Aperture coupled stripline coupler

Analytical expressions for coupling between two striplines, coupled through small apertures in the form of narrow rectangular slot and circular hole, are derived. The experimental results are presented along with theoretical results.     

TE-case RCS analysis of finite-thickness slotted circular cylinder loaded with lossy filling

A generalized model is developed to study the TE-polarized plane wave scattering by coated and uncoated slotted circular cylinders of nonzero thickness and by a filled and not filled circular cylinders with sectorial cuttings. The mathematical treatment is based on the coupled integral equations (IEs) with respect to the tangential electric field at the slot/cutting apertures. The Galerkin method with weighted Gegenbauer polynomials as basis functions is used to convert IEs to a set of linear algebraic equations. Numerical simulations of the radar cross section (RCS) are carried out in the case of single slot/cutting in order to reveal the effect of thickness. Potentials of three approximations to the field in the slot/cutting domain are studied. Their use enables one to substantially accelerate the RCS calculations.     

EMI from cavity modes of shielding enclosures-FDTD modeling andmeasurements

Electromagnetic interference (EMI) from slots and apertures resulting from coupling of interior sources through enclosure cavity modes in a rectangular test enclosure is reported. EMI from a specially designed test enclosure with slots or apertures excited by interior sources was studied experimentally and with finite-difference time-domain (FDTD) modeling. The measurements and FDTD modeling agree well. The results indicate that radiation at cavity mode resonances through slots and apertures of nonresonant dimensions can be as significant as the radiation at aperture or slot resonances. The agreement between the FDTD modeling and measurements demonstrates the usefulness of FDTD for investigating aspects of shielding enclosure design such as coupling to slots and apertures and slot interactions     

Coupled Transmission Lines

An analysis of coupling between a stripline and a rectangular waveguide is presented. Coupling is through small apertures in the form of a circular hole or a narrow rectangular slot. A closed form expression for the normalized field distribution in the stripline, required for the purpose of analysis, is also derived. The theoretical results show good agreement with the experimental results.     

Investigation of the mutual coupling between apertures on doubly curved convex surfaces: theory and measurements

A hybrid method of high-frequency approximation (UTD) and method of moments is used to calculate the mutual coupling between circular apertures on a doubly curved surface. This requires that the geodesics on doubly curved surfaces be found. To represent the aperture fields, a single waveguide mode approximation is used. In order to verify the theoretical results, a general paraboloid of revolution with circular waveguide-fed apertures was built at Ericsson Microwave Systems AB, Molndal, Sweden. This has given a possibility to verify the theoretical model for a general doubly curved surface against measurements. To the authors' knowledge, no such verification is available in the literature. It was found that measured and theoretical results in terms of mutual coupling agree very well for copolar coupling. As expected, the mutual coupling results are very dependent on the polarization. In fact, the definition of polarization directions and the need for polarization control are important issues for doubly curved conformal array antennas.     

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.     

A bound on EMP coupling

A bound on the energy coupled to a load by means of an antenna or aperture subjected to a step function electromagnetic pulse (EMP) is given by the polarizabilities of the antenna or aperture. Examples of coupling bounds for a slender electric dipole antenna, a circular aperture, and a narrow slot aperture with depth are given. It is demonstrated, by use of the bound on the integral of the effective area over all frequencies, that the maximum energy absorbed by an object subjected to a step function EMP is bounded in terms of the static polarizabilities of the object. (The energy spectrum of the step function EMP bounds the spectrum of EMP described by the double exponential over all frequencies.) It is demonstrated that this bound can be used on apertures in infinite ground planes for which Babinet's principle fails to apply (apertures having depth and cavity backed apertures), where the requirement is simply to use the polarizabilities on the incident side of the aperture.<>     

Electromagnetic coupling through small apertures in a conducting screen

The electromagnetic field coupling through small apertures illuminated by an arbitrary incident plane wave is discussed for general aperture shapes. A set of new integral equations in a form highly amenable to numerical solution techniques is derived. Based on the application of the Rayleigh series method, an analytical solution is obtained for the first few terms of the expansion of the apertureE- field of a circular aperture. Numerical results are also constructed for the aperture field and the diffracted field of small rectangular apertures and compared with those of the circular apertures.     

Slot-coupled microstrip antenna for broadband circular polarisation

A microstrip antenna with broadband circular polarisation (CP) is presented. The proposed microstrip antenna has a circular patch and is excited by a series microstrip-line-feed configuration through the coupling of a ring slot in the ground plane. The broadband operation is achieved by coupling two CP resonant elements, which are due to the circular patch and the ring slot, respectively. A typical prototype using foam material of thickness 5 mm as the antenna substrate is constructed. Measured results show the 3 dB-axial-ratio bandwidth centred at 2500 MHz is more than 10%.     

Coupling through tortuous path narrow slot apertures into complexcavities

A hybrid finite-element method/method of moments (FEM/MOM) model has been implemented to compute the coupling of fields into a cavity through narrow slot apertures having depth. The model utilizes the slot model of Warne and Chen (1988, 1989, 1990, 1992), which takes into account the depth of the slot, wall losses, and dielectrics with air gaps in the slot region. The cavity interior is modeled with the mixed-order covariant-projection elements of Crowley (1988). Results are given showing the accuracy and generality of the method for modeling geometrically complex slot-cavity combinations     

Mutual admittance between slots in cylinders of arbitrary shape

A numerical formulation involving the Fourier transform and the combined-field integral equation is presented to calculate the mutual admittance between axial slots or circumferential slots in arbitrarily shaped cylinders. Two cases are considered: coupling between two circumferential slots and coupling between two axial slots. The slots are assumed to be waveguide-fed apertures excited with the TE₁₀ waveguide mode, with no higher-order modes included in the model. The combined field-integral equation (CFIE) formulation was used in conjunction with the magnetic field integral equation (MFIE) to solve the resulting two-dimensional integral equation. Formulations for the axial slot case are discussed. Results concerning the discretization and truncation of the spectrum, as well as the accuracy of the procedure, are presented for both axial and circumferential cases. The accuracy of the procedure is demonstrated by comparison with eigenfunction data for circular cylinders     

Electromagnetic transmission through multiple circular apertures in a thick conducting plane

The boundary-value problem of electromagnetic wave scattering from multiple circular apertures in a thick conducting plane is rigorously solved. The eigenfunction expansion, integral transform, and superposition principle are utilized to represent the scattered field in the discrete and continuous modes. The boundary conditions are enforced to obtain a set of simultaneous equations for the discrete modal coefficients. The transmission coefficient is represented in a fast convergent series. Computation is performed to illustrate the behavior of transmission and coupling through multiple circular apertures in terms of the aperture geometry.     

Electromagnetic transmission through apertures in a cavity in a thick conductor

The problem of electromagnetic coupling from one region to another through an aperture-to-cavity-to-aperture system is specialized to the case of electrically small circular apertures on the axis of a cylindrical cavity of circular cross section for the transverse electromagnetic (TEM) and transverse electric (TE) cases. A simple equivalent circuit for the coupling system is developed. It is found that for certain cavity depths an exceptionally large amount of electromagnetic energy can be transmitted, and that for identical apertures the transmission cross section of the system is independent of the common radius of the apertures as well as the radius of the cavity.     

Mutual coupling in a finite planar array of circular apertures

Equations are presented for the calculation of the interelement mutual coupling in a finite size planar array of waveguide-fed apertures in an infinite flat conductor. The general mutual admittance expression is evaluated for circular apertures and the mutual coupling calculations are verified experimentally for twoTE_{11}mode excited apertures. Qualitative agreement between calculations for a 183 element array and an infinite array establishes the validity of the finite array theoretical model.     

Mutual coupling between circular waveguide-fed apertures in a rectangular ground plane

A method is presented whereby the infinite ground plane analytical model for the self- and mutual admittances of waveguide-fed apertures can be supplemented (using the geometrical theory of diffraction) to include the edge effects of a rectangular ground plane. TheH-plane coupling between twoTE_{11}mode excited circular apertures is calculated and compared with measurements.     

电磁脉冲通过孔缝到系统内部的耦合约束

介绍了核电磁脉冲通过孔缝耦合到系统内部的最大能量计算方法，给出了倒指数型电磁脉冲最大耦合能量的解析表达式。该模型在定孔总截面正比于波频率4次方时，计算出通过孔耦合到腔体内部的最大能量，实现电磁耦合能量的计算。倒指数脉冲模型的理论计算结果，可以对电子设备电磁脉冲的保护具有重要意义。     

Measuring the transfer impedance and admittance of a cylindricalshield using a single triaxial or quadraxial fixture

An experimental procedure is proposed for quickly measuring both the transfer impedance and admittance of cylindrical shields using a single triaxial or quadraxial fixture. The approach is demonstrated for circular apertures, longitudinal slots, and longitudinal strips. It is anticipated that this approach can be used to completely characterize shield faults that are intentionally introduced to increase the electromagnetic coupling to interior circuits in order to demonstrate hardness margin     

Analysis of rotationally symmetric arrays of apertures onconducting spherical surfaces

Rotationally symmetric arrays of circular waveguide fed apertures on conducting spherical surfaces have been analyzed. Representation of the outside electromagnetic fields in terms of spherical transmission line modes permits the array analysis to be viewed as a spherical waveguide junction discontinuity problem. The apertures, in general, carry dual polarized circular waveguide TE₁₁ modes. Two independent formulations-the unit cell method and the eigen excitation method, which take rotational symmetry into account-are developed and are checked against each other numerically for computational accuracy. These two formulations are analytically linked as discrete Fourier series pairs. It is seen that mutual coupling along the array decays more rapidly when the polarization of excitation is perpendicular to the array plane than when it is parallel to it. This analysis has been applied in the performance analysis of the dome lens phased array radar antenna     

An approximate solution for E-polarization coupling into acoaxial cylinder with an infinite axial slot

An approximate solution is derived for determining the total current induced on a centrally located conducting wire within a two-dimensional axially slotted cylinder for the case of E-polarization. Its validity is tested against a full moment-method numerical solution of the describing integral equation. The derivation of the approximate solution is similar to the hollow-cylinder case presented by P.M. Morse and H. Feshbach (195) in that the same basic form for the aperture distribution is assumed. A rapidly converging series solution is developed which is shown to be valid for an electrically `narrow' slot (accurate for apertures up to one wavelength wide) over a rather broad frequency spectrum. Though the aperture must be electrically narrow, many practical coupling problems of interest can be accommodated. Useful insight into coupling phenomena is obtained by direct inspection of the solution, and some novel observations about the current response are made     

Stripline to microstrip line aperture coupler

Aperture coupling between stripline and microstrip line is analyzed as a function of the electric and magnetic polarizabilities of the aperture, using Bethe's small-aperture coupling theory. A coupling expression for the general case of an aperture in the common ground plane is derived. Coupling variations with aperture dimensions for the case of a thin slot, a hole, a diamond, a rounded end slot, and an ellipse are determined using McDonald's polynomial approximations for the electric and magnetic polarizability for small apertures. Experimental results for the case of a thin slot and a circuit aperture are also presented