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The general theory of coaxial pairs was dealt with in an article on “The Electromagnetic Theory of Coaxial Transmission Lines and Cylindrical Shields” by S. A. Schelkunoff (B. S. T. J., Oct., 1934). The present paper considers a specific aspect of the general theory, namely, crosstalk. Formulae for the crosstalk are developed in terms of the distributed mutual impedance, the constants of the transmission lines and the terminal impedances. Some limiting cases are given special consideration. The theory is then applied to a few special types of coaxial structures studied experimentally and a close agreement is shown between the results of calculations and of laboratory measurements. If the outer members of coaxial pairs are complicated structures rather than solid cylindrical shells, the crosstalk formulae still apply but the mutual impedances and the transmission constants which are involved in these formulae must be determined experimentally since these quantities cannot always be calculated with sufficient accuracy. The crosstalk between coaxial pairs with solid outer conductors rapidly decreases with increasing frequency while the crosstalk between unshielded balanced pairs increases. In the low frequency range there is less crosstalk between such balanced pairs than between coaxial pairs but at high frequencies the reverse is true. The diminution of crosstalk between coaxial pairs with increasing frequency is caused by an ever increasing shielding action furnished by the outer conductors of the pairs. Finally, crosstalk in long lines using coaxial conductors is discussed and the conclusion is reached that, unlike the case of the balanced structure, the far-end crosstalk imposes a more severe condition than the near-end crosstalk in two-way systems which involve more than two coaxial conductors.

The complex dielectric constant of highly purified nitrobenzene in the region of anomalous dispersion has been determined by measuring the input impedance of a variable length of a coaxial transmission line filled with the liquid. The measurements were carried out at frequencies from 0.65 kmcps to 3.00 kmcps in the temperature range between 15°C and 50°C. Good agreement was observed with an expression suggested by Cole and Cole, and the critical frequencies in this temperature region were found to be between 3 and 6 kmcps.

The theory and design of dielectric beads in a coaxial transmission line are discussed. At first the theory of many dielectric beads in a transmission line are discussed briefly. It is shown that by proper choice of the spacing between the adjacent beads the overall reflection produced by all the beads can be minimized. The case of an optimum bead producing minimum reflection is discussed in detail. Broadband characteristics of such a bead is also studied. Finally, the actual design of a bead is carried out.

A microwave instrument for non-destructive testing of the homogeneity of supercalendar rollers used in paper mills is described. The sensor consists of a flat coaxial transmission line a half wavelength long. A sensitivity of more than 0,1% is achieved in measuring small changes in the dielectric constant. Measurement of absolute values of the dielectric constant is also possible.

A reflectionless termination design is described which, in principle, can be adapted to wave‐guide or coaxial transmission lines. Reflection coefficients of 0.001 were obtained experimentally with X‐band wave‐guide terminations. The termination comprises a section of transmission line into which is fitted a tunable sliding load. The sliding load is tuned to be reflectionless by means of the ``sliding load'' method of measuring reflection coefficients. The termination can be operated over a wide frequency range but must be retuned each time the frequency is changed.The wave‐guide circuit of the load is analyzed and design equations are derived.The reflectionless wave‐guide termination is primarily useful as a reference standard for microwave impedance bridges.

A form of circuit which is of considerable interest for the transmission of high frequency currents is one consisting of a cylindrical conducting tube within which a smaller conductor is coaxially placed. Such tubes have found application in radio stations to connect transmitting and receiving apparatus to antennae. As a part of the development work on such coaxial systems, it has been necessary to formulate the theory of transmission over a coaxial circuit and of the shielding against inductive effects which is afforded by the outer conductor. This paper deals generally with the transmission theory of coaxial circuits and extends the theory beyond the range of present application both as regards structure and frequency.

The paper concerns the results of design and performance of a low power coaxially interdigital magnetron with external coupled cavity. Special attention is given to the problem of wide-range tunability, in the microwave frequency spectrum, using either mechanical or voltage-tuning methods. The basic structure of the magnetron consists of a short, hermetically-sealed section of coaxial transmission line which contains six equally spaced radial vanes extending from the inner wall of the outer coaxial cylinder into six longitudinal slots in the inner coaxial cylinder. The cathode is symmetrically located within the inner coaxial cylinder at the position of the multianode structure. This sealed off multi-anode system is used to excite a TEM mode in an external coaxial circuit. Experimental results on electronically and mechanically tunable operation are reported, with particular emphasis on voltage tuning.

A theoretical expression is derived for the relative error on e′ and e′ when measured with the method of Roberts-von Hippel using coaxial transmission lines. This expression is shown to depend on the experimental accuracy of the measureable quantities but also on the characteristic parameters of the sample e′, e″ and its thickness h. Numerical calculations show how in various cases these errors change with h. It is also demonstrated that for polar samples the choice of the thickness of the sample may become critical. Some experimental results are given to illustrate this effect.

Measurements of the dielectric constant of soil containing different known percentages of moisture were made at a fixed frequency of 430 Mc/s. The method adopted involved the use of a coaxial transmission line terminated with a sample of the soil under test The line consisted of a central rod with a concentric tube about 2½ metres in length. Measurements were made with soil samples containing from 4.1% to 47.7% moisture The dielectric constant was found to vary from 4.0 to 31.4 The values are shown graphically and compared with those obtained by nine other authors. The conductivity could not be measured accurately with the method used, but it was estimated to vary from about 1 5 × 109 e.s u with 4% moisture to 4 × 1010 e.s u with 50% moisture

The complete radiation field of a tubular monopole of arbitrary length and radius, which is base driven by a low-impedance coaxial transmission line, is derived. The integral equation for the current distribution, which includes a term for the feed-point correction is solved by the inversion of a matrix under the assumption that the current is a continuous, piecewise linear function. The far-zone electromagnetic field established by this current is expressed in closed form. It is found that the effect of thickness is to round off the nulls predicted by previous theory for vanishingly small radius and to enhance the high-angle radiation.

Numerical "shooting" methods are employed in obtaining the dispersion curves of a coaxial waveguide loaded with a radially inhomogeneous dielectric. The utility of this technique is tested by comparing results with known analytical solutions. The method is also used to find the dispersion curves of a coaxial waveguide loaded with a radially Gaussian-distributed plasma.

The theory underlying the measurement of dielectric constants and power Iactors, by means of resonant lengths of coaxial transmission line, is developed, apparatus used for such measurements is illustrated and the measurement routine described. A table of typical results is appended together withan “X tan X” table for aid in the calculations.

Microwave and photometric techniques are used to study the temporal and spatial behavior of a transient microwave‐generated air plasma sheath in a coaxial transmission line. In particular, breakdown times, stabilization times, and thickness of the ionized sheath are investigated at different pressures and generating signal amplitudes.

A method for subnanosecond pulse measurements of I‐V characteristics is described. The sample is mounted at the end of a transmission line and the incident and reflected pulse is observed. In this way the sample resistance is compared with the known impedance of the coaxial transmission line and no current measuring series resistance is needed. Short pulse risetimes (170 psec) are obtained and difficulties which arise from the current measuring resistor, like temperature dependence and nonlinearity at high currents, do not obscure the measurements.

In a system where a number of transmission lines are fed from a common source, the phase relationship at the far end of the lines is determined by the electrical length of the transmission lines. This length is a function of the physical length and the dielectric constant of the line. Any variation in the dielectric constant or the physical length of the transmission line will cause a change in the electrical length and result in changed phase relationship at the far end of the line.

Simple mathematical models are developed to predict the onset of microwave breakdown in air-filled coaxial transmission lines and rectangular waveguides.

An instrument is described with which the relative permittivity and loss of disc samples of dielectric materials may be measured over the frequency range 100?300 Mc/s. The measuring cavity is essentially a short-circuited coaxial transmission line, terminated by the sample capacitance. The line length is adjustable, so that each sample may be measured at a number of different frequencies. All measurements are based upon audio-frequency calibrations of the measuring capacitors, and the design allows these to be used with only small corrections at 300 Mc/s. The corrections are analysed, and a comparison is made of different methods used for the excitation of measuring cavities. The accuracy is estimated to be ±1% in relative permittivity, and ±1?% ±0.00002 in tan ?.

Ever since the early 1940s, resonant arrays have gradually been replaced by rhombic aerials in the h.f. fixed services, for operational and economic reasons. Over the past decade, a growing awareness of the importance of the lower-order propagation modes has led to the erection of larger and higher rhombic aerials, with encouraging results. An assessment is made of the performance limits of large rhombic aerials, and it is concluded that there is scope for further improvement. The use of rhombic-type arrays, giving enhanced gain and lower subsidiary responses, is advocated. Some special considerations which apply to rhombic receiving aerials are discussed, and performance is compared to that of the sloping-V aerial. The relative merits of open-wire and coaxial transmission lines are examined, and the conclusion is reached that, from the economic view point, the former are more suitable for conveying h.f. power over the longer distances. There are, however, several reasons for preferring coaxial feeders for power distribution within the station, and the newly-developed wideband transformers permit the desirable features of both types to be utilized. Some of the switching systems which are now being used to provide the flexibility of interconnection between transmitters and aerials are also described. The aerial distribution arrangements at receiving stations and the design considerations which determine the choice between passive and active schemes are discussed. At most sites in the United Kingdom, aerial distribution amplifiers need not be used if only a few outlets are required from each aerial.