Browsing by Author "Chen, KC"

Now showing 1 - 8 of 8

A circuit-modeling perspective of leaky-mode leakages in a corner-fed square patch
(2002-08-01)
Chen, KC
;
Tzuang, CKC
;
電信工程研究所
;
Institute of Communications Engineering
This paper chronicles the leaky-mode leakages in a corner-fed square patch. First, the measured peak RPA (relative power absorbed, 1 - S-11(2) - S-21(2)) values of the two-port corner-fed square patch (two-port test circuit) are reported. These are 21.1%, 52.3%, 89.8% and 81.3% at 5.68 GHz, 11.76 GHz, 16.68 GHz and 22.29 GHz, respectively. Such periodicity of frequencies and the phenomenon of increasing losses at higher frequencies enable us to link these peak frequencies to leaky-mode excitations. The modal spectra of the higher-order leaky modes with a strip width of 630 mil, equal to the side length of the square patch, are obtained by the well-known space-domain integral equation method. The maximum available power gain (G(A,max)), obtained by simultaneously complex conjugate matched impedance at the referenced two ports of the test circuit, depicts that (1) nearly loss-free transmission parameter outside the leaky-mode regions and (2) substantial losses inside the leaky-mode regions. This result suggests that the leaky modes are the main sources causing losses for the two-port test circuit. Furthermore, the valley points of the measured and theoretical G(A,max) are about -7.5 dB, -9.7 dB and -12.0 dB at 10.13 GHz, 16.68 GHz and 22.29 GHz, respectively, and all are in the leaky-mode regions of the modal spectra. The one-port properties of the two-port patch with the second port opened are then investigated. The degenerated (0, N) and (N, 0) modes (N = 1, 2, 3 and 4), calculated by the cavity model method, fall into the strong leakage regions from the first to the fourth higher-order leaky modes. The well-known leaky line's frequency-scanning characteristics also appear in the one-port test circuit, with the angle of the main beam moving from theta = 30degrees to theta = 40degrees as the operating frequency is increased from 22.50 GHz to 23.75 GHz. Lastly, a two-dimensional (2-D) transmission-line model of the one-port test circuit is proposed. This model uses two orthogonal modal currents as excitations to stimulate the corner-fed square patch. At 22.60 GHz, in the fourth higher-order leaky mode (EH4) region, the current distributions obtained by the 2-D transmission-line model closely agree with those of the full-wave simulation. This consistency shows that the damped-oscillation current distributions of the corner-fed square patch at 22.60 GHz are caused significantly by the multiple reflections of the leaky mode. Furthermore, at the resonant frequencies of the patch, the tangled bound-mode resonance of the EH0 mode can enhance the leaky-mode leakages.
A divide-and-conquer-based algorithm for automatic simulation vector generation
(2004-03-01)
Yen, CC
;
Jou, JY
;
Chen, KC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A periodic microstrip radial antenna array with a conical beam
(2003-04-01)
Chen, KC
;
Qian, YX
;
Tzuang, CKC
;
Itoh, T
;
電信工程研究所
The analysis and design of a microstrip antenna array with a conical beam are presented. The antenna array employs a periodic structure derived from the microstrip on a perforated ground plane. The microstrip antenna array consists of eight leaky lines evenly distributed around a circle. Each line radiates mainly a pair of forward and backward beams, forming a conical beam. The new leaky line design employs the concept of space-harmonic modulation on the EH0 mode launched at the common joint of the antenna array. The scattering and dispersion characteristics of the leaky line are thoroughly investigated. The fact that the perturbation of the antisymmetric holes made by photolithographic etching excites the leaky EH1 mode is theoretically and experimentally validated. Scattering analyses of the surface currents on the microstrip, however, reveal in detail the physical operation of the leaky line. The dispersion characteristics are, thus, established and shown in a Brillouin diagram, indicating the role of each space harmonic, denoted by its complex propagation constant gamma(m,n)(+/-). gamma(m,n)(+/-) represents a traveling-wave component of the nth higher-order spatial component in association with the EHm mode: the superscript, + signifies a forward (backward) traveling wave. For the particular leaky line design, gamma(0)(+),(-1) and gamma(1,0)(+) space barmonics, both showing odd-symmetric field polarization, and both outside the triangular Brillouin region, form the backward and forward leaky waves, respectively. When the leaky lines are evenly and collinearly tied, an 11.5-GHz radial antenna array prototype is formed, and emits a conical beam, showing a 3-dB beamwidth of 24degrees at the flare angle of 31degrees.
Elastic interaction between screw dislocations and a circular surface crack
(1997-03-31)
Lin, KM
;
Lin, HC
;
Chen, KC
;
Chang, HL
;
材料科學與工程學系
The behaviour of a screw dislocation around a circular surface crack was analyzed using the conformal mapping method. The effects of the crack length l and its radius of curvature R on the shielding effect and the strain energy were discussed in detail. It was found that for a dislocation being fixed at a constant distance from the crack tip and located on a plane tangent to crack surface at the tip, there exists a critical crack length l* corresponding to a maximum shielding effect induced by the dislocation on the circular surface crack. The l* increases with R and approaches infinity as the crack becomes planar (i.e. R --> infinity). The shielding effect vanishes as the crack disappears. It increases rapidly with l if 0 < l much less than l*, regardless of R. After reaching the maximum, it decreases slightly for larger R but significantly for smaller R as the crack becomes longer. The shielding is more pronounced for larger R than that for smaller R, with the difference increasing with crack length. As a result, a surface microcrack propagates initially in a rather brittle manner then becomes more ductile. When the crack gets longer, it still keeps ductile for a less curved or a planar crack but becomes relatively brittle for a severely curved crack. In addition, the strain energy is also significantly influenced by crack length and increases rapidly with l when l is rather small, regardless of R. With increasing l, it becomes less affected by l, and the variation with R is still not obvious, with larger R corresponding to a slightly higher strain energy. (C) 1997 Elsevier Science S.A.
Elastic interaction between screw dislocations and a circular surface crack
(1997-03-31)
Lin, KM
;
Lin, HC
;
Chen, KC
;
Chang, HL
;
材料科學與工程學系
The behaviour of a screw dislocation around a circular surface crack was analyzed using the conformal mapping method. The effects of the crack length l and its radius of curvature R on the shielding effect and the strain energy were discussed in detail. It was found that for a dislocation being fixed at a constant distance from the crack tip and located on a plane tangent to crack surface at the tip, there exists a critical crack length l* corresponding to a maximum shielding effect induced by the dislocation on the circular surface crack. The l* increases with R and approaches infinity as the crack becomes planar (i.e. R --> infinity). The shielding effect vanishes as the crack disappears. It increases rapidly with l if 0 < l much less than l*, regardless of R. After reaching the maximum, it decreases slightly for larger R but significantly for smaller R as the crack becomes longer. The shielding is more pronounced for larger R than that for smaller R, with the difference increasing with crack length. As a result, a surface microcrack propagates initially in a rather brittle manner then becomes more ductile. When the crack gets longer, it still keeps ductile for a less curved or a planar crack but becomes relatively brittle for a severely curved crack. In addition, the strain energy is also significantly influenced by crack length and increases rapidly with l when l is rather small, regardless of R. With increasing l, it becomes less affected by l, and the variation with R is still not obvious, with larger R corresponding to a slightly higher strain energy. (C) 1997 Elsevier Science S.A.
Leaky properties of microstrip above a perforated ground plane
(1999)
Chen, KC
;
Tzuang, CKC
;
Qian, YX
;
Itoh, T
;
電信工程研究所
A leaky line is proposed. The leaky line emits leaky wave by feeding the bound mode that is not supposed to leak. The proposed guiding structure consists of a microstrip above a perforated ground plane with etched holes positioned anti-symmetrically. A prototype is built and tested to verify the concept. The two-port scattering parameters of the leaky line employing the well-known full-wave integral equation method agree well with the measured data. The investigation of RPA (relative power absorbed) and G(A,max) (maximum available power gain) of the prototype points to a substantial excitation of the EH1 leaky mode, over 50% leakage of input energy for the 72 mm long prototype at 6.5 GHz.
Leaky-modes leakage from planar circuits
(1997)
Chen, KC
;
Tzuang, CKC
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
Inherent leakages in certain two-dimensional planar circuits are related to the propagation of leaky modes, contrasting to the conventional awareness of the association of leaky modes with the uniform waveguides. Both theoretical and experimental studies confirm the newly found phenomena exist in proximity-coupled or direct-fed two-dimensional planar circuits of irregular shapes. Hence the leaky modes are indispensable when designing a microwave planar circuit.
Low temperature growth of carbon nanotubes on printing electrodes by MPCVD
(2006-03-01)
Chen, KC
;
Chen, CF
;
Chiang, JS
;
Hwang, CL
;
Chang, YY
In this work, combination of screen-printing process and microwave plasma enhanced chemical vapor deposition system (MPCVD) was applied to fabricate patterned carbon nanotubes (CNTs) on the cathode electrodes on glass substrates. Solution based Ni catalyst was well-mixed with Ag powders and organic binder materials to forin screen printed paste. CNTs were then grown under the atmosphere Of CH4/H-2 gas mixture below 550 degrees C. In the field emission measurement, the tum-on field was 3.2 V/mu m and uniform electron emission image was also observed. (c) 2005 Elsevier B.V. All rights reserved.