Mode conversion in the resonance region of parallel plate magnetoplasma waveguides

Nonreciprocal propagation in parallel plate, magnetoplasma waveguide is restricted to transverse magnetic (TM) modes when the waveguide cross-section is nonsymmetrical. The analysis of this canonical structure is extended here by including collision frequency loss in the characteristic equation and by studying mode propagation in the extraordinary wave resonance region. Conversion between the dominant and first higher order mode is observed as the bias field is increased through resonance. Field plots are included to illustrate this effect.     

Wideband microwave filter constructed by asymmetrical compact microstrip resonator and floating plate coupling structure

The realisation of a microwave filter is presented by using the asymmetrical compact microstrip resonator and floating plate coupling structures. The filter demonstrates the properties of low insertion loss, wide pass bandwidth and two controllable transmission zeros, which results in fast roll-off responses near to the corner frequencies of the passband. It also has the advantages of compact size, ease of fabrication and absence of via holes. An X-band prototype with 34% fractional bandwidth was designed and fabricated to verify the proposed design concept. Good agreement between simulation and measurement was obtained.     

Compact superconducting dual-log spiral resonator with high Q-factor and low power dependence

A new dual-log spiral geometry is proposed for microstrip resonators, offering substantial advantages in performance and size reduction at subgigahertz frequencies when realized in superconducting materials. The spiral is logarithmic in line spacing and width such that the width of the spiral line increases smoothly with the increase of the current density, reaching its maximum where the current density is maximum (in its center for /spl lambda//2 resonators). Preliminary results of such a logarithmic ten-turn (2 /spl times/ 5 turns) spiral, realized with double-sided YBCO thin film, showed a Q.-factor seven times higher than that of a single ten-turn uniform spiral made of YBCO thin film and 64 times higher than a copper counterpart. The insertion loss of the YBCO dual log-spiral has a high degree of independence of the input power in comparison with a uniform Archimedian spiral, increasing by only 2.5% for a 30-dBm increase of the input power, compared with nearly 31% for the uniform spiral. A simple approximate method, developed for prediction of the resonant frequency of the new resonators, shows a good agreement with the test results.     

大孔耦合输出的虚共焦非稳腔的研究

本文提出了一种新颖的、应用于高功率激光器的复合谐振腔——大孔耦合输出的虚共焦非稳腔。对这种腔的设计作了细致的分析,并给出设计方法。同时对该腔的激光模式进行了理论和实验研究,理论和实验结果相吻合。输出的最大激光功率为750w,相应的光电转换效率为8.0％,输出激光的远场发散角为1.73mrad。     

矩形金属机壳孔缝电磁耦合特性研究

针对矩形金属机壳上孔缝在高功率电磁环境下的电磁耦合问题,提出了一种使用模式匹配法和基于矩量法求解的混合位积分方程来分析孔缝电磁耦合特性的全波混合算法.该算法考虑了高次模、孔缝形状、孔缝厚度以及入射波极化方向等因素对电磁耦合特性的影响.通过将数值仿真结果与经典孔缝电磁耦合模型的测试结果进行对比,验证了该算法具有较高的准确性,与经典的时域有限差分法相比,该算法具有很高的计算效率.研究结果表明:有孔金属机壳在外界强电磁辐射条件下具有明显的谐振效应,在谐振频率点,耦合进入机壳的电场将大大增强,且孔缝附近以及机壳中心的耦合电场峰值要高于其他位置的耦合电场峰值;随着机壳表面上孔缝厚度的增加,耦合进入其内部的电场也在减弱;当机壳上的孔缝为矩形且入射波的电场极化方向平行于矩形缝隙的短边时,对应于该极化方向的孔缝电场耦合强度是所有极化方向中最强的.     

Simplified equivalent circuit for a piezoelectric resonator with high electromechanical coupling

A simplified equivalent circuit, which has been used for a resonator with low electromechanical coupling is still a good approximation for a high coupling resonator, provided that the parallel capacitance is so chosen that the circuit yields the exact antiresonance frequency. All the circuit constants can be experimentally determined.     

Adaptive synthesis and design of resonator filters with source/load-multiresonator coupling

The paper presents a universal and comprehensive synthesis technique of coupled resonator filters with source/load-multiresonator coupling. The approach is based on repeated analyses of a circuit with the desired topology; no similarity transformation is needed. Restrictions imposed by the implementation on the coupling coefficients such as signs and orders of magnitudes are straightforwardly handled within this technique. The technique is then used to synthesize and design filters with full or almost full coupling matrices by selecting, among the infinite number of solutions, the matrix that corresponds to the actual implementation. In such cases, analytical techniques and those based on similarity transformations cannot be used since they provide no mechanism to constrain individual coupling coefficients in order to discriminate between two full coupling matrices, which are both solutions to the synthesis problem. Using the technique described in this paper, a filter designer can extract the coupling matrix of a filter of arbitrary order and topology while enforcing relevant constraints. There is no need to master all the different existing similarity-transformation-based techniques and the topologies to which they are applicable. For the first time, detailed investigations of parasitic coupling effects, for either compensation or utilization, are made possible. The method is applied to the synthesis of a variety of filters, some of which are then designed and built and their response measured.     

A compact fir ring laser with open resonator and variable output coupling

We describe the design, construction and first experimental results with an open triangle FIR ring resonator with Michelson interferometer output coupling, which we combined with a Brewster-windowless 10W CO₂ pump laser to a compact laser package of 1m length. The achieved stability of power and frequency of this system is very high, typically on the order of ±0.01% over several hours and <20kHz per hour at 800GHz. For the design, we investigated the balance of all laser processes and determined the optimum dimensions for the open resonator cavity. This analysis is based on a radially homogenous overall laser model, including commonly accepted simplified rate equations together with molecular parameters for weak FIR laser lines. In accordance with the modelling the efficiency on the very most prominent lines is better than with conventional waveguide lasers, giving up to ≈4 times better efficiencies especially on lines with low absorption pump transitions. Several laser lines, however, have substantially enhanced pump thresholds on purely copropagating emission, suppressing laser operation below about 10W pump power threshold. We show that this can not be due to effects from the interferometer.     

Mode coupling in tapered structures

The theory of strong mode coupling involving nonorthogonal modes is extended to tapered structures. Initially, an attempt is made to show that previous formulations of the problem of nonorthogonal-mode coupling in tapered structures are incomplete. An equation is derived which is the generalization to tapered structures of the coupled-mode formalism with nonorthogonal modes     

Compact dual-mode elliptic-function bandpass filter using a singlering resonator with one coupling gap

A novel microwave dual-mode elliptic-function bandpass filter with one coupling gap structure is proposed. This filter has a 4.7% bandwidth at 1.805 GHz with 1.73 dB insertion loss. The filter provides less field perturbation of the ring resonator than conventional filters. Without the output coupling gap between the feed line and the ring resonator, a low insertion loss has been obtained. This compact, high performance filter is useful for mobile and personal communication systems     

The evolution of quenches in superconducting parallel bifilarwinding by fault current

A superconducting parallel bifilar winding with one strand in each branch was tested and analyzed. When quenched by a fault current, it showed the so-called “fast quench” and the experimental results explained the increase of resistance. Also the experiments confirm that the current redistribution of magnetically coupled strands develops new normal zones after the initial quench, and that the size of normal zones at an early stage increases almost linearly as dI/dt increases. By these results, we could explain the resistance rise of the superconducting parallel bifilar winding when quenched by a current above the critical value     

Mode coupling in spiral fibre gratings

The coupling properties of spiral fibre gratings are presented. It is shown that LP₀₁ modes in spiral fibre gratings couple to both LP₁₁ even and odd modes     

Mode coupling in coaxial waveguides with varying-radius center andouter conductors

The mode conversion process in a coaxial waveguide with varying-radius center and outer conductors is shown to be described by a system of first-order differential equations-the coupled mode equations. The nondiagonal coefficients of this system are called the coupling coefficients. In this paper, we derive the explicit expressions for the coupling coefficients in a varying-radius coaxial waveguide and discuss some of their important features. These coefficients can be used in determining model conversion in a coaxial cavity with slowly varying walls or designing and analyzing coaxial waveguide tapers and mode converters. Some experimental results of the coupling coefficients for the case of azimuthally symmetric modes, TE_0n modes, are also given     

A novel electromagnetic bandgap metal plate for parallel plate modesuppression in shielded structures

A novel type of metal plate structure incorporated with electromagnetic bandgap holes for use as metal shields with the capability of suppressing the propagation of unwanted parallel plate mode has been proposed. The holes can be of any shape and the periods of those holes should be selected to half the guided wavelength of the parallel plate mode at a desired center frequency of suppression. To show the validity of the proposal, inert electromagnetic wave simulation, results of a shielded microstrip structure designed for application in the 76 GHz frequency band are demonstrated. Experiments are performed with a prototype designed in the 10 GHz frequency band and parallel plate mode suppression is verified successfully with the excellent agreement between experimental and simulation results     

Mode coupling in optical waveguide horns

Mode coupling in optical waveguide horns is described in detail. Analytic approximations for the coupling constant and phase difference are derived. For a parabolic-shaped horn an expression for the power transferred out of the lowest order mode is obtained, which demonstrates that long structures will be needed to maintain adiabatic operation.     

Mode coupling loss in single-mode fibers with depressed inner cladding

Single-mode fibers with depressed inner cladding show sharp resonant loss peaks near the fundamental mode cutoff wavelength where the core-guided mode starts to become a leaky mode. The magnitude of the loss peak exceeds 200 dB/km and was found to be extremely sensitive to fiber curvature. The phenomenon is attritubed to mode coupling between the core-guided mode and the discrete modes guided in the outer cladding.     

Equivalent circuit for multiple vias in parallel plate environment

An equivalent one-dimensional circuit has been developed to model the loading effects of vias (through or buried) in a parallel plate environment. Owing to the one-dimensional nature of the model, the simulation time is dramatically reduced, compared to either two-dimensional inductance-capacitance ladder network or full-wave numerical electromagnetic simulations. This model can be easily included in available commercial circuit simulators and accounts for multiple via interactions as well as for substrate edge reflections     

Numerical and experimental analysis of the field to enclosure coupling in reverberation chamber and comparison with anechoic chamber

This paper presents a study of coupling between an external field and a metallic enclosure with a long aperture in the frequency range which includes several box resonances. A reverberation chamber (RC) and an anechoic chamber (AC) are considered as a field generation structure. In both cases, a customized FDTD code is used to calculate the current induced by the external field in a loop placed inside the enclosure. In order to simulate the AC facility, a single plane wave is used to represent the test field, whereas for the RC, the field is represented by a proper superposition of random plane waves. Numerical results are experimentally validated. The proposed method is useful to investigate the performance of the enclosure during its early design stage before the realization of a prototype.