共查询到20条相似文献,搜索用时 46 毫秒
1.
A rigorous field theory method is described for the computer-aided design (CAD) of magnetically tunable E-plane metal-insert filters, where the waveguide sections are symmetrically loaded with ferrite slabs, and for large-gap finlines filters on a ferrite substrate. The design method is based on field expansion in suitably normalized eigenmodes which yields directly the modal scattering matrix of all discontinuities. The theory includes both higher-order mode interaction and the finite thickness of the metal inserts. Optimized data are given for magnetically tunable Ku-band metal insert and finline filter examples. The metal-insert type achieves a tuning range of its operating midband from about 14.1 to 15.7 GHz. The theory is verified by measurements 相似文献
2.
《Microwave Theory and Techniques》1968,16(10):835-842
The dispersion relations (/spl omega/-/spl beta/diagrams) for propagation of the quasi-TEM mode and higher-order symmetric modes in longitudinally magnetized ferrite-filled coaxial waveguide are presented. The dispersion relations for ferrite-filled coaxial cavity resonators are analyzed and presented graphically. The performance and operation of an X-band tunable ferrite filter is evaluated in light of the /spl omega/-/spl beta/diagrams 相似文献
3.
Three arrangements of the feeding structure for the excitation of a microstrip leaky wave antenna are proposed and investigated in this paper. A full-wave spectral domain integral equation method combined with the fundamental mode sampling technique is applied to determine the reflection coefficient of the excitation source. Tabulation technique is used to reduce the computational effort. Dependence on structural parameters such as line width, line spacing and overlap length is fully analyzed to obtain the design criteria for a microstrip leaky wave antenna. Additionally, an experimental setup is used to check the validity of our numerical results and verify the radiation nature of the microstrip line first higher-order mode 相似文献
4.
Poli F. Laegsgaard J. Passaro D. Cucinotta A. Selleri S. Broeng J. 《Lightwave Technology, Journal of》2009,27(22):4935-4942
A large mode area Yb-doped rod-type photonic crystal fiber design with a low refractive index ring in the core is proposed to provide an improved suppression of the first higher-order mode compared to the case of uniform core doping, in a way which is more robust against fluctuations in the refractive index value. After applying a scalar step-index model for a first parameter optimization of the proposed design, a full-vector modal solver based on the finite element method has been exploited to analyze the guided mode overlap and effective area for the most promising fibers identified. Finally, a spatial and spectral amplifier model has been considered to study the gain competition among the fundamental and the first higher-order mode guided in the Yb-doped rod-type fibers. Results have demonstrated the effectiveness of the low refractive index ring in suppressing the higher-order mode, thus providing an effectively single-mode behavior for the rod-type fibers. 相似文献
5.
Numerical analysis has been carried out for a waveguide with graded index and gain. It is shown that the radiation peak of the fundamental mode is deflected as the gradient of either the index or gain increases. The high-order modes also change their peak intensity ratio as the gradient of index or gain increases. The behavior of the fundamental mode is suitable for use in a beam scanner while that of higher-order modes is suitable for use in a deflection switching of laser beams. The analysis also shows that the modal gain of higher-order modes becomes larger than that of the fundamental mode as the gradient of the index and gain increases, which provides some explanation for the wide laser beam scanning observed by Scifres et al. 相似文献
6.
The pulse distortion due to energy reconversion from higher-order modes into the fundamental mode in randomly bent single-mode fibres is calculated. Pulse distortion can be reduced by either introducing mode filters or by a sufficiently large attenuation of the higher-order modes. Simple design considerations are given. 相似文献
7.
V. A. Kukushkin 《Semiconductors》2010,44(11):1435-1440
A scheme of a far-infrared and terahertz amplifier or laser based on a semiconductor nanostructure, consisting of a superlattice
of double quantum wells of a certain design placed into a planar metal waveguide and pumped by a CO2 laser, is suggested. The structure operation is based on the inversionless mechanism of electromagnetic field amplification,
which allows passing to room-temperature operation (in the pulsed mode) and significant (by a factor of more than 1.7) variation
in the output radiation frequency by simple variation in the pump intensity. A laser based on such a scheme can be a convenient
and easily tunable source of infrared and terahertz radiation for both basic research and various applications. 相似文献
8.
The dynamics of erbium-doped fiber ring lasers undergoing wavelength tuning is examined. The relaxation oscillations and mode build-up time are characterized. An all-optical damping technique which is capable of complete elimination of relaxation oscillations is analyzed, and measurements on a tunable erbium-doped fiber lasers are reported. An analytical solution is derived for the mode build-up time of tunable fiber lasers. Limiting parameters for the design of a high-speed tunable fiber laser are identified. An equalization technique for obtaining uniform switching speed is described 相似文献
9.
A TE11 mode emerging from the mouth of a conical horn excites higher-order modes, which can adversely affect the radiation pattern. This effect is substantially reduced over a 10% bandwidth by adding a series of resonant foam discs, which provide matching for the mouth and a filter passing only the desired mode over a suitable bandwidth. 相似文献
10.
The electromagnetic power coupling in asymmetrical double-groove guide is analyzed by finite element method (FEM) in this paper. The electrical field patterns of the dominant mode and the first higher-order TE mode have been presented. The electromagnetic field of the dominant mode is distributed with a concentration of energy in the wide groove region, while the electromagnetic field of the first higher-order TE mode is distributed with a concentration of energy in the narrow groove region. The results in this paper have important values in design of groove guide power coupler for millimeter wave applications. 相似文献
11.
The crosspolar radiation pattern of a corrugated waveguide is investigated theoretically and experimentally. It is shown that agreement can be obtained when the effects of space harmonics, the waveguide flange and a higher-order mode are included in the theory. 相似文献
12.
Yew Tai Chieng 《Photonics Technology Letters, IEEE》1996,8(2):212-214
An analytical expression for the mode build-up time of tunable fiber lasers is derived, based on a plane-wave lumped-circuit laser model and a two-level atomic system. Limiting parameters for the design of a high-speed tunable fiber laser can therefore be identified. 相似文献
13.
The electromagnetic power coupling in symmetrical and asymmetrical double circular-groove guides have been analyzed by finite element method (FEM) in this paper. The electrical field patterns of the dominant mode and the first higher-order TE mode have been presented. The electromagnetic field of the dominant mode distributes with a concentration in the two grooves and the region between grooves as well for symmetrical double circular-groove guide, while it distributes with a concentration in the groove with larger radius for the asymmetrical double circular-groove guide. The electrical field patterns of the first higher-order TE mode in symmetrical and asymmetrical double circular-groove guide are also presented. The figures in this paper have important values in design of circular-groove guide power coupler for millimeter wave applications. 相似文献
14.
The characteristics of higher-order modes of circular micro-strip antennas, such as radiation pattern, directivity, bandwidth, efficiency, and location of the feedpoint to match a 50?line, are studied, and the effects of varying the substrate parameters are investigated. A multifeed technique to generate any particular mode is also presented. 相似文献
15.
A double-element broad-band liquid crystal tunable filter consisting of a high-order quartz wave plate in series with a very-low-order electrooptically tunable liquid crystal phase plate and placed between crossed polarizers is described. A possible application for such a device is protection against intrusive laser radiation. The advantage of this double-element filter over a single-element low-order LC filter is that it increases the wavelength resolution of the device, which, when operated in the protect mode, allows continued sensing of the scene. Experimental and theoretical studies were made of the contrast ratios obtainable with such a filter 相似文献
16.
S. Sabchevski T. Idehara S. Mitsudo T. Fujiwara 《Journal of Infrared, Millimeter and Terahertz Waves》2005,26(9):1241-1264
In this paper we present some initial results from a conceptual design study focused on the development of a novel frequency tunable gyrotron for nuclear magnetic resonance (NMR) spectroscopy with signal enhancement based on the utilization of high field radiation and dynamic nuclear polarization (DNP) technique. The first variants of both the electron optical system and the resonant cavity which have been designed aiming continuous frequency tunability in a broad frequency band are presented and discussed. The selected method for frequency tunability is based on the excitation of higher order axial modes and smooth transition between them. It was selected after a critical examination of the known theoretical and practical results related to the frequency control in gyrotrons. It is believed that the current conceptual design is an appropriate basis for development of the next (optimized) design which will include also a detailed design of other components (mode converter, output window etc.) and magnetic circuit (superconducting magnet and supplementary solenoids) as well as for the overall mechanical design and fabrication of the prospective gyrotron. 相似文献
17.
Hole coupling in free electron lasers 总被引:1,自引:0,他引:1
Faatz B. Best R.W.B. Oepts D. van Amersfoort P.W. 《Quantum Electronics, IEEE Journal of》1993,29(7):2229-2238
Numerical simulations of the performance of a far-infrared free electron laser with an aperture in the upstream cavity mirror are presented. Two different applications of mirror apertures are studied: broadband extraction of radiation and injection of the electron beam. The emphasis is on the effect of the aperture on the amplitude of the higher-order transverse modes. It is shown that the mode distribution at saturation can be greatly influenced by variation of the mirror radius of curvature. A simple formula which is quite useful for predicting the dominant higher-order modes is derived. This permits optimization of the cavity with respect to the application in question 相似文献
18.
19.
Ao Sheng Rong Zhong Liang Sun 《Antennas and Propagation, IEEE Transactions on》1991,39(9):1366-1371
The radiation of millimeter waves from the nonradiative dielectric (NRD) leaky wave antennas with the tapered transition and the tuning aperture is investigated. An accurate theory for the leakage constant and the phase constant of the antennas is presented, which is based on the generalized scattering parameters considering the higher-order mode interactions at the discontinuities. The associated transverse equivalent network involves the characterization of the mode couplings at two air-to-dielectric interfaces, the coupled mode analysis of the tapered transition, and the calculation of the radiation fields at the tuning aperture via the extended spectral domain approach. The interesting behavior of the present modified configuration of NRD leaky wave antennas is illustrated by typical examples. The validity of the theory is confirmed by the comparison of the theoretical results with experimental data for the limiting cases 相似文献