Determination of simple equivalent circuits of interactingdiscontinuities in waveguides or transmission lines

It is well known that the generalized scattering matrix (GSM) of a microwave network, which includes one or more ports supporting evanescent modes, is nonunitary. This has hindered the formation of equivalent circuits since it has not been evident how to form the impedance or admittance matrix. This paper describes how the problem has been overcome, resulting in a method for the formation of simple equivalent circuits of interacting closely spaced discontinuities in a waveguide. The n-port immittance matrix corresponding to the nonunitary GSM is formed by normalizing the imittance matrix to real or imaginary portal impedances. As an example, an equivalent circuit for the even mode of a waveguide short-slot coupler is presented, and the effect of the evanescent TE₃₀ mode in the coupling region is clearly expressed by an evanescent-mode waveguide in parallel with one supporting the dominant propagating mode. The method should find wide applications to problems involving interactions in waveguides     

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%     

A Novel Band-Reject Element for Pseudoelliptic Bandstop Filters

A novel band-reject element for the design of inline waveguide pseudoelliptic band-reject filters is introduced. The element consists of an offset partial-height post in a rectangular waveguide in which the dominant TE₁₀ mode is propagating. The location of the attenuation pole is primarily determined by the height of the post that generates it. The element allows the implementation of weak, as well as strong coupling coefficients that are encountered in asymmetric band-reject responses with broad stopbands. The coupling strength is controlled by the offset of the post with respect to the center of the main waveguide. The posts are separated by uniform sections of the main waveguide. An equivalent low-pass circuit based on the extracted pole technique is first used in a preliminary design. An improved equivalent low-pass circuit that includes a more accurate equivalent circuit of the band-reject element is then introduced. A synthesis method of the enhanced network is also presented. Filters based on the introduced element are designed, fabricated, and tested. Good agreement between measured and simulated results is achieved     

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。     

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     

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     

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     

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.     

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 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     

A low-loss bandpass filter using electrically coupled high-Q TM01δ dielectric rod resonators

For a TM_01δ mode dielectric rod resonator placed coaxially in a TM₀₁ cutoff circular waveguide, characteristics such as the resonant frequency, its temperature coefficient, the unloaded Q, and the other resonances are discussed on the bases of accurate calculations using the mode-matching method. The results show that this resonator compares favorably with a conventional TE_01δ mode dielectric resonator, particularly for realization of a high unloaded Q. Analytical results also verify that interresonator coupling between these two resonators can be expressed equivalently by a capacitively coupled LC resonant circuit. A four-stage Chebyshev filter having a ripple of 0.035 dB and an equiripple bandwidth of 27 MHz at a center frequency of 11.958 GHz was fabricated using these resonators. Its insertion loss is 0.5 dB, which corresponds to an unloaded Q of 17000, and no spurious response appears in the frequency range below 17 GHz     

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...     

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     

Dielectric ring-gap resonator for application in MMIC's

A dielectric resonator, the dielectric ring-gap resonator, is introduced and analyzed. The dielectric ring-gap resonator is obtained by sawing a narrow gap into a dielectric resonator. Resonant frequencies and unloaded Q-factors of quasi-TE_0pq mode in the ring-gap resonator have been calculated by an appropriate equivalent circuit starting from the resonant frequencies and the field distributions of the TE_0pq modes in the ring resonator. The calculated resonant frequencies of the fundamental quasi-TE₀₁₁ mode show an accuracy of <1% compared with the experimental results. Coupling techniques to couple the ring-gap resonator to a microstrip line on a thin substrate, using the electric fringing field near the gap, have been experimentally investigated. A rigorous method for determining resonant frequencies and field distributions of TE modes in a multicomposite multilayered cylindrical resonator is presented. This resonator consists of numbers of cylinders that are arbitrarily layered in the axial direction     

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     

On internal higher order mode coupling in slot arrays

Internal higher-order mode coupling between adjacent longitudinal radiating slots cut in a broad wall of a rectangular waveguide is examined rigorously. Method-of-moments solutions to pertinent coupled integral equations are investigated. Higher-order mode coupling effects on the amplitude and phase of the aperture electric field are studied as a function of waveguide and slot parameters. It is shown that higher-order mode coupling effects are accounted for, to a substantial extent in standard-height waveguides and almost completely in reduced-height waveguides, by including the TE₂₀ mode coupling in the analysis     

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     

Behavior of the first higher-order modes of a circular core opticalfiber whose core cross-section changes into an ellipse

The vector finite element method is used for investigating the behavior of a set of the first higher-order, four-fold degenerate modes (TE₀₁, TM₀₁, and two-fold degenerate HE₂₁ modes) of a circular core optical fiber whose core cross-section changes into an ellipse. It is found that the TE₀₁ mode becomes the first higher-order mode polarized along the minor axis, E ₂₁^y mode, in a dual-mode region. The remaining three modes become, respectively, the first higher-order mode polarized along the major axis, E₂₁^x mode, and the second higher-order modes polarized along the major and minor axes, E₁₂ ^x and E₁₂^y modes, in the order of magnitude of the effective index. It is also found that the effective index of the E₂₁^x mode is smaller than that of the E₂₁^y mode in a small ellipticity region     

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     

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.