Frequency Selective Characteristics of Dielectric Periodic Structures for Millimeter Wave Application

In this paper, the frequency selective reflection characteristics of dielectric periodic structures for the oblique incidence of a plane wave are analyzed by a method which combines the multimode network theory with the rigorous mode matching method. The variations of the total reflection characteristics with the geometric dimensions of the dielectric periodic structures are systematically investigated to develop useful guidelines for the design of the dielectric frequency selective surface. Moreover, the relationship between the related wave phenomenon and the dispersion characteristics of multilayer plane dielectric structure is explained with the theory of plane dielectric waveguide.     

介质周期结构频率选择特性的多模网络分析

本文采用多模网络与严格模匹配相结合的方法分析了平面波斜入射时介质周期结构的频率选择反射特性。讨论了这种结构全反射的频率、带宽和在确定频带内出现全反射的个数随周期层厚度、附加介质层厚度及介电常数的变化关系,为介质频率选择表面结构的设计提供了依据。最后用平板介质波导理论说明了这种波现象与多层平板介质结构导模色散特性的关系。     

Toward controllable photonic crystals for centimeter- andmillimeter-wave devices

In this paper, we present several experimental and theoretical studies showing the feasibility of active photonic crystal controlled either by electrical elements or by light. The controllability of photonic crystals at centimeter wavelengths is proposed with the periodic insertion of diodes along the wires of a two-dimensional (2-D) metallic structure. For only three crystal periods with commercially available devices, more than 30 dB variations of the crystal transmission are predicted over a multigigahertz range by switching the diodes. From calculation models, a tight analogy is shown between these crystals and those consisting of discontinuous metallic rods with dielectric inserts. The numerical models as well as the proposed technology are validated by experimental measurements on 2-D crystals with either continuous or discontinuous metallic rods. The partial control of a 3-D layer-by-layer dielectric structure at millimeter wavelengths is also demonstrated in the second part of the work. A laser light is used to modulate the transmission level of defect modes by photo-induced free carrier absorption. The overall results are expected to contribute to further developments of switchable electromagnetic windows as well as to tunable waveguide structures in the microwave and millimeter wave domains     

Radiation and scattering from infinite periodic printed antennaswith inhomogeneous media

The hybrid method of moments (MoM)/Green's function method technique is applied to infinite periodic printed antenna arrays containing dielectric inhomogeneities. The solution uses an integral equation for an infinite periodic printed array on or over a homogeneous dielectric substrate, coupled with equivalent volume polarization currents for dielectric inhomogeneities on top of the homogeneous substrate. Volume pulse-basis functions were used to expand the volume polarization currents. A hybrid MoM/Green's function method solution was then obtained through the matrix form of the problem. The two-dimensional (2-D) solution of plane wave scattering from a grounded dielectric slab was used to validate the reaction impedance of the dielectric inhomogeneity. Several infinite periodic printed dipole arrays with dielectric supports and overlays were studied with this solution and good agreement was observed between the hybrid MoM/Green's function method and waveguide simulator experiments     

Radiation characteristics of dielectric-coated coaxial waveguideperiodic slot with finite and zero thickness

The leaky wave radiated from the dielectric-coated coaxial waveguide periodic slot with finite and zero thickness is investigated theoretically for the infinite and finite periodic structures. For the infinite periodic structure, mode-matching technique and integral equation method are applied to the analysis of finite and zero thickness slot cases, respectively. The integral equations are derived for the finite periodic structure by use of the Fourier transform and mode expansion and simultaneous linear equations are obtained. The effects of the slot thickness, the finite slot number and the dielectric coating are analyzed. Results for finite periodic slots are compared with those of the infinite extent structure and good agreement is found     

An integral equation analysis of an infinite array of rectangulardielectric waveguides

An integral equation analysis is applied to the study of the propagation characteristics of an infinite array of dielectric waveguides. The geometry under study is assumed to be rectangular. To find the Green's function of the structure, the Floquet theorem is applied such that the mutual coupling between dielectric waveguide elements is effectively included in the analysis. The effect of the coupling on the propagation characteristics of a dielectric waveguide is studied by varying the size of the Floquet cell. The validity of this analysis to simulate the case of an open dielectric waveguide is confirmed by a comparison with previous results, this in spite of the fact that radiation and leaky wave modes are not accounted for. The complex modes due to the periodicity of the structure are found and their properties are described. The analysis presented, with minor modification, can deal with the problems of dielectric image lines, or dielectric-loaded metallic waveguides     

Scattering Analysis of Dielectric Periodic Structures by an Oblique Incidence

The scattering of dielectric periodic structures by a plane wave incident in the direction oblique to the periodic grooves is analyzed by a method which combines the multimode network theory with the rigorous mode matching method. Combining the TE and TM characteristic mode functions determined in the corresponding 2-D scattering problem resulting from a TE or TM wave incident along the principal-plane of the same structure, and using a simple mathematical transformation, the 3-D scattering problem by an oblique incidence is rigorously solved.     

LEAKY CHARACTERISTICS OF A NEW MILLIMETER WAVE ANTENNA BASED ON GROOVE GUIDE WITH AN ASYMMETRIC CONDUCTOR STRIP

A new millimeter wave leaky wave antenna is presented in this paper, which is a modification of the groove guide with an asymmetric conductor strip by introducing a dielectric slab into the conductor plane region of the groove guide antenna. The leakage property of the new antenna is carefully examined through calculations of an equivalent network, which is developed here with taking into account the coupling between different modes to guarantee the calculating accuracy. It has been found that the new leaky wave antenna is of larger leakage constant than that for the original groove guide antenna because of the introduction of the dielectric slab. Extensive numerical results of the leakage characteristics are given to establish useful guidelines for the design of the new type groove guide leaky wave antenna.     

Leaky NRD guide as a feeder for microwave planar antennas

Although leaky wave antennas have been studied extensively in the literature, their practical use is still limited. This work proposes a novel and unique application of leaky NRD guides as feeding systems for microwave planar antennas and shows their substantial possibilities of practical use. At first a new leaky waveguide is introduced based on a periodic array of grooves on the upper side of the dielectric strip in the NRD guide. Then, leaky waves issuing from this configuration are used to feed a slot array cut on the upper metal plate of the NRD guide. Design examples of linearly and circularly polarized planar antennas were constructed, and their characteristics were measured at 23 GHz. The obtained results show the validity for this application of the leaky waveguide     

Simple high frequency solution for interior fields of open-ended parallel plate waveguide

The problem of electromagnetic (EM) plane wave scattering by an open-ended, perfectly-conducting, semi-infinite two-dimensional (2-D) parallel plate waveguide with a thin uniform layer of lossy material on its inner walls is analysed using a high frequency method. The fields coupled into the waveguide from the exterior are found via the uniform geometrical theory of diffraction (UTD) ray method.<>     

Analysis of the characteristics of NRD waveguides loaded with periodic metallic strips by using the method of lines for millimeter wave filter and antenna application

In this paper, the propagation characteristics of NRD waveguide loaded with periodic metallic strips are analyzed in terms of the method of lines. Numerical results show that such structures are most suitable for millimeter wave bandstop filter and NRD waveguide beam scanning leaky wave antenna application.     

Scattering by a Cylindrical Post of Complex Permittivity in a Waveguide

An exact solution of the discontinuity problem of a circular cylindrical post of arbitrary complex permittivity centered in a rectangular waveguide with the axis parallel to the electric field vector of the dominant mode has been set up and numerical results based directly on this solution have been found rising an electronic computer. The method used divides the waveguide up into three different regions by introducing two imaginary plane walls perpendicular to the waveguide walls. In the center region, which contains the cylindrical rod, the electromagnetic field is expanded in cylindrical waves and in the outer regions the field is expanded in waveguide modes. By setting up the boundary conditions at all discontinuity surfaces and performing numerical matching of the fields at the two imaginary walls, a system of linear equatious determining the coefficients of reflection, transmission, and absorption of the field due to the cylindrical rod is found. The structure which is of most interest in the case of a plasma column is a coaxial structure consisting of an inner dielectric cylinder with complex permittivity (the plasma) surrounded by a dielectric sleeve with real, positive permittivity (the glass tube). The theory is therefore developed to apply generally for such structures. From the numerical results, curves have been obtained showing the relationship between the coefficients of reflection and transmission and the (complex) permittivity of the rod material. Such curves maybe used for deducing the microwave properties of a cylindrical rod from measurements of the reflection and transmission coefficient of the rod.     

Design of novel power splitters by directional coupling between photonic crystal waveguides

The design of a novel photonic crystal waveguide power splitter is presented. The proposed power splitter has three output ports, the coupling among three parallel photonic crystal waveguides can be considered as a multimode interference (MMI), and the positions of output waveguides are determined by those of twofold images which are formed by the self-imaging effect of multimode interference. The transmission characteristics of the splitter are investigated by using the finite-difference time domain (FDTD) and the plane wave expansion method. The output optical power in each port can be controlled by adjusting the radius of the dielectric rods in the coupling region, and the coupling effect among output ports is decreased by using the T-shaped output port. The results indicate that 1× 1, 1×2 and 1×3 type power splitters can be realized when the normalized radius of dielectric rods in the coupling region is 0.130, 0.180, 0.152 or 0.221, respectively.     

Full vectorial finite-element-based imaginary distance beampropagation solution of complex modes in optical waveguides

In this paper, we address accurate computation of complex propagation constants and field distributions of different modes, in general, lossless and lossy optical dielectric waveguides. Using the vector finite-element formulation of the beam propagation method combined with the imaginary distance propagation technique, sequence of both the guided and leaky modes can be accurately calculated. To show the versatility and numerical precision of the proposed technique, we compute the modes of three different three-dimensional (3-D) waveguide structures and compare the results against those of other, different, vector formulations. Further, we present the design of a higher order mode filtering device, based on a 3-D leaky mode optical waveguide     

Transmission Characteristics of Dielectric Tube Leaky Waveguide

Loss formula of the dielectric tube leaky waveguide is derived by using a transverse transmission-line model which carries most of the transmitted power in air inside a dielectric tube. It is shown that low-loss leaky waveguide can be realized in optical through submillimiter wavelengths with moderate guide parameters and the transmission loss does not depend strongly on the material losses. It is also shown that the attenuation constant of this leaky waveguide is smaller than that of the hollow waveguide by several orders of magnitude.     

Characteristics of guided and leaky waves on multilayer thin-filmstructures with planar material gratings

This paper presents the characteristics of guided (surface) waves and leaky waves on multilayer structures with planar implanted periodic dielectric blocks. A three-dimensional (3-D) integral-equation formulation in conjunction with the method of moments (MoM's) is used to find the propagation constants of the surface-wave and leaky-wave modes. The analysis deals with layered structures with irregular implants. Photonic band-gaps of both guided waves and leaky waves for rectangular air-implants are identified. Anisotropic properties of the surface waves and leaky waves are investigated. The design of leaky-wave antennas with the information of mode characteristics is discussed. The analysis is validated through the comparison with a low-frequency effective-medium approach and results for linear gratings     

Helix Leaky Waveguide

The propagation characteristics of leaky waves in a helix waveguide covered with a slitted cylinder are presented by a method of transverse network representation. The main interest is in helix waveguides with small pitch angles, characterized by a hybrid mode consisting of TE/sub 01/, and a small amount of TM/sub 01/ modes. The leaky wave discussed in this paper may then be regarded as a perturbation of the TM/sub 01/ wave by the slitted cylinder outside the helix. The radiation, metal, and dielectric losses are calculated numerically at a frequency of 50 GHz. The relation between the radiation loss and aperture angle of slit is very different from that of an ordinary leaky waveguide composed of a slitted cylinder without helix, especially when the distance between the helix and shield cylinder is about a quarter of the radial wavelength. The metal and dielectric losses are the same order as radiation loss, however the dielectric loss decreases as the power factor /spl epsiv/"/ /spl epsiv/' increases. The measured total attenuation constant averages about 5 dB/km, almost twice the theoretical value.     

Investigation of localized coupled-cavity modes in two-dimensionalphotonic bandgap structures

We present a detailed study of the localized coupled-cavity modes in 2-D dielectric photonic crystals. The transmission, phase, and delay time characteristics of the various coupled-cavity structures are measured and calculated. We observed the eigenmode splitting, waveguiding through the coupled cavities, splitting of electromagnetic waves in waveguide ports, and switching effect in such structures. The corresponding field patterns and the transmission spectra are obtained from the finite-difference-time-domain (FDTD) simulations. We also develop a theory based on the classical wave analog of the tight-binding (TB) approximation in solid state physics. Experimental results are in good agreement with the FDTD simulations and predictions of the TB approximation     

基于二维光子晶体的多频段太赫兹波滤波器研究

基于二维光子晶体,提出一种多频段 太赫兹(THz)波滤波器。在光子晶体中引入3条平行的横向波导,通过改变介质柱的半 径或插入半径较小的介质柱在 相邻波导之间构成耦合区域,使特定频率的THz波从中部波导耦合至上、下侧光子晶体波 导并分别从端口2和1输出, 其余的THz波经中部波导从端口3输出,最终达到多频段滤波的效果。利用时域有限差 分法和平面波展开法对所提出 的器件计算和仿真结果显示,频率为f=3.24和3.75THz的THz波分 别从端口1、2和3输出中,传输效率分 别达到95%和99% ,表明本文结构能很好实现多频段滤波效果。     

斜入射情况下介质周期结构三维散射问题的严格求解

本文采用多模网络与严格模匹配相结合的方法,以介质周期结构在平面波沿主平面二维斜入射情况下散射特性的分析为基础,经过巧妙的数学处理,严格求解了三维斜入射情况下介质周期结构的散射问题,从而为毫米波和光集成电路中有关介质周期结构的精确分析和奠定了基础.