Transmission Characteristics of Spherical TE and TM Modes in Conical Waveguides (Short Papers)

The transmission properties of spherical TE and TM modes in a perfectly conducting conical waveguide are treated in detail. To start with, an analytically simple and highly accurate digital-computer based iterative algorithm has been employed to evaluate the eigenvalues associated with the spherical TE and TM modes within the guide irrespective of the flare angle (2alpha/sub 0/) of the conical waveguide (theta < 2alpha/sub 0/ < 360/spl deg/). Subsequently, explicit expressions for the attenuation constant, phase constant, phase velocity, and wave impedance are obtained for the spherical modes transmitted within the guide. Accurate eigenvalues obtained numerically are used to study the variation of attenuation constant, phase constant, phase velocity, and wave impedance as a function of the radial distance from the apex with alpha/sub 0/ as a parameter. Measured data on the phase constant of a conical waveguide for the TE/sub 11/ mode have been compared with the analytical results obtained by calculation and an excellent agreement between the two justifies the validity of the analysis presented. Finally, a study of the phase coherence between the dominant spherical TE and TM modes within the guide is presented which may be fruitfully employed in the design of dual-mode conical waveguides.     

The Transmission of TE/sub 01/ Wave in Helix Waveguides

Relations are investigated between the transmission characteristics of a helix waveguide and its surface impedance in regions where any simple approximate formulas are not available because of the magnitude of the surface impedance. The numericaf calculations show that, for any given value of the surface impedance and the angular mode index, there exist an infinite number of different modes which are distinguishable from each other by different values of the radial propagation content. Selecting a mode with minimum attenuation for each given surface impedance, we can draw the equiattenuation lines, connecting these points of equal attenuation on the complex surface impedance plane. At some point on the complex surface impedance plane, a maximum value of the minimum attenuation is found. For the TM/sub 0/ mode supported by a helix waveguide 50 mm in diameter, used at a frequency of 50 kmc, this minimax value of the attenuation constant is about 8 neper per meter, and the corresponding value of the surface impedance is about 57.6-j28.8 ohms. The attenuation constants of all the TM/sub 0/ modes corresponding to this optimum value of the surface impedance cannot be smaller than this minimax value. The same kind of calculations are also performed for the two lowest hybrid modes. Physical structures giving the best value of the surface impedance are also suggested.     

Propagation Losses of Guided Modes in an Optical Graded-Index Slab Waveguide with Metal Cladding

Analytical results for propagation Iosses of guided modes in a graded-index slab waveguide (GISW) with metal cladding are presented. When the permittivity in the guiding layer decreases linearly away from the metal surface, the attenuation constant alpha/sub G/ of well-guided modes, TE and TM, is approximately proportional to only the ratio (Delta epsilon/sub i/ / epsilon/sub 0/) / d/sub i/, where Delta epsilon/sub i/ is the increment in the permittivity at the metal surface in the direction of the polarization of optical waves, d/sub i/i is the diffusion depth in this direction, and epsilon/sub 0/ is the permittivity of free space.     

Radiation from Bends in Dielectric Rod Transmission Lines

The radiation from the fundamental mode propagating around curved dielectric rod transmission lines is investigated experimentally with microwave frequencies. Three methods are used to determine the attenuation by radiation: measuring the insertion loss of bends, measuring the Q-factor of ring resonators, and measuring the Q-factor of sections of curved dielectric rod transmission lines terminated by large reflecting plates. The attenuation is found to depend mainly on the combination R lambda/sub 0//sup 2/ / r/sub 0//sup 3/ where R is the radius of curvature, lambda/sub 0/ the free space wavelength and r/sub 0/ a measure of the transverse field extent of the HE/sub 11/ mode. The experimental results are compared with theoretical predictions of other authors. The measured values of the attenuation constant are found to be smaller than the theoretical values. The distribution of the electromagnetic field near bends is recorded using a semiautomatic field plotter. From the field pictures, it can be concluded that the curved dielectric waveguide radiates tangentially from the outer side. The results presented will also be useful for understanding the mechanism of radiation from bent optical waveguides.     

Electromagnetic-Wave Propagation in the Shielded Ring Line

A theoretical analysis is presented of a periodic structure consisting of equally spaced perfectly conducting rings. The dispersion relation satisfied by the Werent modes of the shielded ring line is determined. This analysis shows that cylindrically symmetric modes identical with those of smooth guides and hybrid modes can travel in this periodical structure. The asymptotic values of the dispersion relation show the different properties of these hybrid modes. The EH/sub n1/ modes can be slow, fast, or can travel at light velocity according to the frequency. The EH/sub nq/ (q > 1) modes are fast modes and exchange their cutoff frequencies for particular values of the geometrical parameters of the structure. These theoretical predictions are verified experimentally by recording the dispersion characteristics of the first modes. For deflecting radio-frequency structures, the fundamental EH/sub 11/ mode is interesting. This deflection constant is measured on a /spl pi/ / 2 wave structure.     

Attenuation Constant of Lunar Line and T-Septate Lunar Line

The attenuation constant /spl alpha/ of the lunar line and that of the T-septate lunar line were derived from the average power loss W/sub L/ and the average power transfer W/sub T/ in each line, that is the ratio, W/sub L//2W/sub T/. The average power loss and the average power transfer for the lunar line and for the T-septate lunar line were derived from their respective field functions. The theoretical attenuation constant of a typical lunar line is less than 0.7 db/ 100 ft for frequencies greater than 2000 Mc. The theoretical attenuation constant of a typical T-septate line is less than 0.9 db/ 100 f t for frequencies greater than 1000 Mc. Experimental measurements of the attenuation constant of a T-septate lunar line agree with the theoretical value. In the 200 to 2000 Mc frequency band, the lunar line and the T-septate lunar line offer a compact and light package without an appreciable sacrifice in peak power handling capacity or attenuation.     

Propagation Constant Below Cutoff Frequency in a Circular Waveguide with Conducting Medium

Exact and approximate propagation characteristics of normal modes in the cutoff region of a circular waveguide surrounded by a medium of finite conductivity are discussed. An exact solution is obtained by numerical analysis, and an approximate one is derived by expanding the characteristic equation considering the finite conductivity of the cylinder wall. The computed values are compared with experimental ones. It is shown that the attenuation of TM/sub 01/ mode at frequencies that are much lower than the cutoff frequency is constant, i.e., independent of frequency and the material constants of the external medium, and this mode is the most suitable one for realizing a precision circular piston attenuator.     

Low-Loss Two-Dimensional GaAs Epitaxial Waveguides at 10.6-/spl mu/m Wavelength

The successful fabrication of low-loss two-dimensional GaAs epitaxial waveguides by chemical etching for use in integrated optics at 10.6 /spl mu/m is reported. Selective excitation of specific E/sub pq//sup y/ modes was observed by placing the prism at specific angles in the horizontal plane. Loss measurements showed no increase in attenuationfor lower order E/sub pq//sup y/ modes (as compared to corresponding one-dimensional waveguide modes) when the guide width is 50 /spl mu/m. As the guide width is reduced, there is a significant increase in attenuation as p increases.     

Dielectric Loaded Elliptical Waveguides

Wave propagation in a metallic elliptic waveguide loaded with a dielectric rod or a dielectric lining is investigated theoretically. The mode spectrum for both slow and fast hybrid modes is obtained by numerical solution of the characteristic equations. Correspondence is established between the modes of the loaded and unloaded elliptical waveguides. Typical field plots for /sub e/HE/sub 01/ and /sub 0/EH/sub 01/ modes are presented. Power flow, power loss, and attenuation are obtained using a perturbation method.     

Simulations of microwave characteristics of high-temperature superconducting microstrip lines by using an empirical two-fluid model

A numerical analysis of the microwave propagation characteristics of a high-temperature superconducting microstrip transmission line is presented. It is based on the transmission line theory and empirical two-fluid model which appropriately incorporates the quasiparticle scattering and residual loss of the superconductor. First, the calculated attenuation constant and phase velocity are compared with those predicted by the conventional two-fluid model for a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// microstrip line with a linear substrate, lanthanum aluminate, LaAlO/sub 3/. Next, we have specifically investigated the effects of nonlinear substrate such as strontium titanate, SrTiO/sub 3/, on the attenuation constant and phase velocity. The tunable feature of such a microwave device owing to the nonlinear dielectric ferroelectric is illustrated and discussed.     

矩形隧道中电磁波传播模式的分析

隧道中环境复杂,对电磁波传播特性的研究比较困难.使用软件模拟方法可以实现对连续变化环境中电磁波传播特性的研究,克服了理论研究和实验方法的局限性.研究结果显示:矩形隧道电磁波的传播,是由多种模式共同作用的结果.近场区高次模起主要作用,信号波动剧烈,远场区低次模起主要作用,信号波动平缓.水平极化电磁波的衰减小于垂直极化电磁波的衰减;靠近隧道壁的信号比位于中央位置的信号有更大的衰减和波动.     

Characteristics of Electromagnetic Guided Waves for Communication in Coal Mine Tunnels

We obtain numerical results of the attenuation and phase constants of the lowest order modes in a rectangular tunnel with an axial wire for various values of physical parameters that are important in intramine communications and remote control. Besides the perturbed free modes of the empty guide, a TEM-like mode, which is highly influenced by the wire impedance and location, is identified. Also the excitation mechanisms of the modes are considered from the standpoint of point-to-point communication within a mine tunnel.     

Circular TE/sub 0n/ Mode Filters for Guided Millimeter-Wave Transmission

A millimeter-wave circular TE/sub 01/ mode waveguide generates undesired circularly symmetric modes (TE/sub 02/, TE/sub 03/ modes, etc.) in bends or at discontinuities along a waveguide line. This paper describes the theory and experiment on the TE/sub 02/ and TE/sub 03/ mode filters developed for guided millimeter-wave transmission. The experimental results of two improved TE/sub 03/ mode filters show that the attenuation of the TE/sub 03/ mode is more than 16 dB for one type over the 40-70-GHz range. The TE/sub 01/-mode insertion loss of another type is about 0.2 dB over the 40-80-GHz range. The present mode filters can be applied to various high-speed guided rnillimeter-wave systems currently under development.     

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.     

Radio wave propagation characteristics in lossy circular waveguidessuch as tunnels, mine shafts, and boreholes

We present the characteristics of radio propagation in a circular lossy waveguide whose walls are composed of earth soil materials with frequency-dependent properties. This type of structure is used to represent a radio link for an underground wireless communication channel such as a tunnel, mine shaft, or borehole. We present calculated results of the attenuation constant for various propagation modes in the soil waveguide structure for various soil constituents and moisture levels. Transverse field plots of the various modes for different soil types are also presented. Finally, it is shown that for small |k₂a| (where k₂ is the wavenumber in the soil and a is the radius of the waveguide) some modes in the waveguide disappear and a discussion of this behavior and how it relates to excitation problems is given     

A Simple Method for Spacing the Adjacent Passbands of a Coupled-Line Filter

A bandpass filter using two coupled transmission lines is considered. Two ports of the coupled-line four port are both short-circuited (or open-circuited); the other two ports are terminated in the characteristic impedances of the lines (e.g., 50 Omega). For a constant coupling along the coupling section l the attenuation poles are fixed at l/lambda = n/2 (n = 0,1,2,...). If, however, the coupling changes along the coupling section in three steps with the coupling factors k/sub 1/, k/sub 2/, k/sub 3/ = k/sub 1/, the stopband between two adjacent passbands can be extended for certain values of k/sub 1/ and k/sub 2/. A simple calculation method for the coupling factors k/sub 1/ and k/sub 2/ is described. A practical design example shows good agreement with theoretical results.     

The Elliptical Surface Wave Transmission Line

Electromagnetic wave propagation on an elliptical cross-sectional surface-wave transmission line is investigated theoretically. Characteristic equations for odd and even hybrid modes are derived and solved numerically. Expressions are obtained for power flow, energy storage and power loss using a perturbation method. Numerical results on propagation characteristics of three lower order modes are presented. The /sub 0/HE/sub 11/ mode is shown to have low attenuation particulary at high eccentricities. The propagation characteristics of lines of high eccentricities are found to be slowly varying functions of dimensions.     

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.     

Square and Rectangular Waveguides with Rounded Corners

Eigenfunctions, eigenvalues, and attenuation constants in waveguides are determined for the square with rounded corners, and for the cigar-shaped rectangle with rounded ends. These cross sections allow, by continuous variation of a parameter, the investigation of the deformation of the modes and attenuation curves of a circular waveguide. Particular attention is given to the H/sub01/ mode and its remarkable attenuation curve.     

A Rotary Joint for Two Microwave Transmission Channels of the Same Frequency Band

This paper describes a rotary joint for two microwave transmission channels of the same frequency band. It consists of two pairs of rectangular waveguide terminals, a circular waveguide which transmits both channels, and coupling elements between the rectangular waveguide terminals and the circular waveguide which convert the rectangular H/sub 10/ mode into the circular H/sub 01/ and E/sub 01/ modes. If pure H/sub 01/ and E/sub 01/ modes can be excited, perfect separation of the channels as well as constant amplitudes and phases can be obtained when the joint rotates. While the conversion into the circular E/sub 01/ mode is performed by a conventional method, a new method had to be developed for the conversion of the rectangular H/sub 10/ into the circular H/sub 01/ mode.