ice. These features were substantiated by experimental results obtained from the field operation of the system.

Theory of light scattering from a random metal surface: Excitation of surface plasmons in a Ag film

The scattering of light by a silver film with a random rough surface and the excitation of surface plasmon modes at the metal surface are theoretically studied in detail by means of the new stochastic treatment. The silver film is assumed sandwiched between the air and a crystal and a plane wave is incident through the crystal to excite the surface‐plasmon mode. The stochastic formulation is developed for the stated problem and approximate solutions are obtained for the coherent and incoherent scattered waves involving the optical theorem. Details of the scattering characteristics are numerically calculated for various combinations of film thickness, surface roughness, and correlation length. The angular pattern of incoherent scattering into the crystal is shown to have two sharp resonant peaks due to the excitation of the surface plasmon, which are directly observable by an experiment.

Scattering of waves from a random cylindrical surface

Abstract The stochastic theory combined with a group-theoretic consideration developed by the authors for the scattering from a planar and a spherical random surface is applied to the case of a cylindrical random surface, which is assumed to be a homogeneous Gaussian random field, homogeneous with respect to the group of motions on the cylinder, translations along the axis and rotations around the axis. An operator acting on a random field is introduced, which keeps a homogeneous random field invariant, and which gives a representation of the motion-group on the cylinder. As an irreducible representation, i.e., an eigenfunction of the operator, the random wave field is obtained for the mth cylindrical wave injection on the random rough cylinder, and is represented as a stochastic functional of the cylindrical random surface in terms of a Wiener-Ito expansion. The random wave field for a plane-wave injection is decomposed into a sum over m of such random wave fields for the mth cylindrical wave injection. Various statistical characteristics of the scattered wave are calculated from the stochastic wave field so obtained; such as coherent scattering amplitude, coherent power flow, incoherent power flow, angular distributions for the coherent and incoherent scattering, and the power conservation law, especially, a stochastic version of the optical theorem stating that the total scattering cross-section consisting of the coherent and incoherent power flow equals the imaginary part of the coherent forward-scattering amplitude. Approximate solutions are obtained for a slightly rough cylindrical surface with Dirichlet and Neumann boundary conditions. Anomalous scattering does not take place in the case of a cylindrical Neumann surface, contrary to the case of a planar random surface, so that a single scattering approximation could be used for every small roughness. Some numerical calculations are shown of the angular distributions for coherent and incoherent scattering.

Green function and radiation over a random rough surface

A stochastic representation of the Green function, i.e., the radiation field from a point source above a homogeneous Gaussian random surface, is obtained as a stochastic nonlinear functional of the random surface, which is constructed by integrating the random wave field for a plane-wave incidence given in previous papers [ Radio Sci.15, 1049 ( 1980);Radio Sci.17, 558 ( 1982)]. Any mode of radiation can therefore be treated using the stochastic Green function. The stochastic analog of the optical theorem is established. The asymptotic expression of the Green function is evaluated by the saddle-point method, and statistical properties and radiation patterns of the coherent and the incoherent field are calculated.

Scattering of an electromagnetic wave from a slightly random cylindrical surface : horizontal polarization

Abstract The scattering of an electromagnetic wave from a random cylindrical surface ir studied for a plane-wave incidence with S-(TE) polarization, by means ofthe stochastic scattering theory developed by Nakayama, Ogura. Sakati et al. The theory is based on the Wiener-Ito stochastic functional calculus combined with the group-theoretic consideration concerning the homogeneity of the random surface. The random surface is assumed to be a homogeneous Gaussian random field on the cylinder C, homogeneous with respect to the group of motiolrs on C: translations along the axis and rotations around the axis. An operator D operating on a random field on C is introduced in such a way that D keeps the homogeneous random surface invariant This gives a reprerentation of the cylbdrical group and commutes with the boundary condition and the Maxwell equation. Thus, for an injection of the mth cylindrical TE or TM wave, which is a vector eigenfunction of the D operator, the scattered random wave field is an eigenfunctio...