Higher-Order Modes in Dielectrically Loaded Rectangular Waveguides

The problem of propagation in a waveguide containing E-plane slabs of dielectric was considered previously by several authors. However, their treatment was limited to the TE/sub mo/ modes. A more general and complete derivation of the dispersion equations for all the modes existing in these structures is presented here. It is shown, on the basis of theoretical and experimental results, that the frequency bandwidth is much smaller than the values previously obtained, considering only the TE/sub mo/ modes, for many cases of practical interest     

High-Power Microwave Rejection Filters Using Higher-Order Modes

In order to obtain filters capable of handling very high power, the use of radial lines and uniform line discontinuities was investigated. Forty-five-degree tapers and uniform lines were used to design a high-power microwave filter capable of handling 700 kw at 15 pounds pressure in a 0.900 by 0.400 ID waveguide. In addition to the filtering which results from the discontinuities in the TE/sub 10/ mode in the waveguide, high insertion loss elements are effected when the enlarged uniform line section is larger than the TE/sub 10/ mode waveguide wavelength and when the length of the enlarged section is approximately (2n -1)lambda/sub g//4. Extremely large insertion losses are possible by the cascading of these elements. Tuning, in the standard-size waveguide, has no effect on the insertion loss of the higher-mode enlarged waveguide at its resonant frequency. Empirical design formulas are evolved and the design procedure for band-rejection filters is given, using these high insertion loss elements.     

Resonant Frequencies of Higher-Order Modes in Radial Resonators

A summary of the relevant work on radial line discontinuities and radial line resonators is presented. A step-type discontinuity is analyzed using an integral equation formulation and the results are applied to the calculation of the resonant frequencies of a radial resonator. This method is verified by experiment and compared with the foreshortened-line approximation and with the methods of Marcuvitz and Goddard, whose work is satisfactory for the order TM mode. However, the present method is the only one which is equally applicable to the calculation of the resonant frequencies of TM modes possessing higher-order radial variations.     

Hybrid Modes in Circular Cylindrical Optical Fibers

The classification of hybrid modes in circular cylindrical optical fibers is studied. It is shown that problems of the mode classifications, i.e., the crossover of the dispersion characteristics and the remarkable changes of the polarization states and the field configurations, are caused by the coupling of the HE-type and EH-type modes.     

Magnetostatic Surface-Wave Transducers

Magnetostatic surface-wave (MSSW) transducer theory is extended and generalized. A Fourier transform relation is established between MSSW field amplitudes and transducer spatial current distribution. Expressions are developed for the radiation resistance of periodic meander and grating transducers, spatial harmonic amplitudes, and radiation resistance for uniform and nonuniform current distribution models. An expression is given for the radiation resistance of apodized transducers. The results enable one to predict transducer frequency response for a specified weighting of transducer element width, Iength and spacing.     

The Propagation Constants of Higher-Order Modes in Coaxial Waveguides With Finite Conductivity

Overmoded coaxial waveguides have been used in coaxial gyrotrons as a key interaction structure. To achieve the required mode selectivity, the resistivity of the center conductor is properly chosen to damp unwanted modes. Considering attenuation due to conductor loss, this study employs the perturbational method to determine the propagation constants of higher-order modes in the coaxial waveguide. The validity of the theoretical model is confirmed by comparison with results obtained using the high-frequency structure simulator (HFSS). Moreover, the method proposed herein is applied to analyze the ohmic mode selection of the coaxial waveguide.     

Suppression of Higher-Order Modes by Segmented Core Doping in Rod-Type Photonic Crystal Fibers

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.     

Eigenfrequency Shift of Higher-Order Modes in a Coaxial Cavity with Eccentric Inner Rod

The eigenvalues of a coaxial cavity must be modified by the structural eccentricity (for instance, by the misalignment of the inner rod), which causes an eigenfrequency shift. In this paper the eigenfrequency shift of the higher-order modes is numerically investigated in terms of the eigenvalue equation. Taking the TE_31, 17, 1, TE_32, 17, 1, TE_33, 17, 1 and TE_34, 17, 1 modes as examples, calculations show that the eigenfrequency of a mode may have a down-shift or up-shift, which depends on the ratio of the outer conductor radius to the inner rod radius R _out/R _in. For a higher-order mode, the greater the value of R _out/R _in, the smaller the influence of the structural eccentricity on the eigenfrequency shift. Moreover, the structural eccentricity may have a weaker influence if the azimuthal index of the mode is higher.     

Acoustic Surface-Wave Recirculating Memory

An acoustic surface-wave memory is described, operating at a bit rate of 220 MHz and storage capcity of 1280 bit-per recirculation loop. The transducers are coded using orthogonal pairs of Golay complementary sequences to obtain pulse-in pulse-out behavior. The shape of the delayed pulse is analyzed and compared with the pulse shape that is obtained using a simple single finger pair transducer. The recirculation electronics uses standard MECL-III logic for both the amplifier and the write, read, inhibit, and reclocking functions. The cost of the recirculating memory and the feasibility of constructing larger capacity stores are also discussed.     

Azimuthally Dependent Magnetostatic Modes In The Cylindrical Ferrites (Correspondence)

The azimuthally dependent magnetostatic modes have been investigated for two cases: 1) a hollow ferrite pipe is enclosed in a perfectly conducting wall; and 2) a ferrite rod is located at the center of a round waveguide, partially filling the cross section. Our analysis shows that the presence of the dielectric medium has an important role in the determination of the upper bound frequency and the cutoff wave number of the magnetostatic surface modes.     

Finite Element Analysis of the Field Patterns of Higher-Order TE and TM Modes in Rectangular-Groove Guide

The field patterns of the different TE and TM modes in a rectangular-groove guide are analysed by finite element method. The electric field, magnetic field and energy distributions in the groove guide for the dominant TE mode, the lowest TM mode and the 1st, 2nd, and 3rd higher-order TE,TM modes are presented. The results show that the low-loss characteristic of rectangular-groove guide seems unreliable. The results in this paper will be of benefit for us to understand the transmission characteristics of rectangular-groove guide, and will be of practical significance in designing groove guide components.     

圆柱弯曲型超声电机定子的结构优化

为满足圆柱弯曲型超声电机定子的结构设计要求和改善现有的设计方法,该文采用参数化设计语言ADPL自编制的优化设计程序对定子结构进行了优化,并制作出定子直径30 mm、长34 mm的圆柱弯曲型超声电机原型机.优化计算与实测结果表明,压电陶瓷片的中心位置十分接近于定子弯曲振型的波谷中心,定子驱动端与末端振幅比值的计算值与实测值基本吻合.     

岸-舰双基地地波超视距雷达技术

岸-舰双基地地波超视距雷达是一种在海边利用大型天线阵列发射、在舰船上接收的双基地多输入、单/多输出雷达。该雷达通过多个天线同时发射多个相互正交的信号,在接收端对各路发射信号分离后,利用发射阵列孔径通过信号处理综合形成发射方向图。概述该雷达的工作原理和主要特点,计算其威力覆盖范围,分析需要解决在运动平台上的时频同步、基于直达波的幅相校正、直达波抑制、电离层杂波与射频干扰的抑制等关键技术,介绍该雷达原理性试验系统及其试验结果。     

A Dielectric Surface-Wave Structure: The V-Line

Properties of the V-line, a wedge-shaped surface-wave structure comprising a cylindrical dielectric binding medium of sectorial cross section supported by two conducting plates, are considered in terms of its higher-order hybrid modes of propagation. Practical modifications of the ideal structure are emphasized. Design curves and equations are presented to determine various propagation parameters and their significance is discussed. Experimental verification of the theory is described.     

Nondegenerate Surface-Wave Mode Coupling Between Dielectric Waveguides

A new variational derivation of the coupling coefficient is given for the problem of nondegenerate surface-wave modes on parallel dielectric waveguides. The results coincide with those of a number of different methods in the literature on the degenerate case, but all give distinct results in the nondegenerate case. These differences are examined and compared with the exact solution, whereby the approximations involved can be evaluated for the case of two parallel slab waveguides.     

Linear Signal Processing by Acoustic Surface-Wave Transversal Filters

The impulse response of acoustic surface-wave (ASW) filters is determined by the configuration of an array of planar transducers tapping the acoustic signal propagated in the piezoelectric substrate. The transducer configuration is derived here by applying the generaI procedure used for the synthesis of linear transversal filters, which consists in time sampling the required impulse response and arranging the spacing and weights of the taps according to the time intervals and amplitudes of the impulse-response samples. The design of the tapping structure that synthesizes the impulse response of ASW transversal filters is based on a nonuniform sampling procedure, previously developed by the authors, that meets the particular requirements of ASW device operation. The features of this design procedure are presented, and several geometries of tapping transducers corresponding to impulse responses of different characteristics are discussed. The application of the procedure to the design of typical ASW filters is illustrated by the results of experimental models.     

Design of Unapodized Surface-Wave Transducers with Spectral Weighting

The technique commonly employed to provide a wide-band surface-wave transducer with a specific conversion loss as a function of frequency uses the linear frequency-modulation (LFM) (quadratic-phase) design. This provides the necessary dispersion, and anodization is then employed to obtain the required conversion loss. In some applications the anodization presents complications in that the beam generated has nonuniform width, and diffraction and phase-front problems can result. An alternate technique is described that relies on varying the number of effective transducer elements as a function of frequency to provide the conversion-loss variation. As examples of this technique, a flat bandpass filter for a nonlinear convolver and a very large fractional-bandwidth transducer (with spectral weighting to provide sidelobe control) for a memory application are described.     

Application of Acoustic Surface-Wave Technology to Spread Spectrum Communications

Spread spectrum transmission is being proposed for an increasing number of digital communication, navigation, and RADAR systems. One of the reasons is the simplicity and availability of surface-wave devices (SWD) for performing the necessary signal generation and processing. The properties of spread spectrum signals, the operation of SWD's, and their advantages and limitations when used in communication systems are discussed. Spread spectrum terminology and basic concepts are defined in terms common to both systems engineers and device designers.     

Analysis and Design of Dispersive Interdigital Surface-Wave Transducers

A comprehensive circuit model characterization of dispersive interdigital transducers with nonuniform electrode spacing is presented. The model is an extension of a three-port circuit which has been useful for representing periodic transducers. The extended model includes the effects of strong piezoelectric coupling whereby the acoustic waves and electric circuits interact, and it also accounts for reflections of acoustic waves which result from perturbations of the crystal surface by the metal electrodes. The inclusion of the latter effect is shown to be essential for explaining observed levels of triple-transit echos in filters and delay lines. The circuit model is used to derive a transducer design procedure which determines the electrode positions and the anodization function (acoustic aperture taper) required to reproduce a desired waveform. This procedure is applicable to the design of weighted dispersive filters and broad-band nondispersive delay lines. In order to verify the theory a low-loss octave-bandwidth nondispersive delay line was designed using linear FM dispersive transducers on YZ LiNbO/sub 3/. The performance of this device was found to be in good agreement with the circuit model predictions.