The nonlinear study of microstrip lines containing ferrite dielectric layers

In this paper, the transient responses of microstrip containing ferrite dielectric layers are studied by using extended FD-TD method. When the microwave signal propagating along the microstrip is comparable with the applied DC magnetic field on the ferrite, the nonlinearity of ferrite medium is represented. The propagating procedure of Gaussian pulse in the microstrip are simulated. It is shown that the effects of the pulse amplitude on the transmission distortion of Gaussian pulse is pronounced.     

Antenna patterns of nonsinusoidal waves with the time variation ofa Gaussian pulse

The development of antenna theory for nonsinusoidal electromagnetic waves has been based on the idealized rectangular pulse. In practice, an antenna that is designed to operate in the mode of an electric hertzian dipole would radiate a pulse that best approximates a Gaussian one when the driving current consists of a linear transient. The principle of radiation of nonsinusoidal electromagnetic waves with the time variation of Gaussian pulses is discussed. The properties of the Gaussian pulse are presented, i.e., the autocorrelation function, energy spectral density, and spectrum. Antenna patterns, such as peak-amplitude pattern, peak-power pattern, energy pattern, and slope pattern are derived for a Gaussian pulse received (or radiated) by a linear array antenna. Computer plots of the derived antenna patterns are presented that show a considerable improvement in the angular resolution capability over that of the antenna patterns that have been derived for a rectangular pulse     

FDTD中微带线激励源设置的新方法

ＦＤＴＤ已广泛应用于微带问题的计算中,本文提出了一种新的微带线馈电激励设置方式,同以往的激励设置方法不同,它不仅能计算Ｇａｕｓｓｉａｎ脉冲激励也能计算正弦波激励,计算过程中,源平面无需切换成吸收边界,场区的划分使反射场自然从总场区分离出来。     

Radiation From a Vertical Electric Dipole in the Presence of a Three-Layered Region

We study in detail both the lateral wave and trapped surface wave generated by a vertical electric dipole over the air-dielectric boundary on a wide range medium such as sea and lake water and wet and dry earth. Graphs of the far-field pattern are shown and compared with the available results. Especially, when both the dipole point and the observation point are on the surface of dielectric-coated earth, the trapped surface wave is dominant.     

Rayonnement d’une antenne microruban de forme arbitraire

This paper gives a rigorous approach to the problem of the radiation of microstrip antennas by using the surface electric currents circulating on the upper conductor of the antenna (patch). The model used in this study is a stratified medium in which the substrate and the ground plane both have infinite transverse dimensions. Asymptotical expressions for the far field of a Hertz dipole, located on the surface of the substrate, are obtained with a complex integration technique in the spectral plane. The radiated fields result from the superposition of a spherical space wave and a cylindrical surface wave. The relative amplitude of both waves and their behaviour in terms of substrate parameters and frequency are discussed in some detail. Finally, the theory of antenna arrays was utilized to evaluate the radiation of a microstrip antenna of arbitrary shape.     

Radio wave propagation along mixed paths through a four-layeredmodel of rain forest: an analytic approach

This paper presents a novel full-wave analysis of the radio waves that are excited from a dipole antenna located in the trunk layer and propagate inside a four-layered forest medium. The dyadic Green's functions for the four-layered geometry are applied first to derive the integral expression of the electric fields. The closed form of the electric fields is then obtained by using the quasi-static approximation, saddle-point technique, and branch-cut integrations in the complex plane and, hence, expressed in terms of direct waves, multiple reflected waves, and lateral waves. Two kinds of images, i.e., the quasi-dynamic and complex images, are considered in the integration in the complex plane. Among those waves excited by a dipole antenna in the four-layered medium, it is shown theoretically and numerically that the lateral wave along the upper-side air-canopy interface plays a role of dominant modes. The propagation mechanism of other lateral waves due to the air-canopy, canopy-trunk, and trunk-ground interfaces is also discussed and analyzed so as to gain an insight into the wave characteristics. Transmission losses of the lateral waves are calculated numerically     

面向RFID应用的几种2.45 GHz微带天线的分析比较

随着RFID的广泛应用,微带天线已经成为RFID中不可缺少的一部分,常见的微带天线有单偶极子和双偶极子天线。根据目前RFID的应用,提出了几种基于2.45 GHz的板载天线,同时结合天线的基本理论对这几种结构进行了分析,并通过HFSS软件进行仿真比较。通过对仿真结果的分析,讨论了各种微带天线的优缺点,为RFID的应用提供了参考。     

基于偏振调制器的可变超宽带脉冲产生

In order to generate optical Ultra- Wideband (UWB) pulse train with a switchable shape, a novel method based on a Polarization Modulator (PolM), a Polarization Controller (PC) and a delay line, is proposed and exp-erimentally demonstrated. Experimental resu-lts show that when a Gaussian pulse is applied to the PolM, under different phase shifts introduced by the PC, a gauss or gauss doublet pulse will be generated at the output of the Polarization Beam Splitter (PBS). If the two- path signals after PBS are properly de-layed, Gaussian monocycles or third-order gauss pulses will be generated at the output of the Polarization Beam Combiner (PBC).     

A full-wave model for EMI prediction in planar microstrip circuitsexcited in the near-field of a short electric dipole

A full-wave model to evaluate the interference induced in planar microstrip lines of arbitrary shape exposed to the near-field of an elementary electric dipole is presented. The analysis of the line response, consisting in the evaluation of the surface current excited along the microstrip line, is based on the electric dyadic Green's function method. The surface current induced on the metal strip which, for the sake of generality, is considered as embedded in the dielectric substrate, is obtained solving by means of the spectral-domain approach (SDA) the electric integral equation, which enforces the boundary condition of zero tangential electric field on the surface of the strip. The induced current is computed for different line geometries and loads, and for various positions (inside or outside the dielectric substrate) and orientations of the dipolar source. Indications towards reducing the level of the signal induced on the loads of the line are inferred     

Calculations of the dispersive characteristics of microstrips bythe time-domain finite difference method

A direct time-domain finite-difference method is used to recharacterize the microstrip. Maxwell's equations are discretized both in time and space and a Gaussian pulse is used to excite the microstrip. The frequency-domain data are obtained from the Fourier transform of the calculated time-domain field values. Since this method is completely independent of all the above-mentioned investigations, the results can be considered as an impartial verification of the published results. The comparison of the time-domain results and those from the frequency-domain methods has shown the integrity of the time-domain computations. This method is very general and can be applied to model many other microwave components     

基于Matlab微带线静电场分析

推导出二维Laplace方程的有限差分公式,用Matlab语言编写程序,实例分析并绘制了屏蔽单微带线、屏蔽耦合微带线的等位线和电场强度分布图。实例计算结果表明:Matlab在解决实际的工程和数学问题中,具有使用更为简便、语句功能更强的特点,能直观地演示屏蔽微带线的电势分布图和场强立体分布图。     

A new absorbing boundary condition structure for waveguide analysis

The existence of evanescent waves and waves near cutoff frequencies limits the accuracy of the fields computed in waveguides using the finite-difference time-domain method, and prompted several researchers to design complicated boundary conditions, including combinations of perfectly matched layers and Higdon's higher order absorbing boundary conditions (ABCs). Instead, we employ a terminating structure in which the lateral walls are made absorbing in addition to the longitudinal walls. The undesirable lateral waves at the normal boundary interface are slowed down and effectively attenuated in the lateral walls, while the propagating waves are absorbed in the longitudinal walls. Numerical calculations for pulse excitation of a rectangular waveguide, using the simple Mur's first-order ABC, demonstrate the usefulness of the method     

A new approach to microstrip antennas using a mixed analysis:transient-frequency

An approach to microstrip antennas is developed that is based on a mixed transient-frequency analysis. The solution of transient integral equations by the method of moments allows one to compute the transient currents on the antenna. The Fourier transform of these transient currents used in asymptotic expressions for the far field of a Hertz dipole leads directly to harmonic parameters of radiation. The relative importance of spherical space waves and cylindrical surface waves and their behavior in terms of substrate parameters and frequency are discussed for some cases     

Antenna patterns of nonsinusoidal waves with the time variation ofa Gaussian pulse. IV

For pt.III see ibid., vol.31, no.1, p.34-47 (1989). An experimental setup of a large-current radiator and a closed-loop sensor has recently been developed for the radiation and reception of nonsinusoidal electromagnetic waves. The time variation of the radiated waves approximately equals that of a Gaussian pulse. Here, oscillograms of antenna current and radiated nonsinusoidal pulses are presented. Magnetic flux lines representing the radiation of Gaussian pulses from a large-current sheet radiator of physical dimensions w×d×s are plotted in analogy to the plots first derived by Hertz in the late 1800s for the radiation of sinusoidal waves by a Hertzian dipole. The flux lines form closed contours as they radiate from the surface of the radiator to the far zone. The density of the flux lines at any distance from the radiator is proportion to the magnitude of the produced field strength     

Substrate Optimization for Integrated Circuit Antennas

The reciprocity theorem and integral equation techniques are employed to determine the properties of integrated-circuit antennas. The effect of surface waves is considered for dipole and slot elements on substrates. The radiation and bandwidth of microstrip dipoles are optimized in terms of substrate thickness and permittivity.     

Approximate formulas for lateral electromagnetic pulses from a horizontal electric dipole on the surface of one-dimensionally anisotropic medium

In this paper, approximate formulas are derived for the electromagnetic pulse due to a delta-function current in a horizontal electric dipole on the planar boundary between a homogeneous isotropic medium and one-dimensionally anisotropic medium. The components of the electric field consist of two delta-function lateral pulses which decrease with the amplitude factor /spl rho//sup -2/ and travel along the boundary with different velocities and different amplitudes. Also, it is noted that the formulas for the time-dependent magnetic field components obtained by Fourier transforms from the approximate formulas in the frequency domain are not adequate.     

Coupling Between Guided Surface Waves, Lateral Waves, and the Radiation Fields by Rough Surfaces--Full-Wave Solutions

In this paper explicit expressions are presented for the guided surface waves and lateral waves that are excited when radiation fields are incident upon rough surfaces. Similarly, expressions are presented for the radiation fields scattered by rough surfaces that are excited by surface waves and lateral waves. In addition, coupling between the surface waves and the lateral waves due to surface irregularities is considered in detail. The solutions, which are based on a full-wave approach to the problem, are subject to the exact boundary conditions at the irregular interface. These are shown to be consistent with the reciprocity relationship in electromagnetic theory. The validity of the approximate impedance boundary condition is examined and consideration is given to excitation at the grazing incidence, the Brewster angle, and to waves incident at the critical angle for total internal reflection. Optimum conditions are determined for coupling between the radiation fields, the surface waves, and the Iateral waves incident upon irregular boundaries. Thus this work is applicable to problems of radio wave propagation near an irregular interface between two media and excitation of guided waves by irregular dielectric structures.     

Transient fields of a horizontal electric dipole on a multilayereddielectric medium

The transient electric fields of a horizontal electric dipole excited by a short pulse current and located on a layered dielectric medium were analyzed using the Cagniard-de-Hoop method. The fields are expressed as the convolution of the exciting current with the layered medium response. The layered medium response is obtained directly from the integral representation for the electric fields in the frequency domain and is expressed as a finite integral. In contrast to the conventional frequency synthesis approach, the Cagniard-de-Hoop (1960) method proves to be computationally more efficient and numerically more stable. Compared with the asymptotic approach, the solution involves no approximation. The nature of the various waves, reflected waves (guided wave and leaky wave), and lateral waves can be easily recognized on the Cagniard integral path. Numerical results are obtained to provide a rigorous forward modeling for the geo-radar operating on layered media