Propagation of infrared radiation in hollow microstructuralcylindrical waveguides

Theoretical and numerical results are presented on the propagation of infrared radiation in TE₀₁-, TM₀₁-, and TE₁₁-like modes in an empty cylindrical, gold-coated waveguide of micron dimensions. Low-loss propagation is possible for the TE₀₁-like mode, whose configuration is similar to that of the TE₀₁ mode in a guide with perfectly conducting walls. Propagation is more lossy for the TM₀₁- and TE₁₁-like modes. While for small guide radii these modes resemble the TM₀₁ and TE₁₁ modes in a guide with perfectly conducting walls, they transform into surface waves as the guide radius is increased, with losses that are independent of guide radius     

Broadband linearly polarized beat-wave TEm1/TE11 mode converters

Broadband linearly polarized waveguide mode converters have been developed to transform the high-order cylindrical TE_m1 output wave from harmonic gyrotron amplifiers into the more useful TE₁₁ fundamental waveguide mode. The converter's corrugation period is equal to the beat between the two waves and the bandwidth is predicted to be inversely proportional to the number of periods. Four-period TE ₃₁/TE₁₁ and TE₄₁/TE₁₁ converters with an azimuthal perturbation of m_c=4 and m_c =5, respectively, have yielded a peak conversion efficiency of 98% with a bandwidth greater than 3% and a one-period beat-wave converter has been designed to yield 12% bandwidth. However, it has been observed in measurements that the strong coupling in a short converter can lead to a shift of the center-frequency with an accompanying reduction of the efficiency and bandwidth. A two-period TE₄₁/TE₁₁ converter with 5% bandwidth displayed a 5% frequency shift and a conversion efficiency of only 86%     

一种适用于波束扫描的宽带低剖面介质谐振器天线

近年来,为解决传统介质谐振器天线（dielectric resonator antenna, DRA）体积庞大等问题,新颖的低剖面DRA如介质贴片天线和平面介质天线被提出并迅速成为研究热点. 然而,现有的低剖面DRA设计要么平面尺寸较大（>0.5λ₀×0.5λ₀）,要么带宽较窄（<10%）,限制了它们的实际应用. 文中提出了一种具有小型化平面尺寸的宽带低剖面DRA. 本天线采用介质贴片设计,顶部为高介电常数的介质贴片,中间为低介电常数的介质基板,底部为缝隙馈电结构. 缝隙馈电结构可激励起介质贴片谐振器的基模TE₁₁₁和高次模TE₁₃₁两种工作模式,这两种模式的场分布在贴片边缘部分存在基模场强较弱而高次模场强较强的显著区别. 本设计巧妙地利用了该区域的模式场强区别,通过略微增加贴片边缘部分高度来显著影响高次模谐振频率而轻微影响基模谐振频率,从而将高次模TE₁₃₁的谐振频率迅速下拉并与基模TE₁₁₁的谐振频率靠近合并,在不增大介质贴片平面尺寸的前提条件下获得宽带工作效果. 本天线的三维尺寸为0.35λ₀×0.35λ₀×0.08λ₀ (λ₀为中心频率处的空气中波长),线极化实物案例测试结果表明该天线具有18.5%的?10 dB阻抗带宽以及7.3 dBi的最大增益. 该天线平面尺寸小,适用于具有波束扫描功能的阵列天线设计;且提出的设计理念还可进一步拓展应用于圆极化天线设计.     

Novel Microwave Network for the Leaky-Wave Analysis of Evanescent Fields in Stub-Loaded Structures

In this paper, a new transverse equivalent network for the modal analysis of stub-loaded leaky-wave antennas is developed. The derived network is useful for the study of the radiation of evanescent fields that occurs when they reach the top aperture of the parallel-plate stub. This transverse network is based, for the first time, on a nonhybrid formulation of the constituent parallel-plates modes of order 1 (TE₁ ^Z and TE₁ ^Z ). The obtained network is an alternative to the one based on hybrid TE₁ ^Vand TE₁ ^V modes, and leads to a simpler transverse resonance equation. The new equivalent network is validated by obtaining leaky-mode dispersion curves for a previously studied leaky-wave antenna in non- radiative dielectric guide technology.     

Improving the symmetry of radiation patterns for offset reflectorsilluminated by matched feeds

The large difference between the dominant sidelobe levels in the asymmetric and symmetric plane radiation patterns of the short-focal-length offset paraboloids is minimized by illuminating the reflector with a prime-focus tilted matched feed. The amplitude of the asymmetric mode (TE₂₁) component in the matched feed is numerically evaluated for achieving an optimum peak cross-polar level. Effect of the feed tilt on the reflector efficiency is also indicated     

Propagation of lower-order modes in a radially anisotropiccylindrical waveguide with liquid crystal cladding

The propagation behavior of the four lower-order modes, HE₁₁ , TE₀₁, TM₀₁, and HE₂₁, in a radially anisotropic cylindrical waveguide with liquid crystal cladding is studied both theoretically and experimentally. The cylindrical waveguide is a doubly-clad fiber with an isotropic core and inner cladding and a radially anisotropic outer cladding made of nematic liquid crystal. Theoretically, the propagation and decay constants for the TE₀₁ and TM₀₁ modes are obtained by solving the wave equations exactly, while those for the HE₁₁ and HE ₂₁ modes are derived using perturbation techniques under the weakly guiding approximation. It is predicted that in such a structure the guided TE₀₁ mode can be separated from the leaky HE₁₁, TM₀₁, and HE₂₁ modes. The theoretical results show good agreement with the experimental observations for a 3 cm long fiber cell with a 5 μm inner cladding radius     

Theory and experiment of a coaxial probe fed hemisphericaldielectric resonator antenna

A hemispherical dielectric resonator antenna fed by a coaxial probe is studied both theoretically and experimentally. The Green's function for the evaluation of the input impedance is derived rigorously and expressed in a form convenient for numerical computations. The method of moments is used to obtain the probe current from which the input impedance of the DR antenna is calculated. Both delta gap and magnetic frill source models are considered. Moreover, the results using a reduced kernel as well as the exact kernel are presented. Both entire basis (EB) and piecewise sinusoidal (PWS) expansion modes are used and the results are compared. The effects of the probe length, feed position, and dielectric constant on the input impedance are discussed. Finally, the theoretical radiation patterns for the first three resonant modes (TE₁₁₁, TM₁₀₁, and TE₂₂₁) of the DR antenna are presented     

Compact quasi-periodic and aperiodic TE0n modeconverters in overmoded circular waveguides for use with gyrotrons

Designs of compact quasi-periodic and aperiodic TE_0n-TE _0n-1 circular waveguide converters for use with gyrotrons in an electron cyclotron heating (ECH) system are developed by analytically and numerically solving the coupled-mode differential equations. Quasi-periodic mode transducer designs which convert the TE₀₂ mode to the TE₀₁ mode, and in some cases also include a taper (waveguide radius reduction), are developed. A 60-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE₀₂-TE₀₁ mode converter. A 140-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE₀₃-TE₀₂-TE₀₁ mode converter. The resulting designs are highly efficient (conversion efficiencies ⩾99.4%), are shorter, have a broader bandwidth than previous designs, and have a waveguide radius greater than or equal to 1.389 cm over the entire length of the transducer to allow for high-power transmission. Experimental results consistent with theoretical calculations are presented     

Design and analysis of a coaxial coupler for a 35-GHz gyroklystronamplifier

A single rectangular TE₁₀ feed four-slot coaxial coupler is designed and built for excitation of a TE₀₁₁ cylindrical cavity mode for use in high-power millimeter-wavelength gyroklystron amplifiers. A high degree of mode purity is obtained and matching of the cavity to the input line is studied. A model based on the mode-matching technique and dipole radiators has been formulated to predict operation of this coupler. The resulting numerical code is capable of finding resonant frequency and cavity bandwidth in a small fraction of the time taken by more general finite-difference/finite-element design tools. The model can be extended to self-consistently include an electron beam, and the model is compared to a coupler design based on Hewlett-Packard's High-Frequency Structure Simulator code. The coupler has been successfully used in a high-power gyroklystron-amplifier experiment     

双/三模基片集成波导和共面波导混合结构滤波器设计

针对微波带通滤波器小型化、高性能的应用需求,提出使用双/三模方形基片集成波导和共面波导混合结构设计带通滤波器.通过改变双模基片集成波导中TE₁₀₂和TE₂₀₁的谐振频率和外部耦合的强弱,可实现具有近似椭圆、非对称和无传输零点响应的双模滤波器;两个相同尺寸的共面波导作为谐振器蚀刻在基片集成波导表面,与TE₁₀₂和TE₂₀₁共同形成一个通带,设计具有多样性响应的四阶滤波器.在具有非对称响应四阶滤波器的基础上,使主模TE₁₀₁频率移动到该通带附近,设计更宽带宽的五阶滤波器.并对设计的滤波器进行加工和测试.测试结果与仿真结果吻合,表明了该混合结构设计高性能滤波器方法的可行性.     

The design of serpentine-mode converters for high-power microwaveapplications

In this paper, we report the design methodology and numerical results for two mode converters that are suitable for high-power microwave applications. Both converters are designed to operate at 11.424 GHz and utilize periodic serpentine structures to convert between modes with different azimuthal-mode indexes. The first converts about 98.5% of an incident linearly polarized TE₁₂ mode to the TE ₀₁ mode when oriented as an H-plane bend, but has just 1% mode conversion to all modes when oriented as an E-plane bend. The second device converts a linearly polarized TE₁₁ mode to a TM ₀₁ mode with over 99.99% effectiveness. The performance of both devices with respect to parametric variations is detailed. Experimental measurements of the radiation patterns from the TE₁₂ -to-TE₀₁-mode converter are consistent with the theoretical predictions     

A quasi-optical mode converter with a bifocal mirror

This paper presents the design procedure of a quasi-optical mode converter to transform any kind of TE_mn mode into a Gaussian wave beam and experimental results obtained in the particular case of the TE₆₄ mode at 110 GHz. The quasi-optical system consists of a helical-cut launcher and a bifocal mirror, which is designed, using the techniques of geometric optics, to focus the radiation of the launcher into a Gaussian focal spot. Such a system was fabricated and tested for the transformation of the TE₆₄ mode. The experimental results showed that about 80% of the power incident in the focal plane is focused into a small Gaussian-like spot of less than 20 mm diameter, while 97% of the power is contained into the main TE₆₄ lobe     

光子晶体双波长电光调制和模分复用集成器件

为了实现光电子器件小型化和多功能化,进一步提高信息传输容量和速度,提出了一种基于光子晶体双波长电光调制和模分复用的片上集成器件。该集成器件的电光调制模块由硅基光子晶体波导和两个L3型复合腔组成,模分复用模块由硅基非对称平行纳米线波导组成,两个模块的连接处采用硅基光子晶体波导。采用L3型复合腔和PN掺杂结构实现两个波长TE₀模的调制,采用非对称定向耦合结构将两个波长的TE₀模转换为TE₁模。应用基于三维时域有限差分法（3D-Finite Difference Time Domain,3D-FDTD）的Lumerical软件进行仿真分析,结果表明,在调制电压为1.05 V时,该集成器件可以实现中心波长为1 552.1 nm和1 556.1 nm的 TE₀模、TE₁模通断调制及两模式模分复用功能。该器件的消光比高达24.67 dB,调制深度均为0.99,插入损耗小于0.57 dB,信道串扰小于?34.68 dB,调制速率最低为17.54 GHz。该集成器件结构紧凑,可望应用于高速大容量光通信系统。     

A composite optical waveguide-based polarimetric interferometer forchemical and biological sensing applications

A new polarimetric interferometer has been developed on the basis of the phase difference between transverse electric (TE)₀ and transverse magnetic (TM)₀ modes in a composite optical waveguide (OWG). The composite OWG consists of a single-mode potassium ion-exchanged planar waveguide overlaid with a high-index thin film that has two tapered ends and supports only the TE₀ mode. Applying tapered velocity coupling theory, we found that the TE₀ and TM₀ modes coexisting in the potassium ion-exchanged layer were separated in the thin film region of the composite OWG: the TE₀ mode was coupled into the thin film while the TM₀ mode was confined in the potassium ion-exchanged layer. Interference occurs between TE- and TM-polarized output components when a single output beam is passed through a 45°-polarized analyzer. The phase difference φ between both orthogonal output components is very sensitive to the superstrate index n_c in the thin film region. Our experimental results indicate that a slight change of Δn_c=3.71×10^-6 results in the phase-difference variation of Δφ=1° for a 5-mm-long TiO ₂/K⁺ composite OWG with a 34-nm-thick TiO₂ film. Such a simple polarimetric interferometer can be applied to chemical or biological sensors by modifying the upper film surface of the composite OWG with a chemically or biologically active substance     

Fast frequency-step-tunable high-power gyrotron withhybrid-magnet-system

The TE_22,6 1 MW gyrotron operated at Forschungszentrum Karlsruhe (FZK) at frequencies between 114 and 166 GHz has been investigated with respect to the fast-frequency tunability in the frequency range from 132 to 147 GHz. For that purpose, the gyrotron has been equipped with a special hybrid-magnet system consisting of superconducting (sc) magnets in the cryostat and additional normal conducting (nc) copper magnets with a fast time constant. Some special problems due to the magnetic coupling between the different magnets were investigated by calculation and experiment. Making use of these investigations some different current regulation systems for the nc magnets were implemented and tested experimentally. Finally a step-tuning operation between the modes from TE_20,6 to TE_24,6 in time steps of 1 s has been achieved     

Design of triple mode TE01δ resonator transmissionfilters

The use of triple mode TE_01δ cubic resonators for the design of transmission mode filters is presented. Frequency tuning and coupling between modes are studied experimentally. The tunability of all inter-cavity couplings, necessary for the realization of a wide range of transfer functions, is demonstrated with a 6th degree, 5 MHz wide filter at 2 GHz. With an insertion loss of 0.7 dB in a volume of 260 cm³, the filter presents a 2:1 volume reduction over conventional TE_01δ filters     

FDTD simulation of radiation characteristics of half-volume HEM and TE-mode dielectric resonator antennas

Cylindrical and rectangular dielectric resonator antennas (DRAs) using HEM_11δ, TE_11δ, and TE_01δ mode were examined to see the radiation pattern, impedance, field distribution and resonant frequency that were achieved when the DRAs were bisected through an image plane by a conducting sheet. The resultant half DRAs are smaller in volume and have a more directional radiation pattern. The elevation angle of maximum radiation was lowered in some cases. Finite-difference time-domain simulation techniques were used     

Optimizing multimode horn feed arrays for offset reflector antennasusing a constrained minimization algorithm to reduce cross polarization

This letter presents an algorithm for suppressing the cross polarization of single offset reflector antennas illuminated by a cluster of multimode horn feeds using a constrained minimization routine. The design variables are the mode ratios for the higher order modes excited in the feeds relative to the dominant TE₁₁ mode. The goal is to systematically determine the optimum mode ratios such that the overall crosspole performance of the reflector antenna improves relative to the single TE₁₁ mode excitation. The multimode horns considered are Potter-type (dual mode) horns and trimode horns     

Design of waveguide narrow-wall short-slot couplers

It is shown that the broad-band coupling properties of narrow-wall short-slot directional couplers and hybrids are due to the effect of the evanescent TE₃₀ mode in the coupling region. This causes a change to the effective phase length of the even-mode circuit, especially when a central tuning element is used. Using the results of a previous paper on the formation of an equivalent circuit from the generalized scattering matrix, an equivalent circuit for the even mode of the coupler is formed, clearly depicting the effect of the TE₃₀ mode     

A note on the cutoff frequency of TE01 mode in TEM cells

It is shown that due to the similarity of the structures of the TEM cell and the finned waveguide, the closed-form expression for the cutoff frequency of the TE₁₀ mode in the finned waveguides can be used to calculate the cutoff frequency of the TE₀₁ mode in the symmetric TEM cells. The results obtained by the expression given agree with various numerical methods to within 1%. The results calculated by this expression are compared with those obtained by an approximate analytical expression