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1.
The output coupling of an idealized, symmetric model of a double-heterostructure (DH) laser is analyzed theoretically using parameters suitable to Pb1-x Snx Te. For the TEO mode incident at the laser mirror and for thin optical guiding regions such that only the TEO , TE1 , TMO , and TM1 modes may propagate, an exact formulation of the coupling problem is obtained including mode coupling at the mirror into the continuum of unguided radiation modes. Using this formulation, the power reflection and transmission coefficients, the fraction of incident power coupled into the radiation modes, the mirror illumination, and the far-field pattern are calculated for typical parameters. Significant mode coupling can occur, limiting the maximum external efficiency of such lasers. This and other potentially undesirable characteristics resulting from close optical confinement, such as large output beam divergence, must be considered in design criteria for DH structures in this alloy system. 相似文献
2.
The cross polarization from dual mode horn antennas supporting the TE11 and TM11 -modes has been analyzed both theoretically and experimentally. The cross polarization has been shown to be strongly dependent on the length and flare angle of the horn. When the flare angle for a given horn length becomes larger than a certain threshold angle, the cross-polar sidelobes increase rapidly. Simple formulas for this threshold angle are presented. This cross-polar degradation will not occur if a plane phase front is provided over the horn aperture, either by profiling the horn or by applying a lens in the aperture. 相似文献
3.
Burnside W. Pelton E. Peters L. Jr. 《Antennas and Propagation, IEEE Transactions on》1970,18(5):701-705
The radiation and phase scanning properties of a planar array are investigated using wedge diffraction theory. The TEM and TE01 radiation patterns are determined assuming that each guide is excited with equal amplitude but variable phase which is specified by the desired scan angle. Since the TE01 pattern can be used directly as theH -plane radiation pattern of an equivalent rectangular waveguide array, the analysis for this instance is extended to consideration of aperture reflection coefficients 相似文献
4.
The power-series expansion method has been used to compute the exact cutoff frequencies of TM modes in step-index fibers for various values of relative refractive index difference (Δ), ranging from 0.005 to 0.1. The difference between the propagation constants of TM and TE modes, intermodal delay between TM and TE modes, and their variation with respect to the relative refractive-index difference has also been calculated. Numerical results show that for a fiber withDelta = 0.005 the intermodal delay between TM01 and TE01 modes is of the order of 1.5 ps/km at frequencies far away from cutoff, whereas it is of the order of 0.62 ns/km forDelta = 0.1 . 相似文献
5.
An analytic model of diode lasers applicable to both the lasing and the nonlasing states is described. For these homogeneously broadened devices, spectral envelope widths for TE00 and TM00 modes are related to power in each modal family and are shown to depend critically on spontaneous emission coupling into the transverse modes. Thus, lasers with real-refractive index waveguiding (and associated weak spontaneous emission coupling) operate single longitudinal mode above threshold, whereas gain-guided devices run multimode. After connecting gain and spontaneous emission, a charge conservation equation, containing optical power in the form of a stimulated emission term, pumping current, spontaneous emission, and spectral width, is derived. These equations are then demonstrated to suffice for determination of the completeL versusI characteristic. For lasers in which both charge and mode confinement exist, such as the buried heterostructure (BH) and channelled-substrate narrow stripe (CNS) types, it is shown that both TM00 power and spectral envelope width approach limiting values at threshold, whereas TE00 mode power grows in conjunction with TE00 spectral envelope narrowing. 相似文献
6.
《Electron Devices, IEEE Transactions on》1961,8(5):381-386
Diode oscillations at frequencies between 1350 and 3700 Mc sometimes occurred in a particular high-voltage pulsed klystron. These frequencies agree closely with those calculated for an inverted spherical diode. The oscillations are often delayed a few microseconds after the electron beam is turned on. Experimental techniques revealed that two of the modes, TE41 and TE61 , with Q's of about 1000 had their highest electric fields in a region of the electron gun remote from the beam. 相似文献
7.
The TE and TM modes of anisotropic dielectric waveguides of crystal quartz have been studied in the far infrared using an optically pumped waveguide laser with a hybrid output mirror. Using Si and Ge prism couplers, excitation efficiencies of 56 percent of the theoretically calculated values were obtained for the TE0 mode. The measured propagation constants were found to agree closely with theory when the perturbation of the guided modes by the prism couplers was included. The attenuation constant for the TE0 mode atlambda_{0} = 496.1mu m was found to be as low asalpha_{TE_{0}} = 0.05 cm-1. A metal grating coupler for backward-wave coupling through a prism shaped TPX plastic substrate was also used to couple 89 percent of the guided energy in the TE0 mode out of the waveguide in the reverse direction. 相似文献
8.
The effect of dielectric loading upon theE -plane radiation patterns of rectangular horns is shown to give higher directivity with raised sidelobes. The main beam and first sidelobe can be predicted accurately in terms of radiation from aTM_{y10} mode. 相似文献
9.
The corrugated horn has been established as an antenna with low sidelobes and backlobes, rotationally symmetric patterns (for square pyramidal and conical horn shapes), and broad-band performance [1]-[9]. These properties make this horn useful for many applications. Previous studies have used conventional aperture integration techniques to evaluate the patterns of the corrugated horn. In general, the near axisE -plane radiation pattern of a pyramidal corrugated horn may be adequately predicted from standard analysis established for theH -plane patterns of conventional horn geometries [3]. This method, however, fails to predict the far-out sidelobe and backlobe radiation levels. The work presented here uses a knowledge of the aperture fields to predict the pattern using aperture integration and diffraction theory. The assumptions made concerning the aperture fields were verified by probing the internal fields and aperture fields of anX band corrugated horn. The results of this field probing are contained in the Appendix. The method of solution used in this paper parallels that used in previous publications [10]-[12]. Specifically, the pattern in the main beam region is computed using conventional aperture integration procedures, the contribution of theH -plane edges is found using a slope diffraction analysis, and the contribution of theE -plane edges is found by use of duality. 相似文献
10.
A simple dual-polarized feed horn that radiates fan-shaped primary patterns is described. The radiated patterns for the two orthogonal polarizations are essentially identical and are suitable for illuminating cut paraboloidal reflectors withf/D ratios of about 0.3. The horn is similar to conventional flared waveguide feed horns except that the corners have been modified to yield an octagonally shaped aperture. The horn has the added advantage of suppressedE -plane sidelobes, thus reducing spillover radiation. 相似文献
11.
A unified formulation of the optimization of monopulse antenna performance indices for a specified sidelobe envelope function and/or specified nulls of the pattern is presented. The performance indices considered are beam efficiency, gain factor, and angular sensitivity factor of rectangular and circular apertures. The unconstrained optimization of beam efficiency result in an integral equation, the solutions of which are prolate spheroidal wave functions for rectangular aperture and hyperspheroidal wave functions for circular aperture. These functions reduce, respectively, to Legendre and Zernike polynomials in the case of gain factor and angular sensitivity factor. The double orthogonality properties of these eigenfunctions are used for constrained optimization. The results obtained by this technique for the near-in sidelobes constrained at a uniform level are shown to be in agreement with the earlier works. The method is applicable for other aperture surfaces such as elliptical, ellipsoidal, and spherical. 相似文献
12.
13.
Gallium arsenide has been investigated as a waveguide-cladding material for use as a cutoff polarizer for integrated optics. Calculations show that a 20 nm thick film of GaAs can be used to select either the TM0 mode or both TM0 and TE0 modes, while maintaining a guide attenuation of less than 100 cm-1. 相似文献
14.
针对小口径低剖面天线的多频段、低旁瓣和高效率的需求,提出一种基于切割赋形环焦天线和非均匀有理B样条(non-uniform rational B-spline,NURBS)曲面的环焦型椭圆波束天线的综合优化设计方法.该方法首先采用样条函数将一维口面场参数化,针对赋形切割环焦天线进行第一次快速优化设计;然后,用NURBS曲面将优化后的天线主副反射面再次参数化,引入多目标优化差分进化算法,以天线效率和第一旁瓣为优化目标,对该环焦型椭圆波束天线进行第二次优化设计.应用该方法设计并加工了一个410 mm×720 mm的环焦椭圆波束天线,工作频率覆盖了Ku/K/Ka三个频段,天线总效率达到49%以上,第一旁瓣低于–14 dB,电压驻波比小于1.44∶1.实测结果和全波仿真结果吻合良好,验证了本文设计方法的有效性. 相似文献
15.
A dual polarized aperture coupled circular patch antenna using a C-shaped coupling slot 总被引:1,自引:0,他引:1
Padhi S.K. Karmakar N.C. Sr. Law C.L. Aditya S. Sr. 《Antennas and Propagation, IEEE Transactions on》2003,51(12):3295-3298
The design and development of a dual linearly polarized aperture coupled circular microstrip patch antenna at C-band are presented. The antenna uses a novel configuration of symmetric and asymmetric coupling slots. Variations in isolation between orthogonal feedlines and antenna axial ratio with the position of coupling slots are studied and broadband isolation and axial ratio are achieved. The prototype antenna yields 7.6 dBi peak gain, 70/spl deg/ 3-dB beam width, 25 dB cross-polarization levels and an isolation better than 28 dB between the two ports. With an external quadrature hybrid coupler connected to the two orthogonal feedlines, the antenna yields 3-dB axial ratio bandwidth of more than 30% at 5.8 GHz. 相似文献
16.
Bumman Kim Chen Tsai 《Quantum Electronics, IEEE Journal of》1979,15(7):642-647
Theoretical and experimental studies of optical filtering which utilize anisotropic and noncollinear acoustooptic interaction in aY -cut LiNbO3 waveguide are reported. A guided-light beam from either an He-Ne laser at 6328 Å or an argon laser at around 5000 Å, propagating at an angle centering around 70° from theZ(c) axis of the LiNbO3 crystal, was Bragg diffracted by the surface acoustic wave with 500 MHz center frequency and propagating at 16° from thex axis of the crystal. High optical resolving power, large optical angular aperture, and good spatial separation between the filtered light and the unfiltered light have been simultaneously achieved. An optical passband of 16 Å and an angular aperture of 9° have been measured for the case in which the undiffracted and diffracted light propagate in TE0 mode and TM0 mode, respectively. Furthermore, by varying the acoustic frequency from 350 to 670 MHz, the filtered optical wavelength may be tuned from 8300 to 5000 Å. 相似文献
17.
《Electron Devices, IEEE Transactions on》1981,28(7):872-875
Initial tests of a fast-millimeter-wave wide-band gyrotron traveling-wave amplifier (gyro-TWA)of novel design have demonstrated a small-signal 3-dB bandwidth of 13 percent with 18-dB gain at midband (35 GHz)using a 70-kV 1-A annular electron beam. This reflection-type amplifier using the TE01 circular-electric mode has a linear tapered Waveguide circuit with an axial magnetic field profiled to maintain synchronism. 相似文献
18.
Input impedance and bandwidth of an annular ring microstrip antenna have been determined by modeling the antenna as a section of radial line loaded with wall admittances. The effect of mutual coupling between the radiating apertures has been taken into account. The theoretically calculated values of input impedance for TM12 -mode are compared with measurements. The agreement is good. Higher order modes have been found to be present in the vicinity of TM12 -mode. The reactance due to these modes can be utilized to increase the voltage standing-wave ratio (VSWR) bandwidth of the antenna. 相似文献
19.
C. E. Tong R. Blundell M. Carter 《Journal of Infrared, Millimeter and Terahertz Waves》1989,10(9):1153-1163
A simple E-plane tapered rectangular dielectric rod fed by NRD guide is used as a millimeter wave antenna. This class of aerial features attractive radiation patterns with relatively low sidelobes and moderate gain. The measured results show that such an antenna and mounting structure can be exploited as effective radiating element in the short millimeter wave frequency band. 相似文献
20.
C. E. Tong R. Blundell M. C. Carter 《Journal of Infrared, Millimeter and Terahertz Waves》1989,10(10):1327-1337
A simple E-plane tapered rectangular dielectric rod fed by NRD guide is used as a millimeter wave antenna. This class of aerial features attractive radiation patterns with relatively low sidelobes and moderate gain. The measured results show that such an antenna and mounting structure can be exploited as effective radiating element in the short millimeter wave frequency band. 相似文献