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Broad Bandwidth (broad + bandwidth)
Selected AbstractsModeling and optimization of cylindrical antennas using the mode-expansion method and genetic algorithmsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 6 2005Dawei Shen Abstract For monopole antennas with cylindrically symmetric structures, a mode-expansion method is highly time efficient, which is a realistic approach for integrating function-optimization tools, such as genetic algorithms (GAs), in order to extract the best bandwidth property. In this article, a mode-expansion method is used to simulate the impedance characteristics of the cylindrical antennas. As examples, two new types of monopole antennas are presented, one of which possesses a two-step top-hat structure while the other has an annulus around the stem. After the modeling scheme is examined for convergence and data validity, the associated optimization problem, with dimensions as decision variables, structural limitations as linear constraints, and desired bandwidth performance as an objective function, is solved using GAs. The effects of the geometric parameters on the impedance characteristics are investigated in order to demonstrate the optimality of the calculated solutions. Two optimized practical antennas are designed based on our numerical studies. One has a broad bandwidth of 3 GHz while the other shows a dual-band property, which can satisfy the bandwidth requirements for both Bluetooth (2.45-GHz band) and WLAN (5-GHz band) systems. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. [source] Dynamical diffraction of ultrashort X-ray free-electron laser pulsesJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2001S. D. Shastri Calculations are presented for the femtosecond time-evolution of intensities of beams diffracted by perfect Bragg crystals illuminated with radiation expected from X-ray free-electron lasers (XFELs) operating through the self-amplified spontaneous emission (SASE) process. After examining the case of transient diffraction of an electromagnetic delta-function impulse through flat, single- and double-crystal monochromators, the propagation of a 280,fs-duration SASE XFEL pulse of 8,keV photons through the same optics is discussed. The alteration of the sub-femtosecond spiky microbunched temporal structure of the XFEL pulse after it passes through the system is shown for both low-order (broad bandwidth) and high-order (narrow bandwidth) crystal reflections. Finally, the shot-to-shot statistical fluctuations of the integrated diffracted intensity is simulated. Implications of these results for XFEL applications are addressed. [source] An X-band microstrip oscillator integrated with frequency-selecting patch antennaMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2009D. H. Lee Abstract A simple design for microstrip oscillator consisting of an active source and an output patch antenna is presented. The active source is designed to possess negative-resistance over broad bandwidth but not to oscillate without the output patch antenna. Two different source circuits that are potentially unstable over full C-band and X-band are fabricated. Six different-size patch antennas are then connected with each source circuit to demonstrate the oscillation frequency control. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1963,1966, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24481 [source] Broadband gap-coupled half hexagonal microstrip antennasMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2008K. P. Ray Abstract Three configurations of compact gap-coupled half hexagonal microstrip antennas have been presented for broad bandwidth. Parametric studies for the effect of coupling gap and feed point location on the performance of these antennas have been investigated and the results have been validated experimentally. Increase in bandwidth is more than twice for the two configurations and about four times for the third case when compared with that of the corresponding hexagonal microstrip antenna. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 271,275, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23069 [source] A broadband microstrip Marchand balun with vertical coupling structureMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2007Hee Nam Abstract In this paper, a broadband microstrip Marchand balun is presented. It is implemented by new vertical coupled structure, which is suggested to improve the coupling effect in the conventional coupler. Using this vertical coupling structure, the Marchand balun shows broad bandwidth of larger than 115% at the center frequency of 2.3 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 752,755, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22281 [source] Design and double negative property verification of C band left-handed metamaterialMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2006Fan-Yi Meng Abstract In this article, a left-handed (LH) metamaterial with miniaturized unit cell and broad bandwidth is designed. Its relative bandwidth is 56.4%, and the unit cell electrical size is 0.067 at the central frequency where the LH metamaterial is available. The effective permittivity and effective permeability are extracted from the transmission and reflection data at normal incidence for the LH metamaterial proposed here. The double negative (DNG) property is shown by the simultaneously negative effective permittivity and effective permeability and is confirmed by the equivalent circuit. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1732,1736, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21763 [source] Negative permeability around 630 nm in nanofabricated vertical meander metamaterialsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2007Heinz Schweizer Abstract We demonstrate a new design of a 3-dimensional meander structure that exhibits negative permeability with a broad bandwidth between 550 nm and 665 nm. The structural design allows for full coupling of the magnetic field component at all angles of incidence. We compare our structure with other metamaterial structures with respect to the series capacitance contributions of the different metamaterials. The investigation of optical metamaterials is carried out combining transmission line analysis with numerical simulations of Maxwell's equations. The analysis is demonstrated for typical split ring structures and the novel 3D meander metamaterial structures. Comparing the resulting scattering parameter spectra as well as the retrieved effective material parameters, we find that transmission line description remains valid for metamaterials at optical frequencies. We find in addition that the longitudinal capacitance is the decisive parameter to achieve negative permeability with a broad bandwidth at optical frequencies. For experimental verification we manufactured split-ring resonator structures and meander metamaterial structures with linewidths down to 30 nm, element sizes down to 100 nm, and periods between 200 nm and 350 nm. For meander metamaterial structures a permeability value of ,1 was achieved within a bandwidth of 50 nm centered at 630 nm. The largest absolute value of ,4.5 was achieved at 650 nm. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||