Cavity-Backed Aperture Antennas with Dielectric and Magnetic Overlay

A method is presented for a full wave analysis of an aperture antenna backed by a rectangular cavity. The antenna may be covered by one or more dielectric and magnetic layers. The aperture antenna may be arbitrarily shaped but must be small compared to the cross section of the cavity. The analysis includes ohmic, dielectric, and magnetic losses in the cavity as well as in the overlay. Deriving a modified magnetic field integral equation, the treatment of the cavity and of the layered overlay is separated. A dyadic Green's function describing the topology of the cavity is formulated in the space domain. Another dyadic Green's function for the layered overlay is derived in the spectral domain. Subsequently, the integral equation is solved by the method of moments. The theoretical treatment is worked out for arbitrarily shaped apertures. Finally, the proposed method is applied to narrow slot antennas backed by rectangular cavities. Some numerical results are compared with experimental data     

A generalized method for analyzing shielded thin microstripdiscontinuities

An integral equation method for the accurate full-wave analysis of shielded thin microstrip discontinuities is described. The integral equation is derived by applying the reciprocity theorem and then solved by the method of moments. In this derivation, a coaxial aperture is modeled with an equivalent magnetic current and is used as the excitation mechanism for generating the microstrip currents. Computational aspects of the method have been explored extensively. A summary of some of the more interesting conclusions is included     

Full-wave boundary integral equation method for suspended planartransmission lines with pedestals and finite metallizationthickness

A boundary integral equation method is proposed for the full-wave analysis of suspended planar transmission lines with pedestals and/or finite metallization thickness. Coupled boundary integral equations are formulated on equivalent magnetic currents only on the apertures of subregions using the Green's identity of the second kind. Because it is possible to take a large number of terms in the series expansion of Green's functions in each subregion independently from the order of resulting matrices, this approach can avoid the relative convergence problem. Numerical results for suspended coplanar waveguides are found to have a stable convergence property and to be in excellent agreement with other available theoretical results. Numerical data reveal the effects of conductor thickness and aperture width on the transmission properties of suspended planar transmission lines with pedestals     

Electromagnetic transmission through mesh covered apertures and arrays of apertures in a conducting screen

The problem of electromagnetic transmission through wire mesh covered arbitrarily shaped aperture or arrays of apertures (possibly covered by a thin lossy dielectric sheet) in a perfectly conducting ground plane is considered. The equivalence principle and image theory are used to derive an integral equation for the equivalent magnetic currents. The method of moments is utilized to solve the integral equation, with the aperture modeled by triangular patches. Numerical results are presented for transmission coefficients and transmission cross-section patterns for electrically small apertures.     

A Nonmodal Formulation for Electromagnetic Transmission through a Filled Slot of Arbitrary Cross Section in a Thick Conducting Screen

This paper considers the two-dimensional problem of electromagnetic transmission through a filled slot of arbitrary cross section in a thick perfectly conducting screen. The equivalence principle is used to divide the original problem into three isolated parts where postulated equivalent sources radiate into unbounded, homogeneous media. These equivalent electric and magnetic currents are chosen to ensure continuity of the tangential components of electric and magnetic fields at each aperture. An integral equation is written for each of the three parts with the equivalent currents as unknowns. The resulting set of coupled integral equations is solved by the method of moments. It is shown in the Appendix that this set of equations has a unique solution. The primary quantities computed are the equivalent magnetic and electric currents on each aperture and the electric current on the remaining portions of the slot cross section. These results are compared with those obtained from a modal solution, where the fields in the slot cross section are expressed in terms of parallel-plate waveguide modes.     

Single integral equation for electromagnetic scattering bythree-dimensional homogeneous dielectric objects

A single integral equation formulation for electromagnetic scattering by three-dimensional (3-D) homogeneous dielectric objects is developed. In this formulation, a single effective electric current on the surface S of a dielectric object is used to generate the scattered fields in the interior region. The equivalent electric and magnetic currents for the exterior region are obtained by enforcing the continuity of the tangential fields across S. A single integral equation for the effective electric current is obtained by enforcing the vanishing of the total field due to the exterior equivalent currents inside S. The single integral equation is solved by the method of moments. Numerical results for a dielectric sphere obtained with this method are in good agreement with the exact results. Furthermore, the convergence speed of the iterative solution of the matrix equation in this formulation is significantly greater than that of the coupled integral equations formulation     

Aperture Excitation of a Wire in a Rectangular Cavity

The problem of determining the currents excited on a wire enclosed within a rectangular cavity is considered. The wire and cavity interior are excited by electromagnetic sources exterior to the cavity which couple to the cavity interior through a small aperture in the cavity wall. It is assumed that the wire is thin, straight, and oriented perpendicular to one of the cavity walls. An integral equation is formulated for the problem in the frequency domain using equivalent dipole moments to approximate the effects of the aperture. This integral equation is then solved numerically by the method of moments. The dyadic Green's function for this problem are difficult to compute numerically; consequently, extensive numerical analysis is necessary to render the solution tractable. SampIe numerical results are presented for representative configurations of cavity, wire, and aperture.     

Characteristic modes of a rectangular aperture in a perfectlyconducting plane

The objective of the paper is the analysis of a rectangular aperture in a perfectly conducting plane using the characteristic mode theory. The problem is first formulated as an operator equation involving the continuity of the tangential components of the magnetic field in the aperture region. The operator equation is used, with the help of the moment method, to determine the eigenvalues, eigencurrents, and the characteristic magnetic currents of the aperture. When these modes are determined, the equivalent magnetic current and other parameters of interest can then be obtained     

Radiation of printed antennas with a coplanar waveguide feed

This paper presents an analysis of conductor-backed aperture antennas with multilayered substrate. These printed antennas are fed by a coplanar waveguide (CPW). The theoretical approach taken is to develop an integral equation over the aperture region and apply Galerkin's procedure in the spectral domain. The properties of printed antennas with a CPW feed are characterized. Numerical results include the scattering parameters, antenna pattern, and radiation efficiency. The reflection coefficient, input impedance, and far-field pattern are also compared with measurements and good agreement is observed     

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 a cylindrical antenna containing an aperture coupledload

In this paper we present the basis for the analysis of shielded tuning networks coupled to wire antenna elements. The structure analyzed comprises three conducting cylindrical tubes that form an aperture-fed circular coaxial waveguide. Two methods are presented for formulating and solving integral equations for the structure. The first method is based on the mixed potential electric field integral equation enforced on the three cylindrical tubes, and the second is based on aperture theory. An end correction capacitance is used to adjust the reflection coefficient in the eigenmode expressions of the aperture method. The data obtained by the two methods are in close agreement. Differences in actual currents and equivalent currents obtained from solutions are discussed and reconciled     

一维FSS电磁散射宽带特性的快速计算

基于渐近波形估计（AWE）技术和矩量法（MOM），快速分析了一维频率选择表面（FSS）的宽带电磁散射特性，首先采用MOM法将平面波照射下FSS的电场积分方程（EFIE）转化为关于感应电流的矩阵方程，并由该方程确定频率导数矩阵方程（MEFD）；再在所考虑的频带内的某一给定频率处求解MEFD，得到给定频率处的频率导数感应电流；最后根据Pade逼近理论由给定频率处的频率导数感应电流确定周期性结构在任意频率入射波照射下的感应电流，根据FSS上的感应电流及谱域Floquet谐波模计算FSS的电磁散射宽带特性，计算结果表明，AWE能有效逼近MOM逐点扫描计算的结果，同时在计算速度上可加快十几倍。     

全等效电流积分方程法分析微带天线

提出了一种分析微带天线的新方法——全等效电流积分方程法。根据等效原理，用等效表面电流表示金属导体影响，用等效体极化电流来取代介质结构影响，建立全等效电流积分方程，结合空域矩量法来求解整个微带结构的电流分布。采用该方法可以分析任意结构的微带天线，只需用最简单的自由空间格林函数而无须求解复杂的谱域或空域格林函数，避免了无穷积分或Sommerfeld积分，且在分析中精确考虑了有限尺寸金属接地板的影响。用该方法分析了矩形微带天线，计算结果与其它文献给出的结果一致，证实了该方法的有效性。     

Scattering from narrow rectangular filled grooves

The solution of the integral equation for a small width rectangular groove is considered. It is shown that by retaining the dominant mode supported by the rectangular groove, the resulting quasi-static integral equations are comparable to those associated with the perfectly conducting narrow strip. They are, therefore, amenable to analytic solution yielding the exact field distribution or equivalent currents across the groove's aperture. The derived currents exhibit the same edge behavior as that associated with the currents of a perfectly conducting half-plane. The corresponding current behavior based on a (numerical) impedance simulation of the groove is quite different. However the resulting echowidths are comparable. Both transverse electric (TE) and transverse magnetic (TM) polarizations are treated     

Characteristic modes of a slot in a conducting cylinder and theiruse for penetration and scattering, TE case

A characteristic mode theory for slots in a circular conducting cylinder is given for calculating the characteristic magnetic currents, the equivalent magnetic current, the radiation patterns, and the fields everywhere (especially in the aperture region) of an infinitely long thin perfectly conducting cylinder with an infinitely long slot. The characteristic modes are obtained from the solution of an eigenvalue equation representing the continuity of the tangential component of the magnetic field in the slot     

Planar near-field to far-field transformation using an equivalentmagnetic current approach

An alternative method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes the near-field data to determine equivalent magnetic current sources over a fictitious planar surface that encompasses the antenna, and these currents are used to ascertain the far fields. Under certain approximations, the currents should produce the correct far fields in all regions in front of the antenna regardless of the geometry over which the near-field measurements are made. An electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents. The method of moments is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method, and in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions. Numerical results are presented for several antenna configurations     

Surface integral formulation for calculating conductor anddielectric losses of various transmission structures

The power-loss method, along with a surface integral formulation, has been used to compute the attenuation constant in microstrip and coplanar structures. This method can be used for the analysis of both open and closed structures. Using the surface equivalence principle, the waveguide walls are replaced by equivalent electric surface currents and dielectric surfaces are replaced by equivalent electric and magnetic surface currents. Enforcing the appropriate boundary condition, and E-field integral equation (EFIE) is developed for these currents. Method of moments with pulse expansion and point matching testing procedure is used to transform the integral equation into a matrix one. The relationship between the propagation constant and frequency is found from the minimum eigenvalue of the moment matrix. The eigenvector pertaining to the minimum eigenvalue gives the unknown electric and magnetic surface currents     

A comparison between two kinds of equivalent currents to analyze conducting bodies with apertures using moment methods: Application to horns with symmetry of revolution

A system of integral equations (SIE) based on the unique-hess theorem that uses only electric equivalent currents (EEC) is formulated to analyze conducting bodies with apertures. This SIE is compared with an SIE that uses both electric and magnetic equivalent currents (EMEC). In general, to solve both SIE's numerically difficult computations of Cauchy principal-value integrals with highly singular kernels are required. These integrals appear when computing electric (magnetic) fields created by magnetic (electric) currents. Their evaluation can be avoided using the EEC approach in many practical cases when the main interest is in the radiation patterns of aperture antennas. The two SIE's are compared by carrying out an analysis of rotationally symmetric horns using the moment method (MM) in its formulation for bodies of revolution. Numerical results of electric currents and radiation patterns are presented for small horns of various geometries. These results compare quite well with measurements for both SIE's. However, the central processing unit (CPU) time for the EEC formulation is an order of magnitude smaller than for the EMEC formulation.     

Stripline-fed arbitrarily shaped printed-aperture antennas

A full-wave analysis method is presented for modeling the radiation properties of a stripline-fed planar printed-aperture antenna element. In this formulation, both the finite length of stripline and the finite aperture may be of any arbitrary shape since their equivalent electric and magnetic currents are modeled with triangular patch basis functions. Galerkin's method is applied to numerically solve the coupled mixed-potential integral equation (MPIE). Exact spatial-domain Green's functions are used to account for all radiation, surface-wave, and mutual-coupling effects. Interactions between the stripline feed and the radiating aperture are rigorously included. Numerical analysis is presented for the following nonrectangular shapes: an exponentially tapered slot, an annular slot, an annular slot with opposing stubs, and a monofilar Archimedean spiral slot element. Results are shown for input return loss, radiation patterns, and axial ratio for the circularly polarized elements     

Multiple penetration of a TEz-polarized plane wave intomultilayered cylindrical cavity-backed apertures

A generalized mathematical procedure is developed for investigating a TE_z-polarized plane wave penetration through two-dimensional (2-D) multilayered cylindrical cavity-backed apertures. The mathematical treatment is based on the direct integral equation technique combined with the Galerkin's procedure. Both the near- and far-zone field solutions to such a multiple coupling system are obtained in an analytical form. By taking the aperture edge effects into account, the magnetic currents on the surrounded multiple apertures are expanded in terms of a series of Chebyshev polynomials of the first kind. Furthermore, parametric studies are performed to show the variation of the penetrated near-zone magnetic field in various cylindrical cavity-backed apertures with the aperture number and geometrical sizes