Nobuaki Kumagai

Finite-Element Analysis of Waveguide Modes: A Novel Approach that Eliminates Spurious Modes

An efficient finite-element method for analyzing the propagation characteristics of a wide variety of waveguides is presented. A variational expression suited for the finite-element method is formulated in terms of the transverse electric and magnetic field components. In this approach all guided-mode solutions are real, while the spurious-mode solutions are not real. Therefore, discrimination of the spurious-mode solutions can be achieved merely by imposing the simple condition that guided-mode solutions be real. Three numerical examples, two for the isotropic case and the other for the magnetic anisotropic case, are carried out.

Experimental studies of magnetically scannable leaky-wave antennas having a corrugated ferrite slab/dielectric layer structure

The radiation characteristics of a magnetically scannable leaky-wave antenna using a corrugated ferrite slab supported by a Teflon waveguide have been demonstrated experimentally. A corrugated polycrystalline yttrium iron garnet (YIG) slab having the dimensions 150.0 mm*15.0 mm*10 mm has been fabricated. The corrugation depth, corrugation spacing, and number of corrugations are 150.0 mu m, 2.0 mm, and 55.0, respectively. Experiments have been carried out in the millimeter-wave frequency range from 40.0 to 50.0 GHz. The main beam direction of the leaky wave shifts continuously about 41.0 degrees at the operating frequency 46.8 GHz by altering the DC magnetic field up to 1.4 T. It is found that the corresponding half-power beamwidth varies from 3.2 degrees to 3.6 degrees and a maximum scanning rate is 1.0 degrees /0.02 T. Experimental results are compared with theory based on the dispersion relation of the ferrite slab/dielectric layer structure. >

Analysis of the guided modes in slab-coupled waveguides using a variational method

The waveguiding properties of the slab-coupled waveguides (i.e., the optical stripline and the rib waveguide) are investigated by the vector variational method. The slab-coupled waveguides are low-loss optical waveguides which are easy to fabricate and design. In this paper, the propagation constants and the field intensity distributions of the slab-coupled waveguides are presented, and the effects on the wave-guiding properties caused by changing their geometrical parameters are discussed. The results obtained by employing the variational method are compared with those obtained by using other methods.

Reflection and Transmission of Electromagnetic Waves by a Dielectric Half‐Space Moving Perpendicular to the Plane of Incidence

The present paper describes reflection and transmission of a plane electromagnetic wave by a dielectric half‐space which is moving uniformly perpendicular to the plane of incidence. It is found that for the incident E plane wave both the reflected and transmitted waves are no longer an E plane wave but a linear combination of E and H plane waves. In addition, it is shown that for the incident E wave the E‐wave components of the reflected and transmitted waves carry a positive power, but the power flow with regard to the H‐wave component of the transmitted wave is always negative while the power carried by the H‐wave component of the reflected wave is always positive.

Scattering of Guided Modes Caused by an Arbitrarily Shaped Broken End in a Dielectric Slab Waveguide (Correction)

Electromagnetic scattering of guided modes in a dielectric slab waveguide caused by an arbitrarily shaped broken end is analyzed theoretically by using the integral equation method. By solving the integral equations iteratively, the tangential components of the electric and magnetic fields on the broken end surface are determined, from which the reflected mode power, the radiation wave power and field patterns, and the total scattered power are obtained. Numerical results are presented for the plane-perpendicular, plane-tilted, and arc-shaped end surfaces. Both TE and TM modes are assumed as an incident wave.

Truncated Parabolic-Index Fiber with Minimum Mode Dispersion

The use of a parabolic-index fiber as an optical transmission line has been receiving extensive attention because of its excellent mode dispersion characteristics. In the present paper, the modal dispersion in the optical fiber with truncated parabolic index distribution is analyzed theoretically in detail by using a variational method. Taking the influence of the cladding upon the propagating modes into consideration, it is found that there exists an optimum index distribution for which the modal dispersion is minimized. The standard deviation of the normalized group delay of propagating modes is used to estimate the modal dispersion behavior of the fiber.

The magnetostatic surface‐wave propagation in a corrugated YIG slab

An analysis for the propagation characteristics of the magnetostatic surface waves in a YIG slab having periodically corrugated surfaces is presented. The Brillouin diagrams, close to the intersection point (ω,β) of m=0 and m=−1 space harmonics, are obtained for different strengths of modulation. Comparison between the magnetostatic surface waves and volume waves concerning the complex value of the propagation constant within the stop band is also discussed.

Extended integral equation formulation for scattering problems from a cylindrical scatterer

An extended integral equation is developed for electromagnetic scattering from a perfectly conducting cylinder and a dielectric cylinder. The conventional surface integral equations cannot yield unique solutions when the wavenumber of the electromagnetic wave is equal to an eigenwavenumber of the system. Several methods to overcome this difficulty have been presented, but each method includes some drawbacks. A numerical method is proposed in which the boundary element method is applied to the extended integral equations with the observation points lying on a closed surface inside the scatterer. It is shown that the extended integral equations have unique solutions for any given wavenumber. As examples, plane wave scattering from a perfectly conducting elliptic cylinder, a dielectric elliptic cylinder, and a dielectric rectangular cylinder is numerically analyzed. >

Bragg Interaction of Electromagnetic Waves in a Ferrite Slab Periodically Loaded with Metal Strips

The waveguiding characteristics of electromagnetic TE waves in a ferrite slab periodically loaded with metal strips are investigated. Theoretical formulation by means of the spectral domain approach is employed to obtain the Brillouin diagrams of two types of volume modes and a surface mode. It is found that the nonreciprocal properties of waves depend on the metal strip profile and bias magnetic field strength. Experiments on the magnetic-field dependence of the Bragg frequency and the stop bandwidth are carried out in the millimeter-wave frequencies. Typical results obtained from a polycrystalline YIG slab with periodic gold strips deposited on one surface are stop bandwidth about 2.14 GHz, with return loss about 2 dB at the Bragg frequency of 47.5 GHz, for the bias magnetic-field strength of 5.7 kG. The Bragg frequency can be tuned over the range of 1.39 GHz by varying the bias magnetic field from 0 to 8.2 kG. Experimental results show good agreement with theoretical predictions.

Analysis of wave modes in slab waveguide with truncated parabolic index

The exact wave equation for a lenslike dielectric medium derived from Maxwells equations contains the term of gradient of permittivity e. The purpose of this correspondence is to clarify the effect of the \bigtriangledown \epsilon term on the propagation constants of the modes. We find that the propagation constants of the lower order modes suffer significant modification by taking the \bigtriangledown \epsilon term into account, while for the higher order modes the effects are small enough to be disregarded.