395 research outputs found
Novel Microstrip Fed Mechanically Tunable Combline Cavity Filter
Cataloged from PDF version of article.A novel configuration for mechanically tunable combline bandpass filters is proposed, where the classical resonating rod-tuning screw combination is replaced with a simple printed circuit-tuning screw combination. Moreover, because a printed circuit structure that uses metal vias forms the bottom part of the cavity, the coaxial type feeding and the coaxial to cavity matching of classical combline filters are also replaced with a microstrip feeding. Consequently, the proposed configuration provides smaller size, less weight, integration with other printed circuits and significant simplification in the fabrication process. A prototype filter is designed and fabricated for verification. The measured results are in good agreement with the simulation, and the filter exhibits very good harmonic suppression. © 2013 IEEE
Analysis of Input Impedance and Mutual Coupling of Microstrip Antennas on Multilayered Circular Cylinders Using Closed-Form Green’s Function Representations
Cataloged from PDF version of article.Closed-form Green’s function (CFGF) representations for cylindrically stratified media are developed and used in conjunction with a Galerkinmethod ofmoments (MoM)in the space domain for the analysis of microstrip antennas on multilayered circular
cylinders. An attachment mode is used in the MoM solution procedure to accurately model the feeding of probe-fed microstrip
antennas. The developed CFGF representations are modified in the source region (where two current modes can partially or fully overlap with each other during the MoM procedure) so that singularities can be treated analytically and hence, the proposed CFGF
representations can be safely used in this region. Furthermore, accurate CFGF representations for the probe-related components
(necessary for probe type excitations including the attachment mode) are obtained when the radial distance between the source
and field points is electrically small or zero. Numerical results in the form of input impedance of various microstrip antennas and the
mutual coupling between two antennas are presented showing good agreement when compared to the available published results as well
as the results obtained from CST Microwave Studio
Application of iterative techniques for electromagnetic scattering from dielectric random and reentrant rough surfaces
Cataloged from PDF version of article.Stationary [e.g., forward–backward method (FBM)]
and nonstationary [e.g., conjugate gradient squared, quasi-minimal
residual, and biconjugate gradient stabilized (Bi-CGSTAB)]
iterative techniques are applied to the solution of electromagnetic
wave scattering from dielectric random rough surfaces with arbitrary
complex dielectric constants. The convergence issues as well
as the efficiency and accuracy of all the approaches considered
in this paper are investigated by comparing obtained scattering
(in the form of normalized radar cross section) and surface field
values with the numerically exact solution, computed by employing
the conventional method of moments. It has been observed
that similar to perfectly and imperfectly conducting rough surface
cases, the stationary iterative FBM converges faster when applied
to geometries yielding best conditioned systems but exhibits
convergence difficulties for general geometries due to its inherit
limitations. However, nonstationary techniques are, in general,
more robust when applied to arbitrarily general dielectric random
rough surfaces, which yield more ill-conditioned systems. Therefore,
they might prove to be more suitable for general scattering
problems. Besides, as opposed to the perfectly and imperfectly
conducting rough surface cases, the Bi-CGSTAB method and FBM
show two interesting behaviors for dielectric rough surface pro-
files: 1) FBM generally converges for reentrant surfaces when the
vertical polarization is considered and 2) the Bi-CGSTAB method
has a peculiar convergence problem for horizontal polarization.
Unlike the other nonstationary iterative techniques used in this
paper, where a Jacobi preconditioner is used, convergent results
are obtained by using a block-diagonal preconditioner
SIW based interdigital bandpass filter with harmonic suppression
Cataloged from PDF version of article.A novel configuration of interdigital bandpass filter based on the substrate integrated waveguide (SIW) technology is proposed. In addition to the interdigital resonators in SIW that determine the main response/characteristics of the filter, narrowing the width of the SIW at the center of the filter and additional vias at its input and output parts act as two additional control mechanisms to achieve the desired filter response. Moreover, dumbbells are etched to the ground side of the microstrip feeding sections at both ends of the filter to improve its harmonic suppression. A prototype filter is designed and fabricated for verification. The measured results are in good agreement with the simulations, and the filter exhibits very good harmonic suppression. (c) 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:66-69, 201
Optical antenna of comb-shaped split ring architecture for increased field localization in NIR and MIR
Cataloged from PDF version of article.We propose and demonstrate novel designs of optical antennas based on comb-shaped split ring architecture that display multi resonance field intensity enhancement spectrum. These nanoantennas achieve substantially increased field localization at longer wavelengths than that of a single or an array of dipoles with the same side length. With these optical antennas, localizing near infrared (NIR) and mid infrared (MIR) lights within a region of tens of nanometers at an intensity enhancement level of the order of thousands of magnitude can be accomplished. (C)2013 Optical Society of America
Three-dimensional study of planar optical antennas made of split-ring architecture outperforming dipole antennas for increased field localization
Cataloged from PDF version of article.Optical antennas are of fundamental importance for the strongly localizing field beyond the diffraction limit. We report that planar optical antennas made of split-ring architecture are numerically found in three-dimensional simulations to outperform dipole antennas for the enhancement of localized field intensity inside their gap regions. The computational results (finite-difference time-domain) indicate that the resulting field localization, which is of the order of many thousandfold, in the case of the split-ring resonators is at least 2 times stronger than the one in the dipole antennas resonant at the same operating wavelength, while the two antenna types feature the same gap size and tip sharpness. (C) 2012 Optical Society of Americ
Efficient computation of surface fields excited on a dielectric-coated circular cylinder
Cataloged from PDF version of article.An efficient method to evaluate the surface fields
excited on an electrically large dielectric-coated circular cylinder
is presented. The efficiency of the method results from the circumferentially
propagating representation of the Green’s function as
well as its efficient numerical evaluation along a steepest descent
path. The circumferentially propagating series representation of
the appropriate Green’s function is obtained from its radially
propagating counterpart via Watson’s transformation and then
the path of integration is deformed to the steepest descent path
on which the integrand decays most rapidly. Numerical results
are presented that indicate that the representations obtained here
are very efficient and valid even for arbitrary small separations
of the source and field points. This work is especially useful in the
moment-method analysis of conformal microstrip antennas where
the mutual coupling effects are important
Efficient analysis of input impedance and mutual coupling of microstrip antennas mounted on large coated cylinders
Cataloged from PDF version of article.An efficient and accurate hybrid method, based on
the combination of the method of moments (MoM) with a special
Green’s function in the space domain is presented to analyze antennas
and array elements conformal to electrically large material
coated circular cylinders. The efficiency and accuracy of the
method depend strongly on the computation of the Green’s function,
which is the kernel of the integral equation that is solved via
MoM for the unknown equivalent currents representing only the
antenna elements. Three types of space-domain Green’s function
representations are used, each accurate and computationally efficient
in a given region of space. Consequently, a computationally
optimized analysis tool for conformal microstrip antennas is obtained.
Input impedance of various microstrip antennas and mutual
coupling between two identical antennas are calculated and
compared with published results to assess the accuracy of this hybrid
method
Closed-Form Green's Function Representations in Cylindrically Stratified Media for Method of Moments Applications
Cataloged from PDF version of article.Closed-form Green's function (CFGF) representations for cylindrically stratified media, which can be used as the kernel of an electric field integral equation, are developed. The developed CFGF representations can safely be used in a method of moments solution procedure, as they are valid for almost all possible source and field points that lie on the same radial distance from the axis of the cylinder (such as the air-dielectric and dielectric-dielectric interfaces) including the axial line (ρ = ρ′ and φ = φ′), which has not been available before. In the course of obtaining these expressions, the conventional spectral domain Green's function representations are rewritten in a different form so that i) we can attack the axial line problem and ii) the method can handle electrically large cylinders. Available acceleration techniques that exist in the literature are implemented to perform the summation over the cylindrical eigenmodes efficiently. Lastly, the resulting expressions are transformed to the spatial domain using the discrete complex image method with the help of the generalized pencil of function method, where a modified two-level approach is used. Numerical results are presented in the form of mutual coupling between two current modes to assess the accuracy of the final spatial domain CFGF representations. © 2009 IEE
Analytic Expressions for the Ultimate Intrinsic Signal-to-Noise Ratio and Ultimate Intrinsic Specific Absorption Rate in MRI
Cataloged from PDF version of article.The ultimate intrinsic signal-to-noise ratio is the highest possible
signal-to-noise ratio, and the ultimate intrinsic specific
absorption rate provides the lowest limit of the specific absorption
rate for a given flip angle distribution. Analytic expressions
for ultimate intrinsic signal-to-noise ratio and ultimate intrinsic
specific absorption rate are obtained for arbitrary sample
geometries. These expressions are valid when the distance
between the point of interest and the sample surface is smaller
than the wavelength, and the sample is homogeneous. The
dependence on the sample permittivity, conductivity, temperature,
size, and the static magnetic field strength is given in
analytic form, which enables the easy evaluation of the change in
signal-to-noise ratio and specific absorption rate when the sample
is scaled in size or when any of its geometrical or electrical
parameters is altered. Furthermore, it is shown that signal-tonoise
ratio and specific absorption rate are independent of the
permeability of the sample. As a practical case and a solution
example, a uniform, circular cylindrically shaped sample is studied.
Magn Reson Med 66:846–858, 2011. © 2011 Wiley-Liss,
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