隧道中低频导行电磁波的传播特性

在低频段上，导行电磁波的衰减率很小，随频率的升高而缓慢增加，不论单线波模还是双线波模其近壁效应都很小。用数值分析方法术解了单线波模方程和双线波模方程，得出的主要结论为它们的衰减率与隧道壁电导率和隧道半径有撤弱依赖关系。理论分析含单导体的任意横截面隧道可知低频段上导行电磁波的衰减率与隧道横截面积大小有微弱依赖关系，而与横截面形状无关。     

Mode conversion by tunnel nonuniformities in leaky feeder communication systems

Using an idealized theoretical model, the inadvertent mode conversion between the bifilar and monofilar modes are dealt with in a tunnel that contains a braided coaxial cable. The tunnel is allowed to have various kinds of lateral nonuniformities such as changes of wall conductivity and permittivity. We conclude that such effects are very important in understanding leaky feeder systems.     

Calculated Channel Characteristics of a Braided Coaxial Cable in a Mine Tunnel

The braided coaxial cable is studied as a communication scheme in a mine tunnel. A simplified rectangular waveguide model is adopted for the tunnel, and the shield of the cable is assumed to behave as a single inductive transfer impedance. Specific results on the attenuation of the monofilar and bifilar (or coaxial) modes of propagation, taking into account the possible existence of a thin lossy film on the cable, are presented. In order to estimate the maximum possible range of communication, we consider the coupling factors of these modes to transmitting and receiving dipoles inside the tunnel, and we present results on these factors for various cable parameters and over a wide range of frequencies.     

Propagation Along a Coaxial Cable with a Helical Shield

A leaky coaxial cable is modelled by a dielectric coated conductor shielded by a finite number of unidirectional helical wires. A modal equation is derived and soIved numerically for the propagation constants of both the monofilar and bifilar modes. Numerical results are also presented for the effective surface transfer impedance of the shield. This parameter is found to depend, in general, on the propagation constant.     

Electromagnetic Theory of the Loosely Braided Coaxial Cable: Part II--Numerical Results

The general modal equation obtained in Part I is solved numerically for the propagation constants of both the monofilar and bifilar modes. For the special case of an air-filled cable, only one mode is supported. Numerical results are also presented for the surface transfer impedance of the shield which, in general, depends on the propagation constant. The properties of the counterwound helical shield are found to be qualitatively similar to those of the unidirectional helical shield.     

Propagation Along a Braided Coaxial Cable Located Close to a Tunnel Wall (Short Papers)

A previous development is extended to permit attenuation calculations when a braided cable is located close to a tunnel wall. This is an important case in mine communications utilizing leaky feeders. Numerical results are presented to illustrate the effects of numerous parameters on mode attenuation. A principal finding is that the attenuation rate for the bifilar mode is hardly affected at all by the finite conductivity of the wall. On the other hand, the monofilar mode suffers a very high attenuation when the cable approaches the wall.     

双线背射螺旋作馈源的新式背射天线

本文提出一种用双线背射螺旋作馈源的新式背射天线。这种天线具有结构简单，馈电方便，增益较高，易于产生圆极化波等优点。     

不对称传输线理论分析及实验研究

该文在假设双线传输线两线上电流大小相等、方向相反的条件下,运用双线传输线理论思想,推得不对称(电流)双线均匀传输线的电压、电流关系。由此,文中给出了一种分析双线传输线变压器的实用、有效的方法,且理论结果与实测结果具有较好的一致性。     

Field solution and propagation characteristics of monofilar-bifilarmodes of axially slotted coaxial cable

The electromagnetic problem of an infinite, axially slotted coaxial cable is solved. The monofilar and bifilar eigenmodes are obtained with good accuracy and previous conflicting results are discussed. Further, a field solution satisfying the proper boundary conditions is obtained and shown to be essentially azimuthal     

Radiocommunication in tunnels

Two processes for the improvement of a bifilar line used as a support for propagation in an underground gallery are described. They consist in introducing networks on the line to bring about energy exchanges between the two propagation modes which characterise it.     

Axial mode helical antennas

The radiation characteristics of helical antennas operating in the axial mode are evaluated on the basis of the theoretical current distributions and are verified by experimental work. A comparison between monofilar helix and bifilar helix antennas is made, and a helical antenna with a parasitic helix (HAP) is proposed in order to enhance the power gain. It is found that the gain of the HAP in which the parasitic helix is wound from a point diametrically opposite to that of one and one-half turns of the driven helix is about 1 dB higher than that of the monofilar helix. The ratio of the frequency band in which the HAP radiates a circularly polarized wave within an axial ratio of 3 dB is calculated to be 1:1.8.     

Transmission Modes in a Braided Coaxial Cable and Coupling to a Tunnel Environment

Radio frequency transmission in a semicircular tunnel containing a braided coaxial cable is considered. The general formulation accounts for both the ohmic losses in the tunnel wall and a thin lossy film layer on the outer surface of the dielectric jacket of the cable. Using a quasi-static approximation, it is found that the propagation constants of the low-frequency transmission line modes are obtained through the solution of a cubic equation. However, for the special case when the conductivity thickness product of the Iossy film layer vanishes, this cubic equation reduces to a quadratic. The spatially dispersive form of the braid transfer impedance is also accounted for. It is shown that the quasistatic theory is well justified for frequencies as high as 100 MHz for typical tunnel geometries. Finally, special characteristic impedances are derived for the various modes of the equivalent multiconductor transmission line.     

An investigation of the magnetic transverse waves on an electron beam

An electron beam in the presence of an axial magnetic field supports four transverse waves; two cyclotron waves, and two synchronous waves. A general coupling theory is developed from an electronic equation and a circuit equation to describe how these waves can be coupled to traveling-wave circuits. The polarization and power flow characteristics of the waves are derived. The theory is applied to. the bifilar helix, a circuit which can couple selectively to each of the four modes. A bifilar helix traveling-wave tube was used to investigate experimentally the four beam modes and provide a quantitative check of the coupling theory.     

Theory of the Slotted Coaxial Cable

The electromagnetic problem of the coaxial cable with a continuous slot along the outer conductor is solved taking into account the dielectric constant of tbe cable insulation. Cylindrical harmonics expansions for the inner and outer space are used. The basic difficulty is to express boundary conditions on a part of the period in Fourier series. It appears that the singularity of the fields at the edge of the outer conductor plays a key role in the uniqueness of the result. The propagation constants of the monofilar and coaxial modes are obtained with a good accuracy. It is shown that these modes have different transfer inductances.     

Characteristics of Bifilar Helix Circuit

The characteristics of two kinds of bifilar helix circuit are discussed in this paper. One is alike wound bifilar helix and another is contrawound bifilar helix. Alike wound bifilar helix is often used in O-type backward wave tube (BWO). Owing to wider operating bandwidth, higher interaction impedance and large dimensions, the contrawound helix is suitable for broadband millimeter wave traveling wave tube (MMW TWT).     

A Dual Mode Tuning Circuit for Microwave Transistor Oscillators

A two-port circuit adjusting both even and odd mode fields, with orthogonal mode adjustment, can be used as an embedding circuit for a microwave transistor oscillator. The circuit, analyzed in TEM line, may also be realized in any other form of transmission line geometry, including two coexistent modes in a cavity. The resulting oscillator is stable, has low FM noise, and is readily tunable. Analyses of the tuning circuit and oscillator are presented, along with some experimental results and a discussion of methods using other than TEM transmission lines to produce the even and odd modes.     

Radio frequency transmission via a trolley wire in a tunnel with a rail return

An analysis is given for the transmission of electromagnetic waves along a circular tunnel in the presence of axial conductors. One of these conductors is an idealization of a trolley wire with its bonded feeder line that may be located anywhere in the tunnel. The other is a metal rail that is located within the homogeneous rock medium at a finite distance from the tunnel wall. A mode equation for the propagation modes is obtained that is used to obtain numerical results for the attenuation rate in the frequency range 50 to 800 kHz. It is shown that the attenuation rate is only weakly dependent on the burial depth of the rail conductor, at least in the range up to 50 cm. Also, it is found that the rail conductor for the model adopted carries an appreciable fraction of the total return current when typical rock conductivities are assumed. A thin layer of insulation on the rail appears to have a negligible effect. In fact, there is little change even if the rail is within the tunnel and just above the tunnel floor.     

A monofilar spiral antenna and its array above a groundplane-formation of a circularly polarized tilted fan beam

A monofilar spiral antenna is analyzed in the presence of a conducting plane reflector, using the method of moments. The circumference of the spiral antenna is chosen to be 2.3 wavelengths. A tilted beam of circular polarization is realized by superposing the fields from two active regions. The gain of the tilted beam is approximately 8 dB. The frequency bandwidths for 1-dB gain drop and 3-dB axial ratio criterions are 12% and 23%, respectively. An array consisting of the four monofilar spiral antennas is also analyzed, where the array element spacing is chosen to be 0.8 wavelength at a design frequency f₀. The input impedances of the four spirals are almost the same as the impedance of the single monofilar spiral antenna at f₀. The array radiates a tilted fan beam with a gain increase of approximately 6 dB from the gain of the single spiral antenna at f₀. The frequency bandwidth for a 3-dB axial ratio criterion is almost the same as that of the single spiral antenna     

Analysis of the Dedicated Communication Line in a Mine Tunnel for a Shunt-Loaded Trolley Wire

The theory of transmission in a semicircular tunnel containing two axial conductors is simplified for the case of radio frequencies. It is shown that the effect of ohmic losses in the wall can be represented as series impedances per unit length in the equivalent coupled transmission line circuits. This opens the way for a systematic calculation of the mode conversion phenomena that occur when one of the axial conductors has a discrete shunt load to the ground plane. Explicit formulas are obtained for the modal conversion coefficients. These are used to discuss the effect of a shunt load on the trolley wire on the performance of a radio frequency communication system. It is confirmed that the unloaded dedicated communication line provides for a low loss mode that is hardly affected by the shunt load on the adjacent trolley wire in the tunnel.     

矿井感应通信机车插入损耗及专用线理论研究

给出了在矿井中利用电机车架空线进行感应通信时，架空线负载（即电机车）引起的手稿损耗的定义，计算了插入损耗和无负载时的电磁波传输损耗并对比了这两种损耗，可知插入损耗是非常大的，这说明了使用专用感应线的必要性，架设专用感应线后，矿井隧道中将存在一个插入损耗和传输损耗都比较小的波模，利用该波模进行感应通信是可行的。