High Frequency Structure Simulator Software Research Articles

Estimation of complex permittivity of arbitrary shape and size dielectric samples using cavity measurement technique at microwave frequencies

In this paper, a simple cavity measurement technique is presented to estimate the complex permittivity of arbitrary shape and size dielectric samples. Measured shift in resonant frequency and change in quality factor due to the dielectric sample loading in the cavity is compared with simulated values obtained using the finite-element method software high frequency structure simulator and matched using the Newton-Raphson method to estimate the complex permittivity of a arbitrary shape and size dielectric sample. Complex permittivity of Teflon (PTFE) and an MgO-SiC composite is estimated in the S-band using this method for four different samples of varying size and shapes. The result for Teflon shows a good agreement with the previously published data, and for the MgO-SiC composite, the estimated real and imaginary parts of permittivity for four different shape and size samples are within 10%, proving the usefulness of the method. This method is particularly suitable for estimation of complex permittivity of high-loss materials

A novel broadband polarization diversity antenna using a cross-pair of folded dipoles

A /spl plusmn/45/spl deg/ polarization diversity antenna with wide bandwidth is presented in this letter. The antenna has a half-power beam width of 65/spl deg/ in the horizontal plane for use in wireless telecommunication base stations. Especially, a folded dipole antenna with a protruding part is used as a +45/spl deg/ polarization element and the another folded dipole with a concave part is used as a -45/spl deg/ polarization element. The protruding part and the concave part of dipoles make the two folded dipoles with the same height but not touching each other. With such a cross-pair of folded dipoles, a small polarization diversity antenna is constructed. The antenna was analyzed and optimized by the high frequency structure simulation software, and a good agreement was achieved between computation and experiments on the half-power beam width in the horizontal plane.

Digitalization decoupling method and its application to the phased array in MRI *

A general network decoupling method for phased array radio frequency coil used in magnetic resonance imaging is developed. A more flexible digital approach further simplifies the method, which has an even higher signal-to-noise ratio. The performance of the digitalized decoupling method was confirmed by the calculated result by using a high frequency structure simulation software with the method of finite element for a tree-port phased array RF coil. The consistence was well established between the theoretical and simulated results.

Theory of high-power wide-band traveling-wave tube using coaxial inverted helical groove slow-wave structure

A novel slow-wave structure (SWS), the coaxial inverted helical groove structure, is presented and those of its properties used for wide-band traveling-wave tube (TWT) are investigated. The first part of the paper concerns the wave properties of this structure in the case of a vacuum. The influence of the geometrical dimensions on dispersion characteristics and interaction impedance are investigated. The theoretical results reveal a very weak dispersion for the fundamental wave in the structure. The negative dispersion can be realized by a suitable selection of the structural parameters. The interaction impedance of the fundamental wave is about 10 /spl Omega/. The interaction impedance of the -1 space harmonic wave is much lower than that of the fundamental wave. Thus, the risk of backward wave oscillation is reduced. The software high frequency structure simulator (HFSS) is also used to calculate the dispersion property of the SWS. The simulation results from HFSS and the theoretical results agree well, which supports the theory. In the second part, a self-consistent linear theory of a coaxial inverted helical groove TWT is presented. The typical small signal gain per period is about 0.5 dB and the 3-dB small-signal gain bandwidth can exceed 25% with a 33-dB gain of tube.

A systematic optimum design of waveguide-to-microstrip transition

In this paper, a systematic optimum design method is introduced, which consists of the finite-element method (FEM), design sensitivity analysis (DSA), and the steepest descent algorithm. A waveguide-to-microstrip (W/G-to-M/S) probe-type transition is designed by using the proposed method. In the FEM as a full-wave analyzer, eigenvalue and eigenvector calculations in the two-dimensional (2-D) FEM precede the three-dimensional (3-D) FEM, in order to terminate the W/G-to-MIS transition model into an electrically small model. The analysis results of this approach are compared with ones of a commercial FEM software high-frequency structure simulator (HFSS). The total derivative required in the steepest descent algorithm is calculated numerically by the DSA based on the FEM. The additional time needed for this proposed method is only one more calculation of a sparse matrix equation. The return loss is chosen as the objective function to be minimized, and the backshort length and probe length are selected as the design variables in the transition design. The proposed method gives a good convergence characteristic and the optimized results show its usefulness.

Tractor-trailer crashes in Indiana: A case-control study of the role of truck configuration : E. R. Braver, P. L Zador, D. Thum, E. L. Mitter, H. M. Baum and F. J. Vilardo. Insurance Institute for Highway Safety, January 1994

Compositionally induced phase transitions in the system Sr(ZrxTi1−x)O3 were analyzed using a combination of X-ray diffraction, FT-Raman and FTIR spectroscopy. Sr(ZrxTi1−x)O3 system showed at least two tilting of phase transitions, pm3m–I4mcm and I4/mcm–pnma. The structural transition occurred due to tilting of BO6 octahedra. Dielectric constant measured with Hakki–Coleman technique decreased from 253 to 25 with increase of Zr content. The value of τf found 1771 ppm/°C for SrTiO3 which decreased to −82 ppm/°C for the SrZrO3. The dielectric resonator antenna (DRA) was investigated experimentally and numerically using a monopole antenna through an infinite ground plane and Ansoft's high frequency structure simulator software, respectively. The required resonance frequency and bandwidth of DRA were investigated in the composition between 0 ≤ x ≤ 1.0.