Circuit Components in Dielectric Image Lines

Symmetry of dipole mode in a dielectric rod permits use of an image system. By replacing lower half of dielectric and its surrounding field with an image surface, support problem is eliminated. Resulting image provides structural convenience and also has very low loss, provided wave is allowed to occupy a cross section many wavelengths square. In millimeter region this is readily achieved. Possibilities of new types of circuit elements in this image system are explored. Combination of optical and waveguide techniques is a characteristic of resulting components. Properties of several transducers between image line and either rectangular waveguide or coaxial line are described. Attenuators, standing-wave detector, and various directional coupler types for image lines are also discussed.     

Quasi-TEM Analysis of Microwave Transmission Lines by the Finite-Element Method

This paper describes a finite-element approach to the quasi-TEM analysis of several different types of isolated and coupled microwave transmission lines. Both the first- and higher order ordinary elements, as well as singular and infinite elements, are used to solve for the potential and field distributions in the cross section of the line. Next, the cross-sectional field distribution is inserted in a variational expression to compute the capacitance per unit length of the line, and the effective permittivity and characteristic impedance of the line are obtained from the capacitance value. A perturbational approach is developed for estimating the losses due to conductor and dielectric dissipation and computing the attenuation constant. Both the upper and lower bounds for the capacitance and the characteristic impedance are found by solving the original and the corresponding dual problem. Lines treatable by this method may contain an arbitrary number of arbitrarily shaped conductors, including a system of conductors placed either above a single ground plane or between two parallel ground planes, and inhomogeneous dielectric regions that can be approximated Iocally by a number of homogeneous subregions. The results obtained using the finite-element procedure have been compared for various types of microwave transmission lines and have been found to agree well with available theoretical and measured data.     

The Calculation and the Measurement of the Coupling Properties of Dielectric Image Lines of Rectangular Cross Section

In this paper the coupling properties of uniformly coupled dielectric image lines of rectangular cross section are calculated employing an exact method for the determination of the phase constants of the even and the odd mode. The theoretical results are verified experimentally. The results are also applied to the calculation of the coupling characteristics of practical dielectric image line directional couplers.     

Analysis of Arbitrarily Oriented Microstrip Transmission Lines in Arbitrarily Shaped Dielectric Media Over a Finite Ground Plane

A numerical analysis is presented for a multiconductor transmission line in multilayered Iossy, dielectric regions where the ground plane is of finite extent. The transmission fines are infinitely long and vary in cross section from finite to infinitesimally thin. The Green's function for such a two-dimensional transmission line involves an arbitrary constant. If the ground plane is infinite, the method of images could be used where this constant cancels out. However, in the case of a finite ground plane, the constant has to be evaluated. Here a numerical method is presented where the constant could be eliminated rather than evaluated by imposing the condition for the total charge to be zero. The transmission lines, dielectric regions, and the ground plane can have arbitrary cross sections.     

Field configurations and propagation constants of modes in hollow rectangular dielectric waveguides

The field configurations and propagation constants of linearly polarized low-loss modes in hollow dielectric waveguides with rectangular cross section are computed analytically under the assumption that the dimensions of the rectangular cross section are much larger than the free-space wavelength. The attenuation constant is then equal to the sum of the corresponding TE- and TM-mode attenuation constants in parallel-plate waveguides.     

Mode-matching analysis of a shielded rectangular dielectric-rod waveguide

Rectangular cross-sectional dielectric waveguides are widely used at millimeter wavelengths. In addition, shielded dielectric resonators having a square cross section are often used as filter elements; however, there is almost no information available on the effect of the shield. Rectangular or square dielectric waveguide is notoriously difficult to analyze because of the singular behavior of the fields at the corners. Most published analyses are for materials with a low dielectric constant, and do not include the effects of a shield. This paper describes a numerically efficient mode-matching method for the analysis of shielded dielectric-rod waveguide, which is applicable to both low and high dielectric-constant materials. The effect of the shield on the propagation behavior is studied. The shield dimensions may be selected such that the shield has a negligible effect so that results can be compared with free-space data. The results are verified by comparison with several sets of published data, and have been confirmed by measurement for a nominal /spl epsiv//sub r/ of 37.4.     

Simple Microwave Technique for Independent Measurement of Sample Size and Dielectric Constant with Results for a Gunn Oscillator System

Standard perturbation theory analysis has been used to develop a new microwave technique for simultaneously and independently measuring the size and dielectric constant of dielectric samples. Gunn flange oscillators have heen used to show that simple and low cost systems give measurement accuracies better than 5 percent when applied to nylon, Teflon, and quartz samples. The techniques should be particularly useful with samples of irregular cross section.     

Propagation characteristics of superconducting microstrip lines

The modified spectral-domain approach is applied to study the propagation characteristics of high temperature superconducting microstrip lines whose signal strip and ground plane are of arbitrary thickness. In this study, numerical results for effective dielectric constant, attenuation constant, and strip current distribution are presented to discuss the effects due to frequency, temperature, strip thickness, and substrate loss tangent. In particular, the conductor and dielectric attenuation constants of superconducting microstrip line are depicted separately to discuss the mechanism of the line losses. A comparison with published theoretical and experimental results is also included to check the accuracy of the new approach's results     

The Measurement of the Radiation Losses in Dielectric Image Line Bends and the Calculation of a Minimum Acceptable Curvature Radius

Measurements of the insertion loss due to radiation curved dielectric image lines of rectangular cross section are described for the frequency range from 26 to 90 GHz. A minimum acceptable curvature radius as a function of the frequency is calculated employing the field distributions of straight dielectric image lines and is compared with measurements.     

Numerical Analysis of the Rectangular Dielectric Waveguide and its Modifications

Dielectric waveguides suitable for millimeter and submillimeter wave integrated circuits are analyzed by applying the generalized telegraphist's equations. The dielectric waveguides treated in this paper are the rectangular dielectric image line, the cladded rectangular dielectric image line, the insulated image guide, and the strip dielectric guide. Numerical results of the propagation constant, the power distribution, and the field configuration in these dielectric waveguides are presented. Values for the propagation constants obtained by our method are compared with other theoretical results. Although this work is based on a closed waveguide model, it may be applicable to wide classes of dielectric waveguides with arbitrary dielectric profiles and cross sections.     

Propagation of waves in rectangular waveguides containing dielectric layers in the H-plane

Rectangular waveguides, containing dielectric layers in the H-plane, are studied. Results on normalized phase constant, cut-off frequency, and attenuation constant under cut-off, are presented for lower-order longitudinal section modes. Data have been computed from characteristic equations obtained by the matching of the tangential field components at the dielectric interfaces.     

Radio propagation characteristics in underground streets crowdedwith pedestrians

Radio propagation characteristics in an underground street crowded with pedestrians are presented. Measurements were carried out on vertical and horizontal polarization characteristics in a frequency range from 250 MHz to 12.4 GHz. In the analysis, the region with pedestrians is modeled as a lossy, homogeneous dielectric slab. Based on the method of effective dielectric constant, some numerical results are presented for the attenuation constant and for the field distribution in the cross section and are compared with experimental data. It is shown that the method is applicable in determining the propagation characteristics in underground streets crowded with pedestrians     

New Materials for Superconductive Communication Cables

The feasibility of superconductive coaxial cables as a communication medium with an enormous capacity may be increased by applying superconductive materials with low surface resistances and high critical temperatures as well as dielectrics with low loss. This paper discusses the mechanisms affecting metallic conduction and dielectric properties of materials in relation to their application in a low temperature transmission line. It starts with a brief report on the present state of rf-superconductivity, but it particularly deals with the measurements of low temperature dielectric microwave losses of polymeric materials, because the dielectric loss mainly determines the overall-attenuation of the cable. Our investigations resulted in the smallest loss tangent of any solid material measured so far:tan delta (4.2 K, 6.5 GHz) = 6.6 dot 10^{-7}pm 5%for polyethylene. This corresponds to a cable attenuation of roughly 0.5 dB/km at 10 GHz and extends the bandwidth of superconductive communication lines appreciably.     

Attenuation of a shielded rectangular dielectric rod waveguide

The attenuation coefficient of a rectangular dielectric line enclosed by a rectangular shield is obtained by the use of a rigorous mode-matching method to calculate the required mode field intensity. The cross section of the waveguide is overlaid by a grid, and numerical integration is used to determine the power flow, dielectric, and conductor losses and respective attenuation coefficients. To obtain experimental verification, a length of waveguide was made into a resonator, and measured and calculated Q factors were compared. The results for the E/sup y//sub 11/ mode show how the influence of the shield decreases with distance. This is relevant to the design of dielectric waveguide structures and in filter applications where dielectric resonators are used.     

A Technique for Measuring the Effective Dielectric Constant of a Mlcrostrip Line

A method is discussed by which the effective dielectric constant of a transmission line of complex cross section is determined experimentally.     

Field Profile In A Single-mode Curved Dielectric Waveguide Of Rectangular Cross Section

An approximate and simple method for predicting the field profile in a curved dielectric waveguide of rectangular cross section is described. For a single-mode propagation, it is shown that the transverse field can be approximated inside the dielectric guide by the Airy function of the first kind and that the radial attenuation constant is a function of the bending radius outside the guide. Experimental verification of the theoretical results is included.     

Transmission of electromagnetic waves in hollow tubes of metal

Electromagnetic energy may be transmitted through the inside of hollow tubes of metal, provided the frequency is greater than a certain critical value; this value is inversely proportional to the tube radius and to the dielectric coefficient for the tube interior. Calculations and measurements of the more important characteristics of this new kind of transmission system have been made, and the conditions for minimum attenuation obtained Terminal devices for connecting a hollow pipe system to a biconductor system and others, in the form of horns, for directly radiating radio waves, have been developed; these electromagnetic horns may also be fed with ordinary coaxial lines. Certain types of terminals act as sharply resonant hollow tube elements. Several independent communication channels may be established within a single pipe line by utilizing distinct types of waves for each channel in a unique kind of multiplex operation. A section of a hollow tube may be used as a high-pass filter. Although presupposing adequate technique for the generation and utilization of the shortest radio waves, this new system possesses several features, among which are a minimum dielectric loss, substantially perfect shielding, and a simplicity of structure.     

Measurements of Attenuation and Phase Velocity of Various Laminate Materials at L-Band

Measured data are plotted for the characteristic impedance, velocity of propagation, and attenuation of dielectric sheet supported strip transmission lines for four dielectric materials: teflon bonded glass cloth, epoxy bonded glass cloth, polyester bonded glass mat, and XXXP paper base phenolic. At 1000 megacycles the teflon material is excellent and the epoxy and polyester materials satisfactory for low Q applications, such as microwave transmission lines.     

Low-Frequency Behavior of the Propagation Constant Along a Thin Wire in an Arbitrarily Shaped Mine Tunnel

Seidel and Wait have investigated the complex propagation constant (phase and attenuation coefficients) of the fundamental mode of propagation for radio waves along a thin wire or cable, located in an elliptical mine tunnel, and found that the attenuation rate for low frequency is insensitive to the shape of the ellipse if the cable-wall distance and cross-sectional area are kept constant. We consider here tunnels of more general cross section, and obtain a characteristic equation for the propagation constant valid for sufficiently low frequency, by means of a variational formulation of an integral equation. The characteristic equation involves only the electrical parameter of the tunnel walls, the radius of the wire, and the capacitance per unit length that the wire would have if the tunnel walls were perfectly conducting. Agreement with exact calculations for several geometries is found to be excellent below about 100 kHz, and acceptable even up to 1 MHz or more, for typical tunnel parameters. Since the wire capacitance can be shown to depend most importantly on its distance from the wall and on the area of the tunnel, the conclusion of Seidel and Wait can be made more precise and extended to tunnels of arbitrary cross section.     

Rapid Measurement of Dielectric Constant and Loss Tangent

The problem of evaluating dielectric constant and loss tangent by the short-circuited-waveguide technique has been encountered continually in recent years in the study of artificial dielectric media and radome materials. In general, practical measurements have involved materials with low loss and dielectric constants less than 10. The analytical method normally applied to data on such materials requires laborious computation. The available graphical methods have not completely eliminated computation and have provided answers of unsatisfactory accuracy. The present paper describes rapid graphical techniques for evaluating dielectric constant and loss tangent from the quantities normally measured with the slotted line, using samples of arbitrarily chosen length. It begins with equations previously derived for the case of low-loss media. By use of a new parameter, the relationship between dielectric constant and the measured shift in standing-wave minimum is plotted in such a way that all possible values of dielectric constant within any predetermined range are read directly from the graph with no computation whatsoever. A graph can be readily prepared to apply over a full range of frequency to all sizes of rectangular waveguide.