The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Lin-kun Wu - One of the best experts on this subject based on the ideXlab platform.
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Side Lobe Suppression of a Short Leaky-Wave Antenna by Phase Constant Tapering: Analysis and Design
IEEE Transactions on Antennas and Propagation, 2015Co-Authors: Jeng-hau Lu, Jie-huang Huang, Lin-kun WuAbstract:Uniform leaky-wave antennas (LWAs) with limited length have suffered from the presence of high-level side lobes, which could lead to the reception of unwanted noise especially when the LWA is short. This communication examines how the Phase Constant of a short LWA can be manipulated to achieve side lobe suppression. The tapering of the Phase Constant is shown to result in higher order “image patterns,” which can be used advantageously for side lobe suppression. Validation of this principle is given by a cosine-shaped width-tapering profile design of a half-mode substrate-integrated waveguide (HMSIW) LWA. The measured results show that the side lobe level (SLL) of a short (1.4 λ0) HMSIW LWA has been suppressed to below -16 dB in the entire space wave leakage region using this tapering profile.
K.j. Webb - One of the best experts on this subject based on the ideXlab platform.
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A study of slotline leaky-wave antennas
IEEE Transactions on Antennas and Propagation, 1990Co-Authors: G.w. Slade, L. Carin, Q. Xu, S.e. Borchardt, K.j. WebbAbstract:The results of an experimental investigation of several millimeter-wave slotline leaky-wave antennas at 94 GHz are given. The experimental results show how variations in the transverse slot geometry affect the radiation pattern. Additionally, slot geometry variations also change the polarization performance of the antenna. The narrow transverse slot array was more sensitive to a perpendicularly (E/sub y/-E/sub z/) polarized electric field than the wide slot case. Also, the change in the effective Phase Constant along the antenna with changing slot dimensions caused a noticeable shift in the angle of the main beams. However, the beamwidths for all cases remained about the same. A simple model is presented to explain this. For designing an antenna of this form, the effective Phase Constant, beta , can be approximately determined using a numerical analysis of the uniform slot problem. Given beta and the operating frequency and the scanning ranges, the element spacing can be determined. The attenuation Constant does not change much when the transverse slot widths are varied. If greater sensitivity to an E/sub y/-E/sub z/ polarized wave is desired, the transverse slots should be narrow.
Jose Luis Gomez-tornero - One of the best experts on this subject based on the ideXlab platform.
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A simple technique for the dispersion analysis of fabry-perot cavity leaky-wave antennas
IEEE Transactions on Antennas and Propagation, 2012Co-Authors: Carolina Mateo-segura, Maria Garcia Vigueras, Alexandros P. Feresidis, George Goussetis, Jose Luis Gomez-torneroAbstract:A simple analysis technique to extract the complex dispersion characteristics of thin periodic 2-D Fabry-Pérot leaky wave antennas (LWA) is presented. The analysis is based on a two-stage process that dispenses with the need for root-finding in the complex plane. Firstly, full-wave MoM together with reciprocity is employed for the estimation of the LWA radiation patterns at different frequencies from which the Phase Constant is calculated. Employing array theory the Phase Constant is subsequently used to estimate the radiation patterns for different values of the leakage rate. The correct value for the leakage rate is identified by matching the corresponding radiation pattern to that obtained using the full-wave method. To demonstrate this technique, we present results for half-wavelength and sub-wavelength profile LWAs. Unlike the transverse equivalent network method, the proposed technique maintains its accuracy even for antennas with low profile.
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Efficient dispersion analysis of 2-D high-gain Leaky-Wave Antennas
Proceedings of the Fourth European Conference on Antennas and Propagation, 2010Co-Authors: Carolina Mateo-segura, Maria Garcia Vigueras, George Goussetis, Jose Luis Gomez-tornero, Alexandros P. FeresidisAbstract:A new simple and rigorous analysis technique is presented to derive the complex dispersion characteristics of periodic 2-D Fabry-Pérot Leaky-Wave Antennas (LWA). In order to illustrate the basics of the method an example involving a 2-D periodic array acting as a partially reflecting surface (PRS) situated at half-wavelength distance from a ground plane is utilised. The analysis procedure is based on a combination of array theory and periodic method of moments (MoM) yielding a fast and accurate calculation of the complex propagation Constant of the leaky-mode of interest. Full-wave MoM together with reciprocity is employed for the estimation of the LWA radiation patterns at different frequencies from which the Phase Constant is determined. Subsequently, employing array theory the Phase Constant as calculated by MoM is used to estimate the radiation patterns. The leakage rate is obtained by simple matching of the resulting radiation patterns to those obtained using full-wave MoM. The technique is applicable to antennas with sub-wavelength profile where other techniques such as transverse equivalent network (TEN) lose accuracy.
G. Chu - One of the best experts on this subject based on the ideXlab platform.
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Bifurcation behavior of wind energy generation systems
2nd International Symposium on Power Electronics for Distributed Generation Systems PEDG 2010, 2010Co-Authors: Zhengxi Li, S C Wong, Chi K. Tse, G. ChuAbstract:Use of the doubly fed induction generator (DFIG) in wind energy generation systems allows variable speed operation by using partially rated back-to-back PWMconverters. Although many control schemes have been reported in the literature to address some specific control problems, few has considered the general stability of the entire system. Specifically, bifurcation analysis of the system has not been reported so far. Lowfrequency oscillation has been found in a practical power grid system with the wind farm being connected to single-Phase Constant power loads. In this paper, the rotor speed of the DFIG is used as a variation parameter for bifurcation analysis. Bifurcation diagram of the voltage link capacitor clearly indicates the instability phenomenon of the practical DFIG system in supersynchronous operation when unbalanced single-Phase Constant power loads are connected to the connecting grid. © 2010 IEEE.
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Bifurcation in wind energy generation systems
International Journal of Bifurcation and Chaos, 2010Co-Authors: Zhengxi Li, S C Wong, Chi K. Tse, G. ChuAbstract:This letter reveals the possibility of Hopf bifurcation in a grid-connected wind energy generation system which handles an unbalanced loading. The wind energy generation system consists of a typical doubly fed induction generator (DFIG) which allows variable speed operation by using partially rated back-to-back quadruple active and reactive power PWM converters. Many control schemes reported in the literature are designed to solve some specific control problems associated with DFIG and have rarely been tested for general stability. Specifically, bifurcation analysis of the system has not been reported so far. We study the system stability in terms of the magnitude of some unwanted oscillation of the voltage link capacitor under a practical scenario where the system interacts indirectly with unbalanced single-Phase Constant power loads through the power grid. In this letter, the rotor speed of the DFIG is used as a variation parameter for bifurcation analysis. Bifurcation diagram of the voltage link capacitor indicates a Hopf-like bifurcation of the system in super-synchronous operation. This clearly explains the instability phenomenon of the practical DFIG system when unbalanced single-Phase Constant power loads are connected to the connecting grid. © 2010 World Scientific Publishing Company.
Jeng-hau Lu - One of the best experts on this subject based on the ideXlab platform.
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Side Lobe Suppression of a Short Leaky-Wave Antenna by Phase Constant Tapering: Analysis and Design
IEEE Transactions on Antennas and Propagation, 2015Co-Authors: Jeng-hau Lu, Jie-huang Huang, Lin-kun WuAbstract:Uniform leaky-wave antennas (LWAs) with limited length have suffered from the presence of high-level side lobes, which could lead to the reception of unwanted noise especially when the LWA is short. This communication examines how the Phase Constant of a short LWA can be manipulated to achieve side lobe suppression. The tapering of the Phase Constant is shown to result in higher order “image patterns,” which can be used advantageously for side lobe suppression. Validation of this principle is given by a cosine-shaped width-tapering profile design of a half-mode substrate-integrated waveguide (HMSIW) LWA. The measured results show that the side lobe level (SLL) of a short (1.4 λ0) HMSIW LWA has been suppressed to below -16 dB in the entire space wave leakage region using this tapering profile.