A Proposal of Low-Loss Leaky Waveguide for Submillimeter Waves Transmission

A low-loss dielectric leaky waveguide which carries most of the power in air is proposed for long-distance transmission of submillimeter waves, and its guiding mechanism is fully analyzed by using a two-dimensional slab-waveguide model. It is shown that transmission losses of the guide can become several decibels per kilometer and are not significantly affected by dielectric losses of material used for practical guide parameters.     

Concept of multiorder multimode resonant optical filters

The idea of implementing optical filters by coupling evanescent waves from several diffracted orders into multiple leaky waveguide modes is studied theoretically. Using a dielectric thin-film structure consisting of a coupling grating placed between adjacent waveguides, guided-mode resonance filters exhibiting multiple reflection peaks within a specified wavelength range can be obtained. These peaks originate in the resonant waveguide modes that are excited by the diffracted waves dispersed by the grating. It is shown that this device can be used to realize multiwavelength as well as wide-band spectral filters.     

Resonant Modes of a Dielectric Rod Resonator Short-Circuited at Both Ends by Parallel Conducting Plates

This paper describes a generalized study for the resonant modes of a dielectric rod resonater placed between two parallel conducting plates. Dielectric and conductor losses are ignored. It is shown that there are two resonant states in this resonator, trapped and leaky states. In order to determine the cutoff and resonat frequencies in the trapped state, numerical results are given for the cutoff conditions and dispersive characteristics of a dielectric rod waveguide. The field patterns for the hybrid modes are also presented. For the resonant modes in the leaky state, it is shown to be useful to introduce a complex angular frequency. Numerical results are given for the various modes with different values of the dielectric constant. Generalized mode charts covering both states and including the cutoff conditions are presented. The existence of both states has been verified by experiments.     

Frequency-selective transmission by a leaky parallel-plate-like waveguide

The phenomena of high frequency-selective transmission of a plane wave by a dielectric two-dimensional (2-D) periodic waveguide, comprising a uniform dielectric layer sandwiched by two finite thickness 2-D periodic structures served as the waveguide wall is described. This structure is termed a leaky parallel-plate-like waveguide because the waveguide walls are not perfect reflection mirrors. The scattering characteristics and dispersion relation, including the phase and attenuation constants, of the 2-D periodic waveguide are thoroughly analyzed with the modal transmission-line method and Floquet theory. The extraordinary open stopbands caused by the contra-flow coupling between a leaky parallel-plate-like waveguide and the leaky waves, which are generated by 2-D periodic structures (waveguide walls), are displayed in the form of the Brillouin diagram. The phase-match condition is used to verify the resonant coupling between the incident plane wave and the leaky parallel-plate-like waveguide modes. Specifically, the transmission peak frequencies are accurately predicted.     

复杂环境对漏泄圆波导辐射特性的影响

漏泄圆波导应用于城市轨道交通时, 其辐射特性容易受到其附近复杂环境的影响, 进而影响到无线通信系统的正常运行.以雪覆盖为例, 研究了不同厚度、不同湿度的雪对漏泄圆波导辐射特性的影响, 提出了抵抗恶劣环境影响的措施.结果表明:积雪对漏泄圆波导的近场场强影响比较明显, 且波导的远场随雪湿度与厚度的增大而降低; 通过在漏泄波导表面加一层介电常数接近空气的泡沫塑料层, 可以有效降低雪对漏泄波导辐射特性的影响, 从而提高无线通信系统的可靠性.       

Cerenkov radiation in slow-wave guiding structures

Cerenkov radiation of a prebunched beam in a dielectric tube waveguide is here shown to be about an order of magnitude higher than that in a comparable slab of dielectric material. Furthermore, two distinct types of interaction are analyzed: multibunch, and bunch-by-bunch radiation, wherein integral transform methods are used. Multibunch Cerenkov radiation in a helix waveguide is used to show the identity with TWT interaction. It is subsequently shown that for open boundary inhomogeneous waveguides a TWT type analysis will give the same results as multibunch Cerenkov radiation based on integral transform methods. For single bunch or a bunch-by-bunch type of interaction in such structures where energy orthogonality and completeness of the eigenfunctions do not hold, an integral transform method is used. The underlying difference between bunch-by-bunch and multibunch radiation is discussed. The utility of Cerenkov radiation in a dielectric tube waveguide for the generation of coherent electromagnetic power in the millimeter range is pointed out. Numerical results are given to show the variation of power with respect to various parameters. Experimental results from a 0.8-Mev beam are shown to agree satisfactorily with theory.     

Leaky NRD guide fed microwave planar antenna

A novel and unique application of leaky waveguides as feeding systems for microwave planar antennas is presented. A new leaky nonradiative dielectric (NRD) guide based on a grating structure is proposed, and a planar array slot antenna using this leaky waveguide is constructed and measured at 23 GHz.<>     

Fiber-coupled short Fabry-Perot resonators

An air-gap Fabry-Perot resonator with plane mirrors between closely spaced fiber ends may yield low throughput because of the poor match between the modes of typical single-mode fibers and the resonant mode in the air-gap cavity. The throughput can be improved by confining the resonant mode by a hollow dielectric tube placed inside the resonator. Short fiber-coupled Fabry-Perot resonators with and without an inserted hollow dielectric waveguide and expressions for their transmission losses are derived. It is shown that the throughput of both types of resonator can be improved significantly by using fiber with large mode size to couple to the resonator. The special fiber is then spliced to a conventional single-mode fiber. It is concluded that the resonator with an inserted hollow dielectric waveguide offers increased throughput for resonators with high finesse     

Leaky NRD guide as a feeder for microwave planar antennas

Although leaky wave antennas have been studied extensively in the literature, their practical use is still limited. This work proposes a novel and unique application of leaky NRD guides as feeding systems for microwave planar antennas and shows their substantial possibilities of practical use. At first a new leaky waveguide is introduced based on a periodic array of grooves on the upper side of the dielectric strip in the NRD guide. Then, leaky waves issuing from this configuration are used to feed a slot array cut on the upper metal plate of the NRD guide. Design examples of linearly and circularly polarized planar antennas were constructed, and their characteristics were measured at 23 GHz. The obtained results show the validity for this application of the leaky waveguide     

Anomalous Low-Loss Transmission in a Gas-Confined Dielectric Waveguide for Millimeter and Submillimeter Wavelengths

A novel low-loss (gas-confined) dielectric waveguide for millimeter and submillimeter wavelengths was previously reported by the author. The waveguide consists of a thin dielectric tube separating an internal high-dielectric-constant gas from an external low-dielectric-constant gas. The attenuation constant of this form of waveguide usually increases with increasing tube thickness. The thick tube is indispensable for a mechanically stable waveguide. In this paper, anomalous low-loss transmission characteristics in a gas-confined dielectric waveguide with a thick tube are described. Some condtions are theoretically found where the attenuation constant of the waveguide with a thick tube is extremely low, due to tight field confinement within the internal gas. A qualitative explanation of the operation mechanism is also given.     

Helix Leaky Waveguide

The propagation characteristics of leaky waves in a helix waveguide covered with a slitted cylinder are presented by a method of transverse network representation. The main interest is in helix waveguides with small pitch angles, characterized by a hybrid mode consisting of TE/sub 01/, and a small amount of TM/sub 01/ modes. The leaky wave discussed in this paper may then be regarded as a perturbation of the TM/sub 01/ wave by the slitted cylinder outside the helix. The radiation, metal, and dielectric losses are calculated numerically at a frequency of 50 GHz. The relation between the radiation loss and aperture angle of slit is very different from that of an ordinary leaky waveguide composed of a slitted cylinder without helix, especially when the distance between the helix and shield cylinder is about a quarter of the radial wavelength. The metal and dielectric losses are the same order as radiation loss, however the dielectric loss decreases as the power factor /spl epsiv/"/ /spl epsiv/' increases. The measured total attenuation constant averages about 5 dB/km, almost twice the theoretical value.     

Leaky modes and rays on multimode step-index waveguides?a comparison

It is shown that, by incorporating a lateral shift for leaky rays into a more accurate expression for leaky-ray power attenuation, excellent agreement is obtained with exact numerical values of strongly leaky mode power attenuation on both slab and round waveguides with waveguide parameters as low as 10.     

An integral equation analysis of an infinite array of rectangulardielectric waveguides

An integral equation analysis is applied to the study of the propagation characteristics of an infinite array of dielectric waveguides. The geometry under study is assumed to be rectangular. To find the Green's function of the structure, the Floquet theorem is applied such that the mutual coupling between dielectric waveguide elements is effectively included in the analysis. The effect of the coupling on the propagation characteristics of a dielectric waveguide is studied by varying the size of the Floquet cell. The validity of this analysis to simulate the case of an open dielectric waveguide is confirmed by a comparison with previous results, this in spite of the fact that radiation and leaky wave modes are not accounted for. The complex modes due to the periodicity of the structure are found and their properties are described. The analysis presented, with minor modification, can deal with the problems of dielectric image lines, or dielectric-loaded metallic waveguides     

Rigorous boundary integral equation solution for general isotropicand uniaxial anisotropic dielectric waveguides in multilayered mediaincluding losses, gain and leakage

Bounded and leaky eigenmodes of arbitrary shaped polygonal dielectric waveguides embedded in a multilayered medium are determined based on a rigorous full-wave analysis. The dielectric waveguides consist of isotropic or uniaxial anisotropic material. Losses and gain inside the layers and the waveguides are allowed. The eigenmodes are determined with a boundary integral equation technique in conjunction with the method of moments. Results for the propagation constants are presented for a number of waveguides and, where possible, compared with published data. Special attention is devoted to the transition from a dielectric waveguide to a perfectly conducting waveguide when the loss tangent of the waveguide material changes from zero to infinity     

A single-layer slotted leaky waveguide array antenna for mobilereception of direct broadcast from satellite

This paper proposes a single-layer slotted leaky waveguide array antenna for mobile DBS reception. A single-layer feed structure is proposed, where the feed waveguide is in the same layer as the radiating waveguides. This results in the simple fabrication of slotted waveguide arrays, suitable for mass production. Short radiating leaky waveguides are used to get a large beam-tilting angle of about 50° for the horizontal installation of the antenna and a beamwidth broad enough to dispense with mechanical steering in the elevation plane. A prototype antenna sized 30 cm by 21 cm has a maximum of 74% efficiency and more than 69% efficiency within the DBS band. It also has a broad l-dB beamwidth of 7.5° in the elevation plane, which enables clear DBS reception by a picture tube display over about one-third the area of Japan without elevation tracking     

Resonant type leaky-wave antenna using image NRD guide

A novel leaky-wave antenna constructed from an image non-radiating dielectric waveguide (INRDG) is presented. Unlike conventional leaky-wave antennas, the broadside radiation is realised by utilising the resonant characteristic of the leaky INRDG waveguide mode. Experimental results measured at Ku band confirm the effective performance of the antenna.     

Selective Excitation of Improper Waves of a Round Open Dielectric Waveguide

Journal of Communications Technology and Electronics - Experimental results on selective excitation of improper waves and leaky wave of a round open dielectric waveguide are obtained using an...     

基于漏波电磁透镜的高速飞行列车无线接入研究

随着高速铁路近几年的迅猛发展,下一代交通技术也正渐渐突破桎梏.当前制约轮轨高铁发展的关键因素是稠密大气,真空管道高速飞行列车是一种新型轨道交通技术,它突破了介质限制,利用磁浮技术,可实现列车在接近真空的密闭管道中超高速（大于1 000 km/h）行驶.为解决列车运行在全封闭金属管道中,路边基站信号无法穿透管道壁与列车建立无线链路的问题,文中采用漏泄波导方式来实现管道内无线覆盖.通过特殊的漏泄波导缝隙设计,使得漏泄电磁波在管道腔体内以柱面波形式向列车辐射,从而有效抑制超高速带来的极高Doppler频移.在列车侧,提出一种车顶电磁介质透镜结构,漏泄波导辐射信号可透过透镜直达车内用户,从而实现车载结构与漏泄波导间有效的、无缝的上、下行通信.基于人工介质厚度与相位的定量关系来设计电磁透镜,使得电磁波透过透镜后从柱面波转化为平面波,从而实现更均匀的车厢内无线覆盖.     

3D Printed Terahertz Focusing Grating Couplers

We have designed, constructed and characterized a grating that focuses electromagnetic radiation at specific frequencies out of a dielectric waveguide. A simple theoretical model predicts the focusing behaviour of these chirped gratings, along with numerical results that support our assumptions and improved the grating geometry. The leaky waveguide was 3D printed and characterized at 120 GHz demonstrating its potential for manipulating terahertz waves.     

Analysis and design of a novel leaky YIG film guided wave opticalisolator

A guided wave optical isolator using a four layered leaky yttrium iron garnet (YIG) waveguide with a YIG guiding layer is proposed and analyzed through a transfer matrix formulation. The dependence of isolation characteristics on different waveguide parameters are discussed. It is shown that for four layered structures an isolation ratio of about 24 dB can be achieved with YIG films having large gyrotropy. It is also shown that by replacing the single guiding YIG film with multilayers of YIG with compensated walls and proper permittivity, high isolation ratio can be achieved even with currently available YIG films having low gyrotropy