Jay Kyoon Lee

WAVE PROPAGATION AND DISPERSION CHARACTERISTICS FOR A NONRECIPROCAL ELECTRICALLY GYROTROPIC MEDIUM

The general dispersion relation for a nonreciprocal electrically gyrotropic or a gyroelectric medium is derived in two distinct forms by using three different methods. One of them is a new method which can be used when the stratification of the layers is in the z-direction. The wave numbers corresponding to each dispersion relation are obtained in closed form. It is shown that there exist two types of waves, type I and type II, in a gyroelectric medium. The wave propagation is investigated and the polarization of the waves, resonances and cut off conditions are obtained for the principle waves. The general wave propagation regions are identified using resonances and cut off conditions. These regions are then used to construct the Clemmow-Mually-Allis (CMA) diagram. The conditions showing the frequency bands for which wave can propagate in each region are tabulated for the first time. The results presented in this paper can be used in the development of nonreciprocal devices and in ionospheric problems including radiation and scattering applications.

Dyadic Green's functions for an electrically gyrotropic medium

The complete set of dyadic Green’s functions (DGFs) for an electrically gyrotropic medium is obtained using a new formulation technique, which consists of a matrix method with dyadic decomposition in the k-domain. The analytic expressions for DGFs are represented in a unique form in terms of characteristic field vectors that exist in an electrically gyrotropic medium. It is shown that the dyadic decomposition greatly facilitates the calculation of an inverse operation, which is crucial in derivation of Green’s functions. The DGFs found here can be used to solve electromagnetic problems involving the ionosphere and new types of anisotropic materials such as ceramics and advanced composites.

The Complete Design of Microstrip Directional Couplers Using the Synthesis Technique

A symmetrical microstrip directional coupler design using the synthesis technique without prior knowledge of the physical geometry of the directional coupler is analytically given. The introduced design method requires only the information of the port impedances, the coupling level, and the operational frequency. The analytical results are first validated by using a planar electromagnetic simulation tool and then experimentally verified. The error between the experimental and analytical results is found to be within 3% for the worst case. The design charts that give all the physical dimensions, including the length of the directional coupler versus frequency and different coupling levels, are given for alumina, Teflon, RO4003, FR4, and RF-60, which are widely used in microwave applications. The complete design of symmetrical two-line microstrip directional couplers can be obtained for the first time using our results in this paper.

Far field radiation from an arbitrarily oriented Hertzian dipole in the presence of a layered anisotropic medium

Far field radiation from an arbitrarily oriented Hertzian dipole for two-layered uniaxially anisotropic medium with a tilted optic axis is treated analytically by using the dyadic Greens function of the problem when the dipole is placed over or embedded in a two-layered uniaxially anisotropic medium. The radiation fields are evaluated using the steepest descent method. Parameter studies including anisotropy, layer thickness and dipole location are performed to investigate the effects of changing different variables on the radiation fields. Results of this work can be applied in microstrip circuits and antennas.

Analysis of higher order regular polygonal loop antennas

Higher order regular polygonal loop antennas are analyzed. The input impedance of higher order antennas varies gradually when the operating frequency or the order of polygon changes. This behavior of input impedance provides a wide range of input impedance and many resonant points to antenna designers. The higher order regular polygonal loop antenna generally possesses higher directivity but poorer broadband impedance property. As the operating frequency becomes higher its directivity increases remarkably and the broadband property becomes more prominent. To achieve the desired properties one may select one of the many design data sets with a trade-off between broadband property and directivity. >

The Unified-FFT Algorithm for Fast Electromagnetic Analysis of Planar Integrated Circuits Printed on Layered Media Inside a Rectangular Enclosure

The unified fast Fourier transform (UFFT) methodology is proposed for fast method of moments analysis of dense integrated circuits embedded in layered media inside perfectly electric conducting or perfectly magnetic conducting enclosures of rectangular cross section. The pre-corrected fast Fourier transform (FFT) method is modified to handle the dyadic Greens function (DGF) of shielded layered media through factorization of the DGF into four convolution/correlation terms enabling fast matrix solve operations (MSOs). Calculation of the impedance matrix elements in the form of an infinite series of waveguide modes is cast into the form of a 2-D discrete Fourier transform allowing for fast FFT-accelerated matrix fill operations (MFOs). Fast FFT-enhanced MSOs and MFOs used in conjunction form the UFFT method. The computational complexity and memory requirements for the proposed UFFT solver scale as O(NlogN) and O(N), respectively, where N is the number of unknowns in the discrete approximation of the governing integral equation. New criteria specific to shielded circuits for the projection of the current expansion functions on a uniform FFT grid are developed. The accuracy and efficiency of the solver is demonstrated through its application to multiple examples of full-wave analysis of large planar circuits.

DYADIC GREEN'S FUNCTIONS FOR UNBOUNDED AND TWO-LAYERED GENERAL ANISOTROPIC MEDIA

The dyadic Greens functions (DGFs) for unbounded and layered general anisotropic media are considered in this paper. First, the DGF for unbounded problem is derived using the eigen- decomposition method. Two difierent approaches are proposed to obtain the DGF for layered problem when the source is located inside the anisotropic region. The flrst approach is to apply the modifled symmetrical property of DGF to obtain the DGF for the fleld in the isotropic region when the source is located inside the anisotropic region, from the DGF for the fleld in anisotropic region when the source is in the isotropic region. This modifled symmetrical property can be applied for the layered geometry with bounded anisotropic region being either reciprocal or non-reciprocal medium. However, this method can not give the DGF for the fleld inside the anisotropic region. Thus, the second approach is presented to obtain the complete set of DGFs for all the regions including the anisotropic region, by applying the direct construction method through eigen-decomposition together with matrix method.

SIMPLIFIED FORMULATION OF DYADIC GREEN'S FUNCTIONS AND THEIR DUALITY RELATIONS FOR GENERAL ANISOTROPIC MEDIA

A simplified method to obtain the complete set of the dyadic Greens functions (DGFs) for general anisotropic media is presented. The method is based on the k-domain representation of the fields in terms of wave matrices. The Fourier transformed Greens functions are calculated through the inverses of wave matrices. The inverses of the wave matrices, which lead to the final form of DGF, are obtained using dyadic decomposition technique. This facilitates the inverse operation significantly and gives DGFs clear vector representation, which helps their physical interpretation. The dyadic decomposition of the wave matrices has been presented for uniaxially anisotropic, biaxially anisotropic and gyrotropic media. The method of deriving DGF using the technique given in this paper is applied on a uniaxially anisotropic medium and verified with the existing results. It is shown that the knowledge of the inverse of one type of wave matrix is adequate to find the complete set of the dyadic Greens functions for a general anisotropic medium using the method presented. The duality relations of dyadic Greens functions are also developed. It is shown that once the dyadic Greens functions for one of the dual media are obtained, the DGFs for the other dual medium can be found by application of the duality relations shown in this paper.

REFLECTION AND TRANSMISSION FROM BIAXIALLY ANISOTROPIC | ISOTROPIC INTERFACES

In this paper we explore electromagnetic behavior of arbitrarily oriented biaxially anisotropic media; speciflcally with respect to re∞ection and transmission. The re∞ection and transmission of electromagnetic waves incident upon half-space and two-layer interfaces are investigated. The waves may be incident from either the isotropic region or the biaxial region. The biaxial medium considered may be aligned with a principal coordinate system or may be arbitrarily oriented. Critical angle and Brewster angle efiects are also analyzed.

Scattering from Three-Dimensional Dispersive Gyrotropic Bodies Using the TLM Method

A three-dimensional scattering fleld Transmission Line Modeling (TLM) algorithm is established to obtain bistatic radar cross sections of frequency dispersive gyromagnetic objects. Starting from the 1D TLM modeling of gyrotropic materials, a scattering fleld TLM algorithm is derived for 3D calculations. For veriflcation, the bistatic radar cross section results for several gyromagnetic structures are compared with the single frequency computations, where the permittivity and permeability tensors are made of complex constants at a given frequency.