Impedance-type boundary conditions for a periodic interface betweena dielectric and a highly conducting medium

Using the homogenization method, we derive a generalized impedance-type equivalent boundary condition for the electromagnetic (EM) field at a two-dimensional (2-D) periodic highly conducting rough surface with small-scale roughness. The results obtained in this paper generalize ones obtained preciously for the case of a perfectly conducting rough surface. We will show that the coefficients in this equivalent boundary condition can be interpreted in terms of electric and magnetic polarizability densities. We also show that when the roughness dimensions are small compared to a skin depth of the conducting region (a smooth interface), the generalized impedance boundary condition given here reduces to the standard Leontovich (1948, 1985) condition. Results for the reflection coefficient of a plane wave incident onto a 2-D conducting interface are presented. We show the importance of the boundary-layer fields (as used in this study) over that of classical methods when calculating the reflection coefficient from a highly conducting rough interface. This work will lead to an analysis of the effects of surface roughness on power loss in MIMIC circuits     

Along-Track Focusing of Airborne Radar Sounding Data From West Antarctica for Improving Basal Reflection Analysis and Layer Detection

This paper presents focused synthetic aperture radar (SAR) processing of airborne radar sounding data acquired with the High-Capability Radar Sounder system at 60 MHz. The motivation is to improve basal reflection analysis for water detection and to improve layer detection and tracking. The processing and reflection analyses are applied to data from Kamb Ice Stream, West Antarctica. The SAR processor correlates the radar data with reference echoes from subsurface point targets. The references are 1-D responses limited by the pulse nadir footprint or 2-D responses that include echo tails. Unfocused SAR and incoherent integration are included for comparison. Echoes are accurately preserved from along-track slopes up to about 0.5deg for unfocused SAR, 3deg for 1-D correlations, and 10deg for 2-D correlations. The noise/clutter levels increase from unfocused SAR to 1-D and 2-D correlations, but additional gain compensates at the basal interface. The basal echo signal-to-noise ratio improvement is typically about 5 dB, and up to 10 dB for 2-D correlations in rough regions. The increased noise degrades the clarity of internal layers in the 2-D correlations, but detection of layers with slopes greater than 3deg is improved. Reflection coefficients are computed for basal water detection, and the results are compared for the different processing methods. There is a significant increase in the detected water from unfocused SAR to 1-D correlations, indicating that substantial basal water exists on moderately sloped interfaces. Very little additional water is detected from the 2-D correlations. The results from incoherent integration are close to the focused SAR results, but the noise/clutter levels are much greater.     

Characterization of Reflective Defects in Fabry–Pérot Laser Diodes Through the Power Transmission Spectrum

Reflective defects in Fabry-Peacuterot (FP) laser diodes are characterized through the power transmission spectrum based on the Fourier transform method. From a single measurement, the defect reflection, transmission coefficients and the cosine value of the defect phase shift, are calculated through equations built on the intensities of the peaks associated with defects in the Fourier transformed transmission spectrum. Gain dispersion which is unavoidable in semiconductor laser diodes is taken into account in the calculations. Extensive numerical simulations are made which show that the calculated defect characteristics are not influenced by the defect length and position and better results are obtained as the round-trip gain of the FP laser is relatively low. The simulation also shows that the underestimation of the gain caused by insufficient resolution of the measurement system degrades the calculated parameters. A deconvolution process is accordingly introduced, which is able to greatly reduce the resolution influence. Amplified spontaneous emission from FP laser diodes with a single slot very close to the laser front facet are measured and used to characterize the slot. The slots act as reflective defects in the laser diode and are produced by etching a rectangular well into the laser waveguide. For two lasers on the same bar with nominally the same slot, good agreement in the calculated reflection coefficient and cosine value of the slot phase shift is obtained, but the slot transmission coefficients calculated are different, which is due to the round-trip gain difference observed in the two lasers under the same current injection     

Theoretical considerations in the optimization of surface waves on a planar structure

The problem of optimum excitation of surface waves on a grounded dielectric slab by means of slots in the ground plane is considered. By adopting a two-dimensional (2-D) model, analysis lead to closed forms for the power launched as surface waves and power leaked as radiation. Input admittance of a single slot source and mutual admittance between two slots are derived and utilized to design a three element Yagi array of slots to achieve a prescribed ratio of forward to backward surface wave power. As a development of the 2-D model, we allow finite extent of slot excitation by assuming a Gaussian E-field distribution across the slot. The effect of the Gaussian width on the excited surface wave power is studied. The analysis is relevant to the study of surface waves on printed circuits. Specifically, it applies to the implementation of power combiners based on quasioptical slab beam that have been recently introduced in the literature for use in the millimeter wave band.     

2-D periodic leaky-wave Antennas-part II: slot design

The far-field radiation patterns of a two-dimensional (2-D) periodic slot leaky-wave antenna (LWA) are studied. The antenna consists of a two-dimensional periodic array of slots in a conducting plane that is printed on top of a grounded dielectric slab. The antenna is excited by a simple source such as a dipole inside the slab. Reciprocity along with the spectral-domain method is used to calculate the far-field pattern, and the radiation characteristics of the structure are investigated. A comparison between the present periodic slot LWA and a 2-D periodic patch LWA discussed in Part I is given to show the advantages of the slot antenna for certain applications. The slot LWA can achieve high directivity patterns, and a circularly-polarized version of the antenna can achieve good circular-polarization at broadside.     

A Double Resonance Approach to Submillimeter/Terahertz Remote Sensing at Atmospheric Pressure

The remote sensing of gases in complex mixtures at atmospheric pressure is a challenging problem and much attention has been paid to it. The most fundamental difference between this application and highly successful astrophysical and upper atmospheric remote sensing is the line width associated with atmospheric pressure broadening, ~ 5 GHz in all spectral regions. In this paper, we discuss quantitatively a new approach that would use a short pulse infrared laser to modulate the submillimeter/terahertz (SMM/THz) spectral absorptions on the time scale of atmospheric relaxation. We show that such a scheme has three important attributes. 1) The time resolved pump makes it possible and efficient to separate signal from atmospheric and system clutter, thereby gaining as much as a factor of 10⁶ in sensitivity. 2) The 3-D information matrix (infrared pump laser frequency, SMM/THz probe frequency, and time resolved SMM/THz relaxation) can provide orders of magnitude greater specificity than a sensor that uses only one of these three dimensions. 3) The congested and relatively weak spectra associated with large molecules can actually be an asset because the usually deleterious effect of their overlapping spectra can be used to increase signal strength.     

具有谐波抑制功能的宽带圆极化宽缝天线

针对微波无线输能系统中接收天线质量轻、体积小、剖面低、易与微波电路集成的特点,设计了一款新型的具有谐波抑制功能的宽带圆极化宽缝接收天线。通过在长方形缝隙中添加末端具有圆形贴片的交叉结构实现圆极化性能,添加切角结构展宽圆极化带宽。在馈线上添加具有一定长度的开路支节,配合使用缺陷地结构共同实现谐波抑制功能。研究并测试了天线的反射系数、轴比、增益以及远场辐射方向图,仿真与实测基本吻合。仿真结果显示,该天线很好地抑制了基频5.8 GHz的二次谐波和三次谐波,在4.5~6.2 GHz的范围内S11<-10 dB,相对阻抗带宽31.8%;基频5.8 GHz处的轴比AR=1.3 dB,在频率范围4.2~6.15 GHz内轴比AR<3 dB,相对轴比带宽37.7%;基频5.8 GHz仿真增益6.7 dB。     

Estimating two-dimensional frequencies by matrix enhancement andmatrix pencil

A new method, called the matrix enhancement and matrix pencil (MEMP) method, is presented for estimating two-dimensional (2-D) frequencies. In the MEMP method, an enhanced matrix is constructed from the data samples, and then the matrix pencil approach is used to extract out the 2-D sinusoids from the principal eigenvectors of the enhanced matrix. The MEMP method yields the estimates of the 2-D frequencies efficiently, without solving the roots of a 2-D polynomial or searching in a 2-D space. It is shown that the MEMP method can be faster than a 2-D FFT method if the number of the 2-D sinusoids is much smaller than the data set. Simulation results are provided to show that the accuracy of the MEMP method can be very close to the Cramer-Rao lower bound     

强光束经非线性光学界面反射特性的数值研究

用计算机数值模拟方法对非线性光学界面反射特性的数值研究表明,有限宽度平面波光束的反射特性明显不同于高斯光束;前者较后者有较低的阈值光强来实现界面由全反射到部分透射状态的转变。     

多区域柱面分层介质中的电磁散射—电磁波测井分析

本文讨论了径向柱面分层介质中全波分析的解析模式和数值模式方法.前者适用于任意激励形式下的场分析;后者在轴对称激励时,通过引入反射矩阵和透射矩阵的概念,可求解二维完全非均匀介质中的场.基于数值模式匹配理论,编制了适用于电磁波测井的计算机分析程序.通过实例计算,获得了与二维有限元方法完全一致的结果。而计算时间仅后者的1％.     

Design of 45-degree Linearly Polarized Substrate Integrated Waveguide-fed Slot Array Antennas

This paper presents a method of designing substrate integrated waveguide-fed (SIW-fed) slot array antennas. The design theory is based on the circuit model of slot and via as well as the reflection canceling. To prove the feasibility of this method, a 10-element K-band SIW-fed 45-degree linearly polarized slot array antenna with uniform power distribution is designed. By full-wave simulation, the antenna has a good impedance bandwidth of 7.5% and uniform power distribution. Besides, a maximum gain of 15.3dBi is obtained in the broadside and the cross polarization is suppressed below -23.5dB in the boresight. This type of SIW-fed slot array antennas can be a good candidate for microwave and millimeter-wave applications, especially for auto-motive collision-avoidance radar systems.     

1维光子晶体中TM波的传输公式及其辨析

为了得到1维光子晶体中TM波的传输公式,采用传输矩阵的方法和电磁波的边界条件,推导出TM波在介质层中的特征矩阵及其反射系数和透射系数公式。结果表明,用TE波反射系数和透射系数公式做代换的方法不能得到正确的TM波的反射系数和透射系数公式;对推导出TM波的反射系数和透射系数公式进行了分析,由TM波的反射系数和透射系数公式得出的光强透射率和反射率满足能量守恒;并且推出的TM波反射系数公式不仅能够反映反射波与入射波的数量关系,且能够反映反射波与入射波的位相关系。这些结果对研究1维光子晶体中TM波的传输性质是有帮助的。     

A reflection cancelling slot set in a linearly polarized radialline slot antenna

A radial line slot antenna (RLSA) is a high-gain and high-efficiency planar antenna. A linearly polarized RLSA (LP-RLSA) is attractive for applications of various subscriber radio systems. However, the slot arrangement for linear polarization gives rise to serious reflection from slots, which disturbs the normal antenna operation. A new LP-RLSA slot design is presented where reflection canceling slots are added to the conventional ones; four slots form one slot set as a unit radiator of linear polarization. The experiments confirm the design: the antenna return-loss is improved from -2 to -10 dB. Antenna efficiencies of 48 and 54% are measured for 400 and 600-mmφ antennas, respectively. This is the first report of the normal operation of LP-RLSAs     

介质覆盖导电球上缝隙天线的辐射

给出了用位函数方法推导介质覆盖导电球上缝隙天线辐射场严格解的过程.基于球Hankel函数加法定理,将基本磁流源激励的场展开为以球心为原点的球面波的叠加.利用球矢量波函数的定义及性质,提取出场的径向分量,将初级场分解为相对于径向的TE波和TM波,避免了复杂的矢量微分运算.在此基础上依据散射叠加原理,构造出各区域中场的一般表示形式,其中待定系数直接由球面分层介质中波的反射和透射规律给出.作为实际应用的例子,给出了介质覆盖导电球上均匀环缝问题的计算结果,并对结果进行了分析.     

一种六边形缝隙宽带微波天线设计

提出了一种适用于工业、科学、医学(ISM)频段的六边形缝隙天线的设计方法,采用基于全波分析矩量法的电磁场仿真软件进行分析,结果表明,与传统的正方形缝隙天线相比,天线的阻抗带宽由30%增加到了48.5%(|S11|<-10 dB)。进行了天线S参数测量,对天线通带起始频率5.24 GHz、谐振频率5.8 GHz和截止频率8.59 GHz三处频点的方向图进行了测量,测量结果和仿真结果一致,为拓展微带贴片天线带宽提供了一种新颖的方法。     

Closed-form solutions for one-dimensional inhomogeneous anisotropicmedium in a special case. I. Direct scattering problem

An analytical formulation is presented for the direct scattering problem of one-dimensional (1-D) inhomogeneous anisotropic medium in a special case. This method gives nonlinear differential equations for the reflection coefficients of the anisotropic medium. Applying the discontinuity condition of the dielectric parameters at the interface of the medium with free space, approximate closed-form solutions for the reflection coefficients are obtained. Numerical examples show the validity of the method     

Two-dimensional photonic crystals in macroporous silicon: frommid-infrared (10 μm) to telecommunication wavelengths (1.3-1.5 μm)

We present a detailed study of two-dimensional (2D) photonic crystals based on macroporous silicon technology, showing a broad range of wavelengths accessible for applications with this material. In this work, we have reached 1.55 μm, this certainly represents a decisive issue for this technology. First, the reflection performances of a hexagonal and a triangular lattice of air holes are compared. The triangular lattice reduces technological requirements because the complete photonic bandgap (PBG) results from the overlap of broader forbidden bands of lower order. Second, a combined experimental and theoretical study is presented of the reflection properties of a 2D photonic crystal in a three-dimensional (3D) optical environment. This reveals the critical parameters that can degrade the performances of such 2-D structures. Reflection coefficients up to 98% are obtained with optical quality interfaces. Finally, a complete PBG centered at 1.55 μm is demonstrated with a submicrometer period triangular lattice defined by holographic lithography. The influence of the air filling factor on the band position and the interface quality is analyzed by reflection measurements. The overall results show the high flexibility of the macroporous silicon technology and its applicability to integrated optics at telecommunication wavelengths     

The reflection of electromagnetic waves from stratified anisotropicmedia

A direct approach to the investigation of the reflection of electromagnetic waves from a plane interface separating a vacuum half-space and a stratified anisotropic layer is presented. The formulation involves the generation of a Riccati differential equation for a certain 2×2 reflection matrix. The approach is already well established for scalar problems, but its implementation in cases which allow mode conversion is believed to be new. The reflection matrix concerned is unitary when the anisotropic layer is nondissipative, and an efficient numerical method to solve the equation is outlined. Sample results are presented to illustrate the theory     

Comparison of FDTD algorithms for subcellular modeling of slots inshielding enclosures

Subcellular modeling of thin slots in the finite-difference time-domain (FDTD) method is investigated. Two subcellular algorithms for modeling thin slots with the FDTD method are compared for application to shielding enclosures in electromagnetic compatibility (EMC). The stability of the algorithms is investigated, and comparisons between the two methods for slots in planes, and slots in loaded cavities are made. Results for scattering from a finite-length slot in an infinite plane employing one of the algorithms are shown to agree well with published experimental results, and power delivered to an enclosure with a slot agree well with results measured for this study     

Analysis of a wide radiating slot in the ground plane of amicrostrip line

An analysis of a wide rectangular radiating slot excited by a microstrip line is described. Coupled integral equations are formulated to find the electric current distribution on the feed line and the electric field in the aperture. The solution is based on the method of moments and using the space domain Sommerfeld-type Green's function. The information about the input impedance or reflection coefficient is extracted from the electric current distribution on the microstrip line utilizing the matrix pencil technique. The theoretical analysis is described and data are presented and compared with other theoretical and experimental results