Electromagnetic analysis of an antenna embedded in a compositeenvironment

This paper addresses the problem of an antenna embedded in a hole dug in the ground. The composite medium configuration consists of a half-space dielectric (representing the Earth-air interface) containing a cylindrical hole filled with a different dielectric medium. The wire antenna resides within this hole, on the axis. The solution strategy is based on decomposing the problem into simpler subproblems, which are treated sequentially. First we calculate a numerical dyadic Green's function for the composite medium by solving an integral equation formulated over a background consisting of the unperturbed dielectric half space (for which the Green's functions are known in a spectral integral form). This integral equation is solved via the fictitious currents method, which is a special case of the method of moments. We then solve the integral equation for the antenna currents using this numerical Green's function and determine the input impedance and radiation pattern     

Rigorous Analysis of Rectangular Dielectric Resonator Antenna With a Finite Ground Plane

A probe-fed rectangular dielectric resonator antenna (RDRA) placed on a finite ground plane is numerically investigated using method of moments (MoM). The whole structure of the antenna is exactly modeled in our simulation. The feed probe, coaxial cable and ground plane are modeled as surface electric currents, while the dielectric resonator (DR) and the internal dielectric of coaxial cable is modeled as volume polarization currents. Each of the objects is treated as a set of combined field integral equations. The associated couplings are then formulated with sets of integral equations. The coupled integral equations are solved using MoM in spatial domain. The effects of ground plane size, air gap between dielectric resonator and ground plane, probe length, and position on the radiation performance of the antenna including resonant frequency, input impedance, radiation patterns, and bandwidth are investigated. The results obtained for the antenna parameters based on the MoM investigation shows that there is a close agreement with those obtained by measurement. Moreover it is shown that the MoM results are more accurate than other simulation results using software package such as High Frequency Structure Simulator (HFSS).      

Numerical analysis of arbitrarily shaped probe-excited single-armprinted wire antennas

A general integral equation technique is described for analysis of an arbitrarily shaped single-arm printed wire antenna excited through a vertical probe. A unified current integral equation is formulated on the basis of dyadic Green's functions and the reciprocity theorem. The current distribution is obtained by using a parametric moment method in which parameter segments are adopted for the printed wire instead of the commonly employed wire length segments. The radiation field solution involving both the printed antenna and vertical probe is also presented. The validity of the formulation is verified by comparing the numerically obtained input impedance and radiation patterns for a linear antenna and a meander antenna with measured data. A circular open loop and an Archimedian spiral are investigated to illustrate the applicability of the present technique     

Circular polarised cylindrical dielectric resonator antenna

A circular polarised cylindrical dielectric resonator antenna excited using a simple microstrip feed line is reported. The experimental results of the resonant frequency, radiation pattern, boresight axial ratio, gain, unloaded Q-factor, impedance bandwidth and radiation efficiency are presented     

Scattering by superquadric dielectric-coated cylinders using higherorder impedance boundary conditions

A general method for deriving higher order impedance boundary conditions is described. It is based on solving an appropriate canonical problem exactly in the spectral domain. After approximating the spectral impedance terms as a ratio of polynomials in the transform variable, elementary properties of the Fourier transform are used to obtain the corresponding boundary condition in the spatial domain. The method is applicable to multilayer coatings with arbitrary constitutive relations. Higher-order boundary conditions which neglect the effects of curvature are derived for a dielectric coating using the method. The boundary condition equation and the magnetic field integral equation are solved simultaneously using the method of moments, yielding the bistatic and monostatic radar cross section for dielectric-coated superquadric cylinders. The method is also applicable to a combined field integral equation (CFIE) solution, which can be used to eliminate the internal resonance problem associated with either the electric field integral equation (EFIE) or magnetic field integral equation (MFIE)     

Analysis of dielectric-resonator antennas with emphasis onhemispherical structures

An overview is given for the development of dielectric-resonator antennas. A detailed analysis and study of the hemispherical structure, excited by a coaxial probe or a slot aperture, is then given, using the dyadic Green's functions pertaining to an electric-current source or a magnetic-current source, located in a dielectric sphere. The integral equation for a hemispherical dielectric-resonator antenna (DRA), excited by either a coaxial probe or a slot aperture, is obtained. The integral equation is solved using the method of moments. The antenna characteristics, such as input impedance, radiation patterns, directivity, and efficiency, are computed numerically, around the resonant frequency of the TE₁₁₁ mode (the HEM₁₁ mode for cylindrical coordinates). The computed input impedance is compared with numerical and experimental data available in the literature     

Numerical analysis of two-arm spiral antennas printed on afinite-size dielectric substrate

A two-arm spiral antenna (SA) printed on a dielectric substrate backed by a conducting plane is analyzed under the condition that the dielectric substrate has a finite side length of L. The analysis is performed using the finite-difference time-domain (FDTD) method. The computation space for the FDTD method is reduced to one-half of the full computation space by virtue of the antenna arm symmetry with respect to the feed point. The numerical evaluations for the radiation characteristics are briefly described, and the SA_∞ (the spiral antenna with a conducting plane of infinite extent) is analyzed. It is found that the input impedance remains constant with side length L⩾0.8 wavelength in this analysis model. It is also found that as L increases, the axial ratio improves with the gain remaining relatively constant (the gain variation is within 1 dB). The SA_finite (the spiral with a conducting plane having the same finite size as the dielectric substrate) is also analyzed. It is revealed that the effects of L on the axial ratio and gain are relatively large compared with those on the former SA_∞     

加载介质覆盖层的圆柱共形微带天线的全波分析

基于严格的全波方法分析计算了介质薄层覆盖下由探针激励的圆柱共形微带天线的输入阻抗和辐射方向图.首次详细地推导出了此结构下适于数值计算的微带帖片上的表面电流形式,并通过矩量法求解电场积分方程得到感应电流的分布.最终,通过数值结果揭示出了覆盖介质层对天线特性的影响并且与已发表文献及其他数值方法的结果进行对比,证明了方法的正确性.     

Scattering from a microstrip patch

A solution to the problem of plane wave scattering by a rectangular microstrip patch on a grounded dielectric substrate is presented. The model does not include the microstrip feed, and thus does not include the so-called "antenna mode" component of the scattering. The solution begins by formulating an electric field integral equation for the surface current density on the microstrip patch. The integral equation is solved using the method of moments. Computed data for the patch radar cross section (RCS) is found to be in close agreement with measurements over a broad frequency range. The microstrip RCS versus frequency consists of a number of large peaks which are identified as impedance or pattern factor resonance peaks.     

Ferrite‐based wideband circularly polarized microstrip antenna design

In this paper, a wideband, circularly polarized patch antenna is proposed that leverages the unidirectional resonant modes of a circular patch mounted on top of a grounded dielectric‐ferrite substrate. The proposed antenna is fed via the proximity coupling method and several parasitically coupled patches are placed on a dielectric superstrate to enhance the impedance bandwidth of the antenna. The resonant modes of the structure rotate only in the clockwise or counter clockwise directions. In the frequency range where the effective permeability of the ferrite layer is negative, the resonance frequencies of these modes differ significantly, which produces a large axial ratio (AR) bandwidth. For the proposed antenna, the numerical results show the 10 dB impedance bandwidth to be around 44% and the 3 dB axial ratio bandwidth to be higher than 64%.     

基于MOM的舰船通信天线的特性分析

以舰船通信天线为研究对象，应用网格模型分析法及矩量法（MOM）对其进行计算分析，给出了求解复杂天线问题的一般思路。基于Pocldington积分方程和Galerking法，采用分段正弦函数展开，计算得出此类天线的输入阻抗和辐射方向图，并与无限大导体平面上的天线进行了比较。计算结果反映出了船体对舰船天线本身的影响。     

Integral equation analysis of a sheet impedance coated window slotantenna

Presents an integral equation and method of moments analysis of a window slot antenna. The antenna is modeled by a sheet admittance coated rectangular aperture in an infinite ground plane. It is shown that the sheet admittance coated aperture is complementary to a sheet impedance plate, which permits the window slot antenna to be analyzed with existing computer programs. Numerical results are compared with measurements for input impedance and radiation efficiency     

Theory and experiment of circularly polarized dielectric resonator antenna with a parasitic patch

The use of a single parasitic patch for circular polarization (CP) excitation of the dielectric resonator antenna (DRA) is investigated. For demonstration, the technique is applied to the conformal-strip fed hemispherical DRA, excited at the fundamental TE/sub 111/ mode. Using the Green's function approach, the integral equations for the conformal-strip and parasitic-patch currents are formulated by matching the appropriate boundary conditions. The equations are then solved using the method of moments (MoM). In using the MoM, both the rigorous and simplified current expansions are used for the parasitic patch, and their results are compared with each other. In each case, the impedance integrals are evaluated by virtue of newly obtained recurrence formulas and direct analytical integration. Hence, the results can be calculated very efficiently without the need for any numerical integration, which greatly facilitates the numerical implementation. The input impedance, axial ratio, and radiation patterns of the CP DRA are calculated, and the results are in good agreement with measurements.     

The slot-coupled hemispherical dielectric resonator antenna with a parasitic patch: applications to the circularly polarized antenna and wide-band antenna

The aperture-coupled hemispherical dielectric resonator antenna (DRA) with a parasitic patch is studied rigorously. Using the Green's function approach, integral equations for the unknown patch and slot currents are formulated and solved using the method of moments. The theory is utilized to design a circularly polarized (CP) DRA and a wide-band linearly polarized (LP) DRA. In the former, the CP frequency and axial ratio (AR) can easily be controlled by the patch location and patch size, respectively, with the impedance matched by varying the slot length and microstrip stub length. It is important that the AR will not be affected when the input impedance is tuned, and the CP design is therefore greatly facilitated. For the wide-band LP antenna, a maximum bandwidth of 22% can be obtained, which is much wider than the previous bandwidth of 7.5% with no parasitic patches. Finally, the frequency-tuning characteristics of the proposed antenna are discussed. Since the parasitic patch can be applied to any DRAs, the method will find applications in practical DRA designs.     

探针馈电印刷线天线的矩量法分析——（Ⅰ）单臂天线

利用同轴内导体延和为探针对印刷天线进行直接馈电是一种易于实现的馈电方式。本文介绍了一种分析单臂探针馈电印刷线天线的数值方法,该方法是基于并矢格林函数和互易定量求解电流积分方程的矩量法,适合于分析任意形状印刷线天线,首先给出描述电流分布的积分方程及其矩量法求解公式,在解得电流分布基础上,应用驻相法计算远区辐射场,通过计算与实验比较,验证了分析方法和计算程序的正确性,最后对一圆极化开口印刷圆环天线进行分析计算,表明了方法的实用价值。     

The analysis of arbitrarily shaped aperture-coupled patch antennasvia a mixed-potential integral equation

A mixed-potential integral equation (MPIE) is formulated for the electric and magnetic currents on a multilayered aperture-coupled patch antenna. The integral equation is solved via the method of moments (MoM) using subsectional basis functions that allow the analysis of nonrectangular aperture and patch shapes. The input impedance and radiation efficiency of various aperture-coupled elements are calculated using the proposed technique and compared to measured results. The advantages and disadvantages of several aperture and patch configurations are discussed, and six methods of numerically de-embedding the element's input impedance are compared     

Analysis of cavity-backed aperture antennas with a dielectricoverlay

A full-wave analysis of cavity-backed aperture antennas with a dielectric overlay is presented. The theoretical approach uses a closed-form dyadic Green's function in the spectral domain. The aperture equivalent magnetic currents are obtained using the surface equivalence theorem and an integral equation is obtained by matching the fields across the aperture. The moment method applied in spectral domain analysis is employed to solve the integral equation for the equivalent magnetic currents with proper combination of subdomain or entire domain expansion functions. Numerical results include the aperture field distribution and antenna parameters such as input impedance, bandwidth, and efficiency. A set of measurements data is compared with results based on the theoretical work     

Electromagnetic scattering from composite objects using a mixtureof exact and impedance-boundary conditions

Different surface integral equations for characterizing the electromagnetic scattering from a surface impedance object partially coated with dielectric materials are presented. The impedance boundary condition (IBC) is applied on the impedance surface and the exact boundary condition is applied on the dielectric surface. The resulting integral equations are solved for bodies of revolution using the method of moments. The numerical results are compared with the exact solution for a sphere. Other geometries are considered, and their results are verified by comparing results of the numerical solutions which were obtained using different formulations. The internal resonance problem is examined. It is found that the combined field integral equation (CFIE) can be used at any frequency and with any surface impedance     

Scattering from a finite array of microstrip patches

A full-wave solution to the problem of plane wave scattering by a finite array of rectangular microstrip patches printed on a grounded dielectric slab is presented. The electric field integral equation is solved using the spectral-domain Green's function/moment method approach. Derivations for the elements of the impedance and voltage matrices are presented. An efficient massively parallel computer implementation of the moment method solution is described. Computed radar cross section (RCS) data for microstrip patch antenna arrays are presented as a function of incident signal frequency and angle of incidence     

Synthesis of printed quadrifilar helical antenna

A method to reduce the axial length of a printed quadrifilar helical antenna by optimisation algorithm while maintaining the different features (radiation coverage, axial ratio, impedance) is investigated. The synthesis is performed on the antenna pitch angle