Spontaneous emission and gain in a waveguide free-electron laser

A free-electron laser (FEL) enclosed in a waveguide of narrowly spaced parallel plates has been proposed as a compact, coherent source of far-infrared radiation. The spontaneous emission and small-signal gain of such a device are analyzed. Maxwell's equations are solved for the fields of a relativistic electron beam passing through a linearly polarized undulator in the presence of a parallel-plane waveguide. The radiation intensity is resolved into its component waveguide modes for the fundamental frequency and for all harmonics. The intensity profile in a given harmonic mode is altered significantly when a parameter involving the undulator period, beam energy, and transverse dimension of the guide is such that the radiation group velocity is close to the electrons' axial velocity. The small-signal gain in the waveguide FEL is calculated and related to the spontaneous emission. Near zero slip, the gain curve is significantly different from that of a free-space FEL with the same parameters     

A unique method for reducing losses of bends in dielectric optical wave guide

The dielectric optical wave guide is finding growing attention at millimeter wave frequencies. However the dielectric optical waveguide radiates at bends and thus transmission loss increases. These radiations are in the outword direction of bends. This output radiation at output bends arises due to change in phase velocities of the propagating wave at the centre of the dielectric guide and the phase velocity at the outer surface of the dielectric guide. A unique methiod is suggested to avoid these radiation losses.Experimental results are also shown at microwave frequencies.     

The Groove Guide, a Low-Loss Waveguide for Millimeter Waves

A new waveguide for the low-loss transmission of millimeter waves is presented. The guide consists of two parallel conducting walls with grooves in the central region of the guide cross section. The grooves run along the guide in the direction of the wave propagation. It is shown that the waveguide, if excited in the TE-wave mode, has properties similar to those of the H guide, which contains a dielectric slab between the conducting walls in the center. The new guide is characterized by an exponential transverse decrease of the field distributions in direction from the center and by low attenuation. Theoretical considerations dealing with the field distribution and the data of the guide are presented.     

Scattering of Surface Waves by Discontinuities on a Unidirectionally Conducting Screen

It is shown that a plane screen consisting of closely-spaced parallel wires which are separated from one another and which are such that the radius of the wires and the spacing between them are small in comparison to wavelength, can support a surface wave, the spread of whose field components depends only on the angle which the direction of propagation makes with the direction of the wires. The problem of radiation from a discontinuity in such a semi-infinite waveguide is studied for the following three types of discontinuities: 1) when the waveguide terminates in empty space, 2) when it terminates at another such semi-infinite waveguide having different propagation characteristics, and 3) when it terminates at a perfectly conducting half-plane. In each case, the power reflection coefficient, where applicable the power transmission coefficient, the loss of power due to radiation, and its angular distribution are evaluated. The motivation for this investigation is briefly indicated.     

Diffraction from an abruptly terminated dielectric slab waveguide in the presence of a cylindrical scatterer

The efficiency of using an adaptor lens in front of an abruptly terminated symmetric slab optical waveguide is examined analytically in this paper. The adaptor lens is assumed to be of cylindrical shape with a constant refractive index. The coupling of the modes propagating inside the slab guide into radiation waves in the presence of the lens is treated by integral equation methods. In the first step an integral equation is derived for the Green's functionG(r/r')of an abruptly terminated slab waveguide. The integral equation is solved approximately by an iterative procedure giving accurate results when the difference of the refractive indices between the slab waveguide and substrate-cover regions is small. The Green's function is then used to formulate another integral equation for the unknown field inside the adaptor lens. The latter integral equation for the cylindrical lens cross section area is solved by adopting a cylindrical partial wave expansion for the unknown interior field. After determining this field, the reflection-coupling coefficients for the guided modes propagating in the opposite direction of the incident wave, are computed by using the Green's functionG(r/r'). Radiation patterns are also derived in the far field region for an incident slab guided mode. Numerical results are computed and presented for several guide dimensions, lens radii, and refractive indices.     

Plasma travelling wave antenna

The possibility of using plasma column as linear travelling wave antenna is studied. It is shown that surface current waves propagating in plasma column of finite length are a source of paraxial electromagnetic radiation of decimeter band. Influence of dielectric waveguide, which surrounds cold isotropic plasma, on dispersion properties of plasma column is investigated. The corresponding dispersion equation for eigenwaves of circular dielectric waveguide filled with plasma is derived and solved numerically. Plasma and waveguide parameters are determined under which the surface wave slowing-down is close to unity leading to antenna’s radiation primarily in axial direction. It is shown that in case of plasma density around 10¹²−10¹³ cm⁻³ dispersion of the considered wave is close to dispersion of waves propagating in metal travelling wave antenna.     

A Novel Low-Loss Dielectric Waveguide for Millimeter and Submillimeter Wavelengths

This paper describes a novel dielectric (gas confined) wave guide which consists of a thin dielectric tube separating an internal high-dielectric-constant gas from an external low-dielectric-constant gas. The attenuation constant, fractional power flow, and radiation Ioss of this waveguide are calculated and compared with those of a conventional O-guide (a dieletric tube waveguide). The advantage of the gas-confined guide is that the attenuation constant is decreased involving no bending loss increase due to tight field confinement within the low-loss internal gas. Experimental investigations are carried out to verify the low-loss property of the gas-confined guide. An attenuation constant less than 0.4 dB/m is obtained over the 80-200-GHz range.     

TE Modes of the Dielectric Loaded Trough Line

The properties of TE modes on a dielectric loaded trough waveguide have been investigated. In the case of the dominant mode of this line (TE/sub 20/), families of design curves giving the field distribution, guide wavelength, power handling capability, wall losses, and dielectric losses as a function of operating wavelength, waveguide dimensions and dielectric constant are presented. For a loosely bound wave, the losses are comparable to those of conventional rectangular waveguide and the power handling capability is an order of magnitude greater. The apparatus and procedure used to measure guide wavelength, rate of field decay in the transverse direction, and attenuation are described. The measured performance is in close agreement with the theoretically predicted characteristics.     

含单负材料对称三层平板波导的模式特性

由电磁场的波动方程和边界条件建立了单负材料作为芯层的对称三层平板波导的模式本征方程,用图解法研究其色散特性。研究发现,单负介质波导不支持快波的传播,只支持表面波的传播。在负磁材料平板波导中只存在TE表面模,不存在TM表面模。分析了在负磁材料平板波导中TE模受磁导率的比值-μ2／μ1和波导参数的影响,给出了横向场分布图。在-μ2/μ1〈1时,偶对称只有TE0表面模存在,奇对称只有TE1表面模存在,高阶模式并不存在,且两种模式都没有低频截止;-μ2/μ1〉1时,TE1表面模始终不出现;TE0模的存在与否和波导参数有关,在一定条件下TE0模可出现双模并存。给出的结果可望对表面波器件的设计提供理论基础。     

A hybrid dielectric slab-beam waveguide for the sub-millimeter waveregion

A hybrid dielectric-slab-beam waveguide is suggested which should be well suited as a transmission medium for the design of planar quasi-optical integrated circuits and devices operating in the millimeter- and sub-millimeter-wave regions. The guide consists of a grounded dielectric slab in which a sequence of equally spaced cylindrical lenses is fabricated. The center line of the slab guide is the axis of the lenses. The structure uses two distinct waveguiding principles in conjunction to guide electromagnetic waves. In the direction normal to the slab surface, the guided fields behave as surface waves of the slab guide; their energy is largely confined to the interior of the dielectric and they are guided by total reflection at the slab surface. In the lateral direction the waves behave as Gauss-Hermite-beam modes that are guided by the lenses, which periodically reconstitute their cross sectional phase distribution, resulting in a wave beam that is iterated with the lens spacing. The guided fields are in effect TE and TM modes. The analysis of the new guiding structure is analyzed, the mode spectrum is calculated, and the iteration loss due to the finite size of the lenses is estimated     

Reflection analysis for planar surface wave antennas with different tapering profiles

The reflection characteristics of the planar surface wave antennas with different tapering profiles are analyzed by a method which transforms the radiation problem into the transmission problem of the eigen mode in the partially dielectric filled planar waveguide to avoid the difficulty of the field source problem which is met in the traditional analysis. As a result, the analysis procedure is tremendously simplified. The effect of the tapering profile on the reflection property is carefully investigated and extensive numerical results are given to establish useful guidelines for the design of the planar surface wave antennas.     

基片表面的倾斜度对光学势阱的影响

为了研究原子光刻实验中基片对汇聚激光场的影响,基于几何光学,采用数值仿真的方法,研究了基片表面的倾斜度对光学势阱的影响。结果表明,当基片表面相对于激光驻波中轴线正倾斜时,基片表面会形成一个无光场区,使光学势阱为0,且在z方向上光学势阱会发生一个零值突变;当基片表面相对于驻波中轴线负倾斜时,基片表面永远存在光场,在z方向上光学势阱不会发生零值突变,且光学势阱相对于z=0会出现对称现象。该研究结果对激光汇聚原子沉积实验具有指导意义。     

Scattering of Guided Modes Caused by an Arbitrarily Shaped Broken End in a Dielectric Slab Waveguide

Electromagnetic scattering of guided modes in a dielectric slab waveguide caused by an arbitrarily shaped broken end is analyzed theoretically by using the integral equation method. By solving the integral equations iteratively, the tangential components of the electric and magnetic fields on the broken end surface are determined, from which the reflected mode power, the radiation wave power and field patterns, and the total scattered power are obtained. Numerical results are presented for the plane-perpendicular, plane-tilted, and arc-shaped end surfaces. Both TE and TM modes are assumed as an incident wave.     

A Ferrite Boundary-Value Problem in a Rectangular Waveguide

A solution is obtained for the electric field at the air-ferrite interface (z=0) in a rectangular waveguide filled with ferrite in the semi-infinite half (z>0) and magnetized in the direction of the electric field. The field is expressed in terms of a Neumann series obtained by iteration of a singular integral equation which satisfies the boundary conditions at the interface. The equivalent circuit for the junction is also presented.     

Radiation from a Rectangular Waveguide Filled with Ferrite

This paper presents an approximate analytical solution to the problem of radiation from a ferrite-filled rectangular waveguide. The field distribution at the mouth of the guide is assumed to be unaffected by the termination of the guide. The vector Huygens' principle is applied to find the far-zone radiation field from the determined aperture field. The solution to the problem is found in this manner for the cases of longitudinal and transverse magnetization of the ferrite. The transverse magnetization case is supplemented with a discussion of a specfic numerical example which includes plots of the aperture field distribution and the phase angle as well as plots of the far-zone radiation field. The experimentally known phenomenon of the effect of the applied magnetic field upon the shift of the main lobe is demonstrated and verified analytically.     

Radiation and absorption losses of the whispering-gallery-modedielectric resonators excited by a dielectric waveguide

The scattering of a surface wave of a dielectric layer backed by a ground plane from the whispering-gallery-mode dielectric resonators is considered by use of the surface potential approach and analytical regularization. Efficient numerical algorithms have been developed with applications to the bandstop filter design. Transmitted and reflected power fractions and radiation and absorption losses are calculated and compared for two alternative field polarizations. The effect of excitation of the higher order modes of the waveguide is also studied     

基于光子带隙的双平板太赫兹传输系统研究

研究了一种利用光子晶体带隙特性工作的双平板太赫兹传输系统,它结合了光子晶体波导传输能量集中、损耗低以及双平板波导低色散和单模传输的优点.具体设计了工作在O.32THz的传输系统,研究结果表明:光子晶体双平板波导不但可以实现单模的高效传输,而且也具有良好的输入输出匹配性能.该设计中,采用矩形波导的输入输出结构在316～360 GHz的带宽内可以获得S11<-10 dB的匹配.而且,和普通双平板波导相比更具有结构紧凑、易于集成等优点,因此具有较高的实用价值.     

Metal Walls in Close Proximity to a Dielectric Waveguide Antenna

The effect of placing metal walls in close proximity to a dielectric antenna has been examined theoretically. When these walls are less than one millimeter away from a silicon dielectric waveguide operating nominally at 60 GHz, they affect the wavelength of the electromagnetic radiation within the guide. As the guide wavelength changes, the angle of radiated energy emanating from the metal stripe perturbations on the upper surface of the dielectric guide also changes. A line scanning antenna can be realized by varying the change in guide wavelength in a controlled manner. Theoretical calculations were made to determine the physical parameters such as waveguide size, spacing of metal stripe perturbations and location of metal walls with respect to the silicon waveguide which can produce a large angular scan. Design curves are presented which can be used to examine tradeoffs between the initial radiation angle and range of angular scan as a function of frequency and perturbation spacing. A means of electronically controlling the simulated absence or presence of metal walls by current biasing distributed p-i-n diodes attached to the side of the dielectric guide from a nonconducting state into a high conductivity state is discussed.     

A new equivalent network method for analyzing discontinuityproperties of open dielectric waveguides

A novel network approach is proposed for analyzing interacting discontinuities on open planar dielectric waveguides by accurately taking account of both surface modes and waves with continuous spectra. In this approach, a continuum of the radiation wave is recomposed into a set of the newly defined spectral composite modes, each of which carries a finite magnitude of radiation power. These new modes, in conjunction with surface modes, construct the complete orthonormal set for expressing an arbitrary local field on a dielectric slab waveguide. This leads to an equivalent network approach effective for solving discontinuity problems, even on an open waveguide using the conventional method for closed-waveguide problems. A number of numerical results are shown to demonstrate the usefulness of the proposed approach     

Modal Analysis of a Planar Dielectric Strip Waveguide for Millimeter-Wave Integrated Circuits

A novel planar waveguide which is suitable for guiding electromagnetic (EM) energy in the millimeter-wave and submillimeter- wave regions is studied. By using Wiener-Hopf techniques, we first determine the reflection coefficient at the open ends of the guide. Next, a transverse resonance condition is applied to determine the dispersion relation of the modal field. The propagation constant is found to be complex. Its imaginary part accounts for the edge diffraction loss of the strip through the open ends of the guide. Extensive numerical results are given for the disperson characteristics and modal field distributions for silicon and fuzed quartz substrates. The planar strip waveguide should have the advantages of simplicity in processing, a lower random diffraction loss, and accessibility to monolithic integration techniques.