Equivalent Magnetic Current Distribution Research Articles

Radiation pattern reshaping designs for slot antenna based on the third-order mode

Based on radiation pattern reshaping technology, two slot antennas (SAs) operating on the third-order mode are designed. Both of them obtain high-gain characteristic and stable bidirectional radiation. The radiation characteristic of the SA three-order mode is analyzed. Then, the influence of the finite ground edge’s diffraction on radiation pattern of SA is considered. By using the finite ground with a suitable size, the main lobe in radiation direction can be effectively regulated. On this basis, according to the equivalent magnetic current distribution in slot, this paper proposes two radiation pattern reshaping design schemes (a. Folding rectangular slot; b. Loading C-shaped slots). Both design schemes can suppress the side lobes and regulate the main lobe in the radiation pattern. Two proposed SAs can achieve stable bidirectional radiation and obtain high-gain response. Finally, two SAs are fabricated and measured. The measured results show that two SAs achieve bidirectional radiation. The peak gains of two SAs are 6.88 dBi and 7.51 dBi, respectively.

A Standing-Wave Microstrip Leaky-Wave Antenna on EH₁/EH₃ Modes With Enhanced Broadside Gain

A conventional microstrip EH1-mode bidirectional leaky-wave antenna (LWA) usually works as a traveling wave antenna, and its typical maximum broadside gain is commonly obtained when the phase and leakage constants of the used EH1-mode are exactly equal to each other. In this article, it is, for the first time, revealed that this bidirectional LWA can alternatively operate under standing-wave states when its terminations may be open-circuited. Under some of these states, the open-terminated LWA attains higher efficiency due to the extremely small leakage constant. However, it is unfortunately illustrated that split beams are generated at these concerned states owing to the inherent opposite directions of equivalent magnetic current distributions along the two edges of the strip conductor. In order to transform the unwanted split beams into a single high-gain beam at the broadside, a novel standing-wave bidirectional LWA is presented under the operation of the hybrid EH1 and EH3 propagating modes. By analyzing the transversal electric fields of EH1- and EH3-modes, respectively, it is demonstrated that their leaky electric fields can be crucially made in an antiphase manner. Next, the EH3-mode electric field is employed to periodically replace the original EH1-mode counterpart, so as to reshape the electric fields along the two parallel radiating edges toward a desired in- phase pattern. In such a way, the appealing high-gain beam can be successfully achieved. As an example, such a hybrid-mode standing-wave bidirectional LWA is designed, simulated, and tested. The measured and simulated far-field radiation performances show excellent agreement, and they both powerfully indicate that our reported antenna has enhanced its radiation gain at the broadside compared to the conventional EH1-mode traveling-wave bidirectional LWA

Fringing field correction for spherical–rectangular microstrip antennas

This paper presents the analysis of spherical–rectangular patches using both cavity method and method of moments. A detailed procedure of cavity method is presented, including the field distribution inside the cavity, equivalent magnetic current distributions, radiation fields, effective loss tangent, and input impedance. A new fringing field correction is proposed taking into account the curvature of the patch, resulting in accurate resonance frequency.

Substrate Integrated Surface-Wave Antenna

A surface-wave antenna integrated into a substrate is investigated. The substrate-integrated surface-wave structure can be considered approximately as a dielectric slab flush-mounted in a rectangular waveguide that has the top broad wall removed. The waveguide structure is investigated rigorously through the numerical solution of a magnetic-field integral equation. It is found that the dielectric-filled structure supports an improper waveguide mode and a proper surface-wave mode. The differences between the two modes are revealed, with the propagation and radiation characteristics and the equivalent magnetic current distributions in the aperture. The improper waveguide mode has such a high attenuation constant that it cannot provide a high directivity. On the other hand, the proper surface-wave mode that has a zero attenuation constant can be used to design a high-directivity antenna. A tapered-width substrate integrated surface-wave antenna is designed, fabricated and measured. With a planar structure, the antenna can be easily fabricated and can be flush-mounted on a conductor. Measured results show that the antenna has a wide gain bandwidth and a high gain with the main beam close to endfire.

Application of Equivalence Principle for EM Scattering From Irregular Array of Arbitrarily Oriented PEC Scatterers Using Both Translation and Rotation Addition Theorems

Electromagnetic scattering from irregular array of arbitrarily oriented PEC scatterers is investigated using a novel domain decomposition method based on equivalence principle algorithm (EPA) in conjunction with addition theorems for spherical wave harmonics (SWHs). Each element is considered to be enclosed by a spherical equivalence surface as a single domain. The primary unknowns on each element are replaced by the equivalent electric and magnetic current distributions on the equivalence sphere in terms of RWG basis functions. From these current distributions, the scattered field outside its equivalence sphere is evaluated in terms of SWHs in the local coordinates system fixed to each element body. The SWHs in rotated local coordinates are translated as a new set of SWHs in other local coordinates with the same origin but axes parallel to the global coordinate’s axes using the rotation addition theorem. Furthermore, the mutual coupling effects among the separated domains are considered using the translation addition theorem for parallel local coordinate systems. It is shown that the proposed method effectively reduces the computational costs by reducing the number of unknowns versus the conventional EPA. The efficiency and validity of the proposed method are investigated through several numerical examples.

Closed-Form Expressions for the On-Axis Scattered Fields by a Subwavelength Circular Aperture in an Infinite Conducting Plane

Closed-form analytical expressions for the on-axis scattered fields by a subwavelength circular aperture in an infinite perfectly conducting plane were derived using a vector potential formulation and the equivalence principle. The final expressions are valid for the near-field, intermediate-field, and far-field zones. The underlined formulation is based on the equivalent quasi-static magnetic current distributions in the aperture, which were derived by Bethe and Bouwkamp in the mid 40's and early 50's. The resulting scattered-field integrals, which involve the free-space Green's function, were evaluated analytically after introducing Taylor series expansion and using transformations. The final closed-form expressions of the scattered fields are given in terms of a recursion formula. Obtained results based on these closed-form expressions are in excellent agreement with data generated by a numerical integration scheme.

Quasi‐TEM Rectangular Waveguides with Frequency Selective Surface Walls: Part II—Physical Mechanism

ABSTRACTThe physical mechanism of quasi‐TEM (transverse electromagnetic) waveguides with frequency selective surface (FSS) walls is established on the basis of an equivalent magnetic current technique in this paper. The equivalent magnetic current distributions in the slots of dielectric surfaces with dipole‐FSS walls and dielectric surface of bare‐slab, as well as hexagonal crystal FSS walls, are presented and discussed. This study shows that the electromagnetic fields in waveguide are mainly radiated from the concurrent magnetic current bands in longitudinal slots. The relationship between the uniformity of electromagnetic fields and the phase variation of longitudinal magnetic currents is discussed. The electrical properties and mechanism of quasi‐TEM rectangular waveguides with slotlines are also investigated to confirm the proposed mechanism. Three categories of periodic structure, which are potentially useful as artificial magnetic conductor, are investigated, and the required conditions to realize quasi‐TEM mode in rectangular waveguide are proposed. Copyright © 2013 John Wiley & Sons, Ltd.

Method of Moments Analysis of Slotted Substrate Integrated Waveguide Arrays

A method of moments analysis is described for substrate integrated waveguide slot arrays. The array structure is modeled as a parallel plate waveguide on which via holes and slots are created. The field into the waveguide is expressed by the sum of the parallel plate's contribution and the field scattered by the metallic through holes, with both contributions expressed by means of an expansion in terms of vectorial cylindrical eigenfunctions. The slots are modeled as unknown equivalent magnetic current distributions which are found by solving an integral equation derived from the continuity of the field on the slot surface. Antenna arrays already presented in the literature will be analyzed, and the results compared with HFSS simulations. It will be shown that the proposed method is efficient and gives results in excellent agreement with the most common simulation tools.

Analysis of Substrate Integrated Waveguide Structures Based on the Parallel-Plate Waveguide Green's Function

This paper presents the full-wave characterization of substrate integrated waveguide structures. Substrate integrated circuits are considered as an ensemble of conducting posts placed in a parallel-plate waveguide and are analyzed in terms of the cavities formed by the top and bottom conducting plates and by the walls of the metallic vias. The field inside the parallel-plate waveguide is computed by considering the dyadic Green's function expressed as an expansion in terms of vectorial cylindrical eigenfunctions and considering the scattering from the ensemble of conducting posts. Coaxial or waveguide ports are included in the analysis as equivalent magnetic current distributions. Self-admittance and mutual admittance are calculated in a form that separates the parallel-plate contribution from the field scattered by the posts. Results relevant to structures already presented in literature will be shown and compared with simulations obtained with one of the most used articles of commercial software. It will be shown that an excellent agreement with published results is achieved together with significant improvements both in computational time and memory requirements.

Studies of small dualband annular‐ring slot antenna with a pair of implanted spur‐like slits

AbstractIn this article, a compact annular‐ring slot antenna for dualband operations is proposed and studied. A pair of spur‐like slits was implanted in the center patch of an annular‐ring slot antenna to excite two resonant modes with their resonant frequencies easily adjusted by changing the dimensions of these slits, resulting in a large range of dual‐frequency ratios (1.07–2.2). For the first excited resonant mode, the routes of the equivalent magnetic current distribution in the slot region can be lengthened by these slits. The resultant lowered first resonant‐band center frequency (from that of the unperturbed annular‐ring slot antenna) thus made the proposed antenna effectively miniaturized. The proposed antenna was found to have very good linearly polarized broadside radiation patterns and very low cross polarization levels in both operating bands.© 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1578–1581, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22536

RCS computation for a large array of waveguide slots with finite wall thickness using the MoM accelerated by P-FFT algorithm

This correspondence presents an accurate and efficient method of moments (MoM) for analyzing electromagnetic scattering by a large finite array of waveguide slots with finite thickness. In this method, the mixed potential integral equation (MPIE) is utilized onto both upper and lower surfaces of the slots, and the subdomain MoM procedure is implemented to obtain the equivalent magnetic current distributions. The precorrected fast Fourier transform (P-FFT) method is employed to accelerate the entire computational process to reduce significantly the memory requirements for large arrays. During the MoM procedure, the Rao-Wilton-Glisson (RWG) functions are used as the basis and testing functions, with both z- and x-directional magnetic currents considered. This approach extends applicability of the present method to solve the MPIE for characterizing waveguide slots of arbitrary shape and distribution and the capability of the integral equation based fast algorithm. Numerical results are obtained and compared with the experimental results, to verify the accuracy and efficiency of this technique.

Shorted elliptical patch antennas with reduced surface waves on two frequency bands

In this paper, a study on the surface waves emission of a shorted annular elliptical patch (SAEP) antenna is presented. This radiator is constituted of an annular elliptical patch having the inner border shorted to the ground plane. The surface wave field excited by the SAEP antenna has been evaluated considering an equivalent magnetic current distribution flowing onto the outer boundary of the patch. It will be demonstrated that the dimensions of the outer elliptical contour can be chosen in such a way that the excitation of the TM/sub 0/ surface wave mode is suppressed on two frequencies. This characteristic makes possible the design of SAEP antennas with reduced surface wave (RSW) emissions on two frequency bands. To validate this result both numerical simulations and measurements will be presented. In particular, it will be shown that when the RSW-SAEP is considered the field strength within the substrate undergoes a faster decay resulting in a reduced mutual coupling in dual band array applications. Furthermore, the effective reduction of the surface waves power minimizes the scattering from the ground plane edges leading in smoother radiation patterns.

Radial field retrieval for current reconstruction from spherical acquisition

An iterative algorithm for the retrieval of the radial component of the electric field is presented in conjunction with an efficient reconstruction algorithm to calculate an equivalent magnetic current (EMC) distribution from the electric field components obtained in a spherical acquisition.

A hybrid UTD‐MM analysis of the radiation from a composite slot‐blade cavity‐backed antenna on realistic aircraft configurations

A hybrid method which combines the uniform geometrical theory of diffraction (UTD) with a numerical moment method (MM) technique is presented for the analysis of the radiation from a composite slot‐blade cavity‐backed antenna located on realistic aircraft configurations. The excitation of the antenna is due to a delta gap generator in a thin‐wire probe feed that is placed inside a rectangular cavity. The MM procedure is used to solve coupled integral equations that are formulated for the unknown equivalent electric current distribution on the blade and the unknown equivalent magnetic current distribution over the slot, when this slot‐blade antenna configuration resides on an infinite ground plane. The UTD is next used to efficiently and accurately calculate the radiation from these equivalent current distributions for the slot‐blade antenna combination when the latter are now located on realistic aircraft geometries instead of a fiat ground plane. Calculated radiation patterns of the composite slot‐blade cavity‐backed antennas placed on a Boeing 737 commercial airplane and an F‐16 fighter aircraft are presented to illustrate the utility of this hybrid approach.

Computations for radiation and surface-wave losses in coplanar waveguide bandpass filters

A new approach is developed to simulate both radiation and surface-wave losses in general coplanar waveguide (CPW) discontinuity structures. The newly derived formulas are concise, simple, and efficient for computation. Full-wave characterization of CPW filter structures are first accomplished by the mixed-potential integral equation and the method of moments. Given equivalent magnetic-current distributions on the apertures of a CPW, the matrix pencil approach is applied to extract the scattering parameters and the new formulas are employed to obtain the losses and far-field patterns of the space-wave radiation and surface wave. Simulation of the calculated radiation and surface-wave losses by field theory is found to be consistent to the total power loss determined from the scattering parameters by circuit theory, which verifies the correctness of our new expressions.

A numerically efficient technique for the analysis of slots in multilayer media

A numerically efficient technique for the analysis of slot geometries in multilayer media is presented using closed-form Green's functions in spatial domain in conjunction with the method of moments (MoM). The slot is represented by an equivalent magnetic-current distribution, which is then used to determine the total power crossing through the slot and the input impedance. In order to calculate power and current distribution, spatial-domain closed-form Green's functions are expanded as power series of the radial distance /spl rho/, which makes the analytical evaluation of the spatial-domain integrals possible, saving a considerable amount of computation time.

Full‐wave spectral‐domain analysis of coplanar discontinuities using numerically matched loads

AbstractThis article presents a full‐wave analysis of coplanar waveguide discontinuities using a spectral‐domain approach. Based on a magnetic field integral formulation, the equivalent magnetic current distribution on the apertures is solved by a moment method. The scattering parameters are numerically measured with the help of numerically matched loads placed at each port of the discontinuities. © 1995 John Wiley & Sons. Inc.

Full-wave characterization of the mode conversion in a coplanar waveguide right-angled bend

A full-wave algorithm is proposed to analyze thoroughly a 90/spl deg/ bend of coplanar waveguide (CPW). Based on the mixed potential integral equation (MPIE) formulation, the equivalent magnetic current distribution on the apertures is solved by the moment method using overlapping rooftop basis functions and the Galerkln weighting procedure. The matrix pencil approach is then utilized to do the de-embedding procedure and extract both the coplanar and slotline modes scattering off the asymmetric discontinuity. Experiments are performed to measure the scattering parameters and the results verify the accuracy of the present algorithm. The full 4/spl times/4 scattering matrix between these two modes is presented from which the occurrence of the mode conversion is investigated. The mode conversion is noticed to become almost complete at certain frequencies, which may be useful in the design of CPW to coupled slotline transition. >

'Thermic end-fire' interstitial applicator for microwave hyperthermia

The analysis of a thermic end-fire interstitial applicator for microwave hyperthermai, i.e. an applicator that performs a tip-localized heating of the surrounding lossy medium, is presented. The antenna consists of a shorted coaxial cable with an annular radiating aperture at the end. the analytical approach is based on the equivalence principle, which leads to an integral equation for the equivalent magnetic current distribution on the aperture; solution is achieved by the method of moments. All theoretical results are compared to experimental ones, showing a good agreement in a wide frequency range.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Scattering from Narrow Grooves and Slits

Analytical expressions are derived for the equivalent magnetic current distributions over the apertures of filled grooves and slits in a thick ground plane. These are obtained via a low frequency solution of the exact integral equations and exhibit the expected edge behavior at the groove or slit terminations. They are used to derive closed-form expressions for the associated characteristic parameters such as aperture potentials, aperture admittances, transfer admittances, radar echo widths, and transmitted powers. Both principal polarizations are treated and the results are potentially useful in constructing suitable models for long and narrow three-dimensional structures.