Browsing by Author "WU, LK"

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A COMPUTATIONALLY EFFICIENT METHOD OF EVALUATING GREENS-FUNCTIONS FOR 1-D, 2-D, AND 3-D ENCLOSURES
(1989-07-01)
DEMAREST, KR
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MILLER, EK
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KALBASI, K
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WU, LK
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交大名義發表
ANALYSIS OF DISPERSION AND SERIES GAP DISCONTINUITY IN SHIELDED SUSPENDED STRIPLINES WITH SUBSTRATE MOUNTING GROOVES
(1992-02-01)
WU, LK
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CHANG, HM
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交大名義發表
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傳播研究所
;
National Chiao Tung University
Dispersion and series gap discontinuity of shielded suspended striplines (SSL's) on Duroid substrate (epsilon(r) = 2.22) are analyzed using the finite-difference time-domain method (FD-TD). Numerical accuracy of better than 0.15% is achieved when the FD-TD is used to calculate the effective dielectric constant (epsilon(reff)) of an air-filled rectangular coaxial transmission line. Data obtained for the frequency-dependent epsilon(reff) of uniform SSL's, and both scattering and equivalent circuit parameters of various series gap discontinuities, are then presented. In general, presence of sidewall mounting grooves causes a nearly frequency-independent small reduction in epsilon(reff). On the other hand, proximity effects of the housing are found to be more important. It is demonstrated that: 1) for a given housing, epsilon(reff) decreases first with an increase in strip width before increasing again when strip is wider enough to interact strongly with the sidewalls and 2) reducing sidewall spacing causes an increase in epsilon(reff). For the gap discontinuity, coupling across the gap is stronger for wider strips and/or narrower gap width. Irregular transmission behavior is also found when strip is wide enough to interact strongly with the sidewalls.
ANALYSIS OF THE EFFECTS OF A RESISTIVELY COATED UPPER DIELECTRIC LAYER ON THE PROPAGATION CHARACTERISTICS OF HYBRID MODES IN A WAVE-GUIDE-SHIELDED MICROSTRIP USING THE METHOD OF LINES
(1993-08-01)
CHUNG, SJ
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WU, LK
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交大名義發表
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傳播研究所
;
National Chiao Tung University
In this paper, propagation characteristics of even-symmetric hybrid modes in a waveguide-shielded microstrip in the presence of a resistively coated dielectric layer affixed to the top cover of the housing is analyzed with the method of lines. The resistive boundary condition is employed to model the resistive film. A shielded microstrip line having a unity strip-width-to-substrate-thickness ratio (i.e., w/h1 = 1) placed on top of a 0.635-mm-thick alumina substrate is considered. Based on a 10h1 x 7h1 reference housing, four different housing arrangements are obtained by varying the structural parameters of the resistively coated dielectric layer. Results obtained indicate that the effects of both the housing walls and the resistively coated upper dielectric layer on the dominant (quasi-TEM) mode are insignificant and may be ignored when frequency is above 15 GHz. For the higher order modes, resistive film appears to be transparent when film resistance is greater than about 1 kOMEGA, it behaves as a good conductor when film resistance is much smaller than 100 OMEGA, and in between it results in nonlinear (and even oscillatory) higher order modal behaviors. Apparently, due to the increasing field concentration inside the upper dielectric (as suggested by the increasing epsilon(reff)) for a given mode, both the maximum attenuation and the film resistance needed to achieve it increase with frequency and dielectric constant of the upper dielectric layer.
CHARACTERIZATION OF THE SHIELDING EFFECTS ON THE FREQUENCY-DEPENDENT EFFECTIVE DIELECTRIC-CONSTANT OF A WAVE-GUIDE-SHIELDED MICROSTRIP USING THE FINITE-DIFFERENCE TIME-DOMAIN METHOD
(1991-10-01)
WU, LK
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CHANG, YC
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交大名義發表
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傳播研究所
;
National Chiao Tung University
The dispersion behavior of waveguide-shielded microstrip line is investigated using the finite-difference time-domain method. The result is a frequency-dependent effective dielectric constant. Structures having centered strip are examined to determine the effects of a top cover alone and the effects of two symmetrically placed sidewalls. Structures with off-centered strip are used to investigate the effects of a single sidewall alone and the combined effects of a single sidewall plus the top wall. Differences between the effects of a single sidewall alone and those of the two symmetrically placed sidewalls are identified. In addition, new results on the combined effects of the top wall plus one sidewall, which are important when considering the placement of the outermost elements of a packaged circuit, are also discussed.
E-POLARIZED SCATTERING FROM A CONDUCTING RECTANGULAR CYLINDER WITH AN INFINITE AXIAL SLOT FILLED BY A RESISTIVELY COATED DIELECTRIC STRIP
(1992-06-01)
WU, LK
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HAN, LT
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交大名義發表
;
傳播研究所
;
National Chiao Tung University
The potential use of resistive films for damping the resonance spikes observed in the radar cross section (RCS) spectrum of a partially open rectangular cavity is investigated using a recently developed finite-difference time-domain (FDTD) method that utilizes the resistive sheet boundary condition for the modeling of resistive films. Backscattering data obtained in the first resonant region for an E-polarized plane wave normally incident into the slotted side of the cavity are presented. It is shown that resonance behaviors can be eliminated completely with a low-resistance film (e.g., R(S) = 188.5-OMEGA) which attenuates significantly the impinging wave. Poorer resonance damping performance is observed as the film resistance increases to 754-OMEGA because more of the field is allowed to penetrate into the cavity. For the latter case, the presence of the resistive film lowers the Q-factor of the slotted cavity such thal the resultant resonance spectrum is lower in strength and broader in bandwidth.
EFFECTS OF A RESISTIVELY COATED DIELECTRIC STRIP ON THE TM-POLARIZED RESONANT BACKSCATTER BEHAVIOR OF A SLOTTED CONDUCTING RECTANGULAR SHELL
(1993-06-01)
WU, LK
;
LU, CH
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交大名義發表
;
傳播研究所
;
National Chiao Tung University
The performance of a resistively coated dielectric strip used to suppress the first TM-type resonant backscatter associated with a two-dimensional slotted conducting rectangular shell is analyzed in this paper using the moment method technique. Results obtained indicate that almost perfect resonance damping performances are attained when a finite-dimensioned resistively coated dielectric strip with dielectric constant epsilon(r) = 4-j0.4 and film resistance R(s) = 188.5 OMEGA is placed: (1) at the sw (which directly faces the normally incident TM-polarized plane wave), (2) on the interior perimeter of the shell adjacent to the slot, or (3) at the center of the back wall of the shell. Poorer damping performances are observed, however, when the resistively coated dielectric strip is placed at other positions and/or with the same or higher film Finally, ft is also shown that in general the knowledge of the waveguide theory can be used advantageously in the placement of the resistively coated dielectric strip for achieving best resonance damping performance.
FDTD ANALYSIS OF THE RADIOMETRIC TEMPERATURE-MEASUREMENT OF A BILAYERED BIOLOGICAL TISSUE USING A BODY-CONTACTING WAVE-GUIDE PROBE
(1995-07-01)
WU, LK
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NIEH, WK
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交大名義發表
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電信工程研究所
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National Chiao Tung University
Radiometric signal received by an open-ended rectangular waveguide probe in direct contact with a bilayered biological tissue is analyzed by the FDTD method. Two-layer tissue model consists of an outer thin skin layer over a semiinfinite fat layer is analyzed for a X-band total power radiometer. A spherical tumor with same permittivity as, but slightly higher temperature than, the surrounding normal fat tissue is assumed to exist inside the fat tissue. Active probe characteristics are analyzed first using the FDTD method for a propagating, sinusoidally time-varying, TE(10) type of excitation source. For the same waveguide probe operated as the radiometer antenna, radiometric weighting factors associated with individual tissue cells are then derived from the FDTD calculated field values, Near field radiating characteristics of the probe and radiometric signals determined for tumors of various size and depth are discussed, Presence of the skin is found to result in lower power transmission coefficient across the probe aperture and significantly lower absorbed powers by fat; both of these contribute to much lower radiometric signals observed.
IMPLEMENTATION AND APPLICATION OF RESISTIVE SHEET BOUNDARY-CONDITION IN THE FINITE-DIFFERENCE TIME-DOMAIN METHOD
(1992-06-01)
WU, LK
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HAN, LT
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交大名義發表
;
傳播研究所
;
National Chiao Tung University
Use of resistive sheet boundary condition in the finite-difference time-domain (FDTD) analysis of scattering problems involving resistively coated dielectric object is described. The algorithm is introduced through an analysis of E-polarized scattering from a thin resistive strip. For the sheet resistance R = eta-Z0/2 with Z0 being the intrinsic impedance of vacuum, numerical experiments indicate that algorithm stability is ensured in all cases if delta-t is chosen according to c-eta-delta-t less-than-or-equal-to delta. Validity of the resultant FDTD method is verified in a comparison of computed E-polarized scattering data for several resistive strips with existing data. New results on the E-polarized scattering behavior of resistively coated dielectric strip as a function of surface resistances and angle of incidence are also presented. Finally, extension to the H-polarized case and application of the present method to pulsed problems are briefly discussed.