Analysis of the cylindrical-rectangular patch antenna

An analysis is presented of a thin cylindrical-rectangular microstrip patch antenna. After obtaining the electric field under the curved patch and the resonant frequencies using the cavity model, the far-field is found by considering the equivalent magnetic current radiating in the presence of a cylindrical surface. The input impedance and the total Q-factor are then calculated. Numerical and graphical results are presented to illustrate the effect of curvature on the characteristics of the TM₁₀ and TM₀₁ modes     

Characteristics of aperture coupled microstrip antennas withvarious radiating patches and coupling apertures

A full wave moment method is applied to the analysis of aperture coupled microstrip antennas, in which all components of the electric and equivalent magnetic surface currents are considered. The electric current distributions on the rectangular patch for different coupling aperture positions are presented with their radiation patterns. The effects of the coupling aperture shape and size on the input impedance and radiation performance are also discussed. As an example of new radiators, slotted patches are studied, and it is shown that they can be used to achieve dual-frequency operation     

Waveguide excited microstrip patch antenna-theory and experiment

An arbitrarily shaped microstrip patch antenna excited through an arbitrarily shaped aperture in the mouth of a rectangular waveguide is investigated theoretically and experimentally. The metallic patch resides on a dielectric substrate grounded by the waveguide flange and may be covered by a dielectric superstrate. The substrate (and superstrate, if present) consists of one or more planar, homogeneous layers, which may exhibit uniaxial anisotropy. The analysis is based on the space domain integral equation approach. More specifically, the Green's functions for the layered medium and the waveguide are used to formulate a coupled set of integral equations for the patch current and the aperture electric field. The layered medium Green's function is expressed in terms of Sommerfeld-type integrals and the waveguide Green's function in terms of Floquet series, which are both accelerated to reduce the computational effort. The coupled integral equations are solved by the method of moments using vector basis functions defined over triangular subdomains. The dominant mode reflection coefficient in the waveguide and the far-field radiation patterns are then found from the computed aperture field and patch current distributions. The radar cross section (RCS) of a plane-wave excited structure is obtained in a like manner. Sample numerical results are presented and are found to be in good agreement with measurements and with published data     

On the electromagnetic field in a cavity fed by a tangentialelectric field in an aperture in its wall

Heretofore, the electromagnetic field produced by a specified tangential electric field in an aperture in the wall of an arbitrarily shaped cavity has most often been expanded in terms of cavity modes. An alternative approach, that of the electric field integral equation is presented. In this approach, the cavity field is expressed as the field of a surface density of tangential electric current, or a surface density of tangential magnetic current, or a combination of surface densities of tangential electric and magnetic currents on the boundary of the cavity. Each surface density is characterized by a single tangential vector function which is determined by the integral equation requiring that the part of the electric field tangent to the boundary of the cavity must reduce to the specified tangential electric field in the aperture and zero elsewhere on the boundary of the cavity. The electric field integral equation method is specialized to more easily determine the field inside an arbitrary cylindrical cavity excited by a tangential electric field in an aperture in its lateral wall. The method is further specialized to a circular cavity     

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     

Effects of finite ground plane on the radiation characteristics ofa circular patch antenna

An analytical technique to determine the effects of finite ground plane on the radiation characteristics of a microstrip antenna is presented. The induced currents on the ground plane and on the upper surface of the patch are determined from the discontinuity of the near field produced by the equivalent magnetic current source on the physical aperture of the patch. The radiated fields contributed by the induced current on the ground plane and the equivalent sources on the physical aperture yield the radiation pattern of the antenna. Radiation patterns of the circular patch with finite ground plane size are computed and compared with the experimental data, and the agreement is found to be good. The radiation pattern, directive gain and input impedance are found to vary widely with the ground plane size     

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     

Electromagnetic scattering from an arbitrarily shaped three-dimensional homogeneous chiral body

The method of moments technique for analyzing electromagnetic scattering from an arbitrarily shaped three-dimensional homogeneous chiral body is presented based on the combined field integral equations. The body is assumed to be illuminated by a plane wave. The surface equivalence principle is used to replace the body by equivalent electric and magnetic surface currents. These currents radiating in unbounded free space produce the correct scattered field outside. The negatives of these currents produce the correct total internal field, when radiating in an unbounded chiral medium. By enforcing the continuity of the tangential components of the total electric and magnetic fields on the surface of the body, a set of coupled integral equations is obtained for the equivalent surface currents. The surface of the body is modeled using triangular patches. The triangular rooftop vector expansion functions are used for both equivalent surface currents. The coefficients of these expansion functions are obtained using the method of moments. The mixed potential formulation for a chiral medium is developed and used to obtain explicit expressions for the electric and magnetic fields produced by surface currents. Numerical results for bistatic radar cross sections are presented for three chiral scatterers - a sphere, a finite circular cylinder, and a cube.     

Characteristics of a longitudinal/transverse coupling slot incrossed rectangular waveguides

A rigorous analysis of a broad-wall slot coupler between two crossed rectangular waveguides is presented. The slot is longitudinal and offset from the center line in the main guide and is centered transverse in the branch guide. Integral equations are developed, taking into account finite wall thickness. The integral equations are then solved for the aperture electric field. Coupling slot characteristics are obtained, including the resonant length and dominant mode scattering. Numerical results for resonant length and scattering parameters are presented over a range of offsets, waveguide dimensions, and frequencies     

Absorption Characteristics of Prolate Spheroidal Models Exposed to the Near Fields of Electrically Small Apertures

Irradiation of prolate spheroidal models of biological models by the near fields of electrically small apertures is analyzed. The solution procedure involves the replacement of the aperture source by an equivalent configuration of electric and magnetic dipoles. The specific absorption rate (SAR) induced in the irradiated object is then calculated using the extended boundary condition method (EBCM). Numerical results are presented for the exposure case where the incident electric field at the spheroid location is parallel to the major axis of the model. This polarization is associated with the maximum low-frequency absorption in biological models and, hence, is the most important polarization case in microwave dosimetry.     

Electromagnetic radiation and scattering from finite conducting anddielectric structures: surface/surface formulation

An efficient and accurate numerical procedure for the analysis of the electromagnetic scattering and radiation from arbitrarily shaped, composite finite conducting and dielectric bodies is proposed. A set of coupled electric field integral equations involving surface equivalent electric and magnetic currents is used. The coupled integral equations are solved through planar triangular patch modeling and the method of moments. Two separate, mutually orthogonal vector functions for each edge connecting a pair of triangular patches have been developed. Numerical results for disk/cone and cylinder/cone structures are compared with other available data. Limited comparison with experimental data has also been made     

Electric and Magnetic Coupling through Small Apertures in Shield Walls of Any Thickness

A method is presented for evaluating the coupling between two identical resonant cavities coupled by a small aperture in a plane common wall of arbitrary thickness. The coupling is related to the frequencies of the symmetric and asymmetric modes of oscillation of the coupled cavity structure, and a variational technique is used to determine those frequencies. The method is applied to circular and rectangular apertures, and it is shown that the coupling is separable into electric and magnetic terms. The results enable theoretical solutions to be obtained for the electric and magnetic polarizabilities of circular and rectangular apertures in walls of zero thickness, and equivalent polarizabilities to be obtained when the wall thickness is nonzero. Curves of numerical values are given for circular and rectangular apertures. With zero wall thickness, the results obtained are the same as those of Bethe for a circular aperture and give good agreement with Cohn's experimental results for rectangular apertures.     

Microstrip patch designs that do not excite surface waves

Two variations of a circular microstrip patch design are presented which excite very little surface wave power. Both of the designs are based on the principle that a ring of magnetic current in a substrate (which models the patches) will not excite the dominant TM₀ surface wave if the radius of the ring is a particular critical value. Numerical results for radiation efficiency and radiated field strength from a ring of magnetic current are shown to verify this basic design principle. The proposed patch designs are chosen to have a radius equal to this critical value, while maintaining resonance at the design frequency. The designs excite very little surface-wave power, and thus have smoother radiation patterns when mounted on finite-size ground planes, due to reduced surface-wave diffraction. They also have reduced mutual coupling, due to the reduced surface-wave excitation. Measured results for radiation patterns and field strength within the substrate are presented to verify the theoretical concepts     

The equivalent parameters for the radiating slot on a sectoralwaveguide

Formulas for the field components of the TE_pq, mode and the dominant mode TE₁₁ in a sectoral waveguide are given. Using the equivalence principle, the electric field distribution on the aperture surface of a narrow longitudinal slot cut in the curved broad wall of a sectoral waveguide is solved by the moment method (Galerkin's method). Important results such as the scattering parameters, the equivalent shunt admittance, and the resonant conductance and length are studied. The method used in this paper has good precision and has been adopted in the design of a linear slot array     

Effect of substrate on the efficiency of an arbitrarily shaped microstrip patch antenna

A general approach is presented for the determination of power radiated via the space wave and surface wave from the aperture of an arbitrarily shaped microstrip antenna. The magnetic current model is used for this, and the analysis is carried out in the Fourier domain to determine the effect of the substrate. It has been shown that, in the Fourier domain, the longitudinal components of electric and magnetic displacement vectors follow the transmission line equation and can be solved by inspection. An expression for total radiated power has been derived. The singularities of the integral for power radiation indicate the presence of surface wave modes, and the associated power has been obtained using a singularity extraction technique. The effect of the substrate on space wave power has also been determined. This theory has been applied to a rectangular patch antenna. The results are in conformity with those reported in the literature. It has been found that for the frequency range (h/lambda, < 0.02), the effect of dielectric substrate can be neglected.     

Direct analytical solution for the electric field distribution atthe conductor surfaces of coplanar waveguides

A new analytical method of evaluating the electric field distribution across the conductor surfaces of coplanar waveguides (CPWs) is presented. Here, a series of conformal mappings are used to transform the CPW's geometry and field distribution into a uniform image domain, to facilitate a direct field solution. The cumulative electric flux distribution across each conductor surface within the dielectric substrate is studied, and its effects on coupling and propagation modes are described. Direct solutions for the quasi-static normal electric field components are presented together with their graphical representations. Numerical computations show how the total electric flux terminating on the CPW's conductor surfaces varies in terms of the CPW's geometry and substrate parameters     

The equivalence of the electric and magnetic surface current approaches in microstrip antenna studies

It is shown that the fields produced by the electric surface currents on the conducting patch of a microstrip antenna are equivalent to those produced by a magnetic surface current sheet bounding the patch in the substrate only when dyadic Green's functions for the two-layer stratified medium are used.     

Characteristics of the cylindrical-circular patch antenna

An analysis of a thin cylindrical-circular microstrip patch antenna is presented. Using the cavity model as a base, formulas are obtained for the far-zone electric field and the input impedance of a coax-fed patch. Numerical and graphical results are given to illustrate the effects of curvature on the characteristics of the TM₁₁ mode     

基于裂缝谐振环周期结构的频率选择表面

介绍了一种利用裂缝谐振环构成的缝隙型频率选择表面。使用有限元法对这种频率选择表面的电波传输特性进行了全波仿真分析。同时,提出了简单的L-C等效电路模型,并结合巴比涅原理分析预测了这种频率选择表面的谐振频率。分析结果表明,频率选择表面的谐振频率由单元结构决定,受单元周期的影响较小,而且透射波具有沿垂直于裂缝方向的极化选择性。实验测量结果与理论分析吻合。     

小孔耦合的带状线耦合器

本文利用保角变换求势函数的方法,导出了带状线中的归一化电场分布的封闭形表示式。根据小孔耦合理论给出了带状线间通过公共壁上圆孔耦合的耦合度表示式。实验表明理论值和实验结果间具有良好的一致性。