Analysis of Antennas with PBG Substrate

The use of photonic materials has been used in the theory of optical waves. The PBG (Photonic Band Gap) theory and material, was developed recently for optical frequencies and can be easily applied to millimeter waves, microwaves and planar antenna frequencies. The presence of photonic materials as substrate in antennas has some good characteristics such as, supression of light spontaneous emission and suppression of surface waves, allowing the application in planar antenna array. In this work an elaborate analysis using the full wave Transverse Transmission Line - TTL method, that provides efficient and concise results is applied to the planar antennas array with PBG substrate.     

Microstrip Array with PBG Substrate

The phased array formed by microstrip antennas is analyzed using the full wave Transverse Transmission Line (TTL) method. For the microstrip patch resonator a set of equations that represents the electromagnetic fields in the x and z directions as function of the fields in the y direction are obtained applying the TTL method. The structure PBG (Photonic Band Gap) is analyzed using the homogenization theory, the objective is obtain the equivalent permittivity of structure. Numerical results of the radiation pattern for some phase excitation in a phased array are shown.     

High precision analysis of finlines on semiconductor substrate

In this study, the effect of the metallization thickness in finlines on semiconcuctor substrate is researched. The propagation parameters are computed to measure the inluence of the metallization. The theory and numerical results are presented to the propagation constant and characteristic impedance of the bilateral and unilateral finlines. The full wave analysis of the transverse transmission line — TTL method is used to determine the electromagnetic fields of the structure in Fourier transform domain — FTD. Applying the suitable boundary conditions, the moment method and expanding the fields in a set of suitable bases functions, a homogeneous matrix system is obtained and the propagation constant is computed. The characteristic impedance is obtained using the relation of the voltage in the slot and the transmitted power by the structure.Computational programs are developed to obtain numerical results to the propagation parameters composed by the propagation constant and characteristic impedance.This work received financial support by CAPES and CNPq.     

Photonic band structure in a two-dimensional hexagonal lattice of equilateral triangles

In this paper, the plane wave expansion method is used to calculate the photonic band structure (PBS) for the transverse electric (TE) polarization in a two-dimensional hexagonal lattice composed air holes with cross-sections in the shape of equilateral triangles embedded in a GaAs background. We consider that the dielectric constant of GaAs is dependent on both hydrostatic pressure and temperature. Further, an increase can be observed in the width of the photonic band gap (PBG) while the lengths of the sides of the equilateral triangles are increased. When the pressure increases in the presence of a constant temperature, the dielectric constant of GaAs decreases; further, the PBS exhibits a more noticeable shift toward regions of higher frequencies than that observed while the temperature is increased at a given pressure. We also observed that the PBG obtained by rotating the triangular holes by an angle θ increases when compared against the results obtained for the lattice of holes without performing any rotation. In addition, the results obtained using the supercell technique denote that the position and width of the PBG remain unchanged while removing a triangular hole from the structure, denoting the presence of a defective band within the PBG.     

Design and analysis of thermally tunable liquid crystal filled hybrid photonic crystal fiber coupler

We propose a novel tunable photonic crystal fiber (PCF) coupler scheme, that the light is coupled between a total internal reflection (TIR) guiding core and a photonic bandgap (PBG) guiding core. By introducing the thermo-optic responsive nematic liquid crystals (NLC) into the air holes around the PBG core, the hybrid PCF based coupler exhibits enhanced thermal tunability. The thermo-optical characteristics of the proposed coupler are numerically studied using finite element method (FEM) and beam propagation method (BPM). The proposed design can find promising applications in filtering and sensing devices.     

Attenuation and propagation in various finline structures

The theory and numerical results of the asymmetric single and coupled bilateral and unilateral finlines and arbitrary antipodal finline considering the attenuation of the substrate are presented. Results are given to the complex propagation constant. The full wave analysis of the Transverse Transmission Line — TTL method is used in the FTD. Applying the moment method the complex propagation constant, including the attenuation constant and the phase constant, are obtained. The effective dielectric constant, _eff,, and the characteristic impedance are also calculated. The results are compared with the references, and news results are presented for these parameters.     

A new type of millimeter wave-integrated directional couplers

In this paper a new type of millimeter wave integrated directional coupler is proposed. The coupling mechanism on the narrow wall of waveguide consists of a series of bilateral E-plane slots deposited on a dielectric substrate by photo-etching technique. The modified generalized transmission parameters considering the thickness effects of the strips and higher order mode interactions at the step discontinuities in the coupling region are used in optimizing program. The calculated performance of a 3-dB 12-slot directional coupler at Ka-band is given. A prototype Ka-band coupler has been tested. The measured results agree with the theoretical prediction satisfactorily.     

Switching of transmission resonances in a two-channels coupler: A Boundary Wall Method scattering study

In this work, we study the transmission characteristics of a two-channels coupler model system using the Boundary Wall Method (BWM) to determine the solution of the corresponding scattering problem of an incident plane wave. We show that the BWM provides detailed information regarding the transmission resonances. In particular, we focus on the case of single channel input aiming to explore the energy switching performance of the coupler. We show that the coupler geometry can be tailored to allow for the first transmission resonances to be predominantly transmitted on specific output channels, an important characteristic for the realization of logical operations.     

Nondestructive testing in human teeth using a leaky Lamb wave device

A Lamb wave interdigital transducer mounted on a layered substrate composed of two plates, a thin piezoelectric ceramic plate and an acrylic plate, operating at a liquid-solid boundary, is investigated for ultrasonic nondestructive testing of the layer thickness in human teeth. A higher-order mode having a phase velocity higher than the longitudinal wave velocity in the human teeth can be used for nondestructive testing. In the combination of the two layers, the fourth mode of leaky Lamb wave is most favorable for a frequency-controllable radiation angle of an ultrasound beam into a water layer as an acoustic coupler. In the configuration of an acoustic delay line, the layer-thickness measurement in vivo, evaluated from the time interval between two reflected ultrasound echoes, is successfully realized under a thin water layer as the acoustic coupler.     

基于分形特征和双层光子带隙结构的宽阻带低通滤波器

提出一种新颖的基于分形特征和双层光子带隙（PBG）结构的宽阻带低通滤波器. 该滤波器在接地板上刻蚀一阶Sierpinski carpet PBG结构，在顶层微带线与接地板之间增加一层具 有三阶Sierpinski gasket PBG结构的金属层，该金属层经过打通孔与接地板连通. 这种双 层PBG结构的低通滤波器，具有良好的宽阻带特性，且电路尺寸小、结构紧凑. 对比了单层 普通方孔PBG结构的低通滤波器、单层一阶Sierpinski carpet PBG结构的低通滤波器和双层 分形PBG结构低通滤波器的传 关键词： 低通滤波器 双层PBG结构 分形 宽阻带特性     

空气环型二维光子晶体完全带隙特性研究

采用平面波展开法, 系统研究了空气环型二维光子晶体的完全光子带隙随结构参数变化而改变的规律, 并将其与普通的空气孔型和介质柱型二维光子晶体的完全带隙进行了比较. 研究表明: 空气环型二维光子晶体不仅可以获得更宽的完全带隙, 而且, 当介质折射率较低时, 其可以获得普通空气孔型和介质柱型二维光子晶体在低折射率条件下所无法获得的完全带隙. 关键词： 空气环型二维光子晶体 完全带隙 平面波展开法     

Finite difference time domain analysis of a photonic crystal substrate patch antenna

Planar microstrip patch antennas can achieve a wide range of radiation patterns. However, due to surface-wave losses, they have low bandwidth, low gain, and a potential decrease in radiation efficiency. In order to minimize the surface-wave effects, a photonic-band gap (PBG) substrate is proposed. The PBG structure significantly diminishes the surface-wave modes and thus improves the gain and far-field radiation pattern and efficiency. In this paper, using FDTD, an accurate full-wave analysis of surface-wave propagation in a rectangular microstrip patch antenna with and without PBG is presented. Finally, the antenna fabricated and result of measurement was compared with numerical simulation.     

One dimensional photonic band gap material as an omnidirectional reflector

In this article, the reflection properties in one-dimensional dielectric-dielectric photonic band gap (PBG) structure have been studied. We have used SiO₂ as material of low refractive index and Te as a high refractive index material. Reflectivity of proposed PBG structure is plotted as a function of wavelength and angle of incidence and omni-directional PBGs are computed theoretically. To obtain reflectance, we used transfer matrix method for solving Maxwell’s equations for electromagnetic wave in PBG structures. For a large range of frequency, the PBG structure is found to exhibit omni-directional reflection which can be exploited in devices such as optical resonators, mirrors, etc.     

二维光子晶体线缺陷结构的光谱辐射特性

光子晶体的禁带特性是该新兴材料的最根本特征。本文运用平面波展开法(PWE)计算了一种正方晶格Si光子晶体材料的禁带特性,并基于该材料设计出一种红外波段的线缺陷光子晶体波导结构。运用时域有限差分法(FDTD)研究了线缺陷二维光子晶体波导宽度对通频带、电场强度及透射能量的影响,研究结果为二维光子晶体波导器件的开发和利用提供了理论支撑。     

光子晶体压力传感器的基本原理

通过研究一维光子晶体受压力后其光带隙性能的变化，提出了光子晶体压力传感器的原理.计算表明，压力的大小与禁带起始波长、截止波长和禁带宽之间呈简单的线性对应关系.这就提供了通过测量光带隙性能而感知外载荷或者通过施加载荷而调制光带隙性能的可能.由于光子晶体的结构周期和光波波长为一个数量级，也就有可能制造出一系列精巧的压力、温度传感器或者其他精密仪器. 关键词： 压力传感器 光子晶体 光带隙性能     

Theoretical study on photonic devices based on a commensurate two-pattern photonic crystal

In two-dimensional optical chip applications, the optical wave is classified to two modes according to its polarization: TE and TM. It is desirable to integrate multiple optical wave control devices for different polarizations onto the same plane at the scale of the wavelength. Here we demonstrate a periodic two-pattern photonic crystal with a large, complete photonic bandgap (PBG). It comes from the superposition of two substructures: one contributes the TM PBG and the other contributes the TE PBG. By purposely introducing defects into the substructures, photonic devices for different polarizations can be integrated to bend, split, and resonate TM/TE waves simultaneously on the same plane.     

W波段交错双栅返波振荡器高频系统

将矩形交错双栅结构作为慢波电路并提出与之配套的过渡结构和输出耦合器,设计了利用带状电子注工作在W波段的返波振荡器。提出的过渡结构和耦合器解决了该类直波导型器件的信号传输衰减大、反射强等难题。相对于传统圆形电子注器件,该器件得到了较大的功率提升。利用三维粒子模拟计算的方法,在电流12 mA时通过调节工作电压,在92~98 GHz频带内得到了数W的稳定平均功率输出,信号中心频率非常接近设计频率,且单色性好,谐波分量小。     

Metal mesh couplers using evanescent waves at millimeter and submillimeter wavelengths

In this paper we introduce a metal mesh evanescent wave coupler that makes use of evanescent wave coupling between a metal mesh and a dielectric plate, as a quasi-optical component for millimeter and submillimeter wavelengths. The transmission properties of this type of couplers have been investigated experimentally and theoretically for both capacitive and inductive metal meshes in the frequency range from 40 GHz to 60 GHz. The transmittance of a capacitive metal mesh evanescent wave coupler can be adjusted more than 70% by changing the spacing between the capacitive mesh and the silicon plate less than 0.15 mm at around 57 GHz.     

Theoretical predictions of photonic properties of nanoporous copolymer films as photonic band gap materials using FDTD

Block copolymers (BCPs), which self-organize into ordered 1-, 2- and 3-dimensional periodic equilibrium structures, can exhibit photonic band gaps (PBGs). In this paper, cylinder microdomain nanoporous films are proposed to be treated as a new kind of 2-dimensional BCP based photonic crystal. The minor component of the nanoporous films has been removed chemically with only pores left in order to enhance their dielectric constant contrast, which provides a new solution to achieve necessary PBG properties with BCPs. The finite-difference time-domain (FDTD) method is used to investigate band features of this kind of photonic crystal theoretically. It is noted that the complete band gaps for the H polarization are obtained, although for the E polarization only the incomplete gaps exist. In addition, the gap map of the PBG materials is presented and its characteristics are analyzed. PACS 42.70.Qs; 42.70.Jk; 42.25.Bs     

同轴对称型主耦合器的研制

 为更进一步提高注入器的性能,注入器使用的耦合器采用同轴对称耦合。给出了同轴对称耦合器的理论计算、具体设计以及实验情况。经过对模型耦合器多次微波传输测量调试以及对各个部位反射的细致分析,最后获得了较好的结果,证明了该耦合器的实用性和可行性。