Abstract
A theoretical treatment for studying the propagation and radiation characteristics of leaky cables is described. The continuously slotted coaxial cable is studied in free space, both in electrostatic conditions and at VHF. Results from the former analysis were obtained by the use of a conformal transformation technique; they refer mainly to the distribution of energy inside and outside the coaxial structure and to the capacitance, the value of which was found to be in very good agreement with measurements. For the latter a modal analysis was carried out concurrently with a discussion on the optimum number of terms for the series, describing the fields and the slot functions; the results showed that a quasi-TEM mode, slow wave, had conditions to propagate in such structure. A loose braid coaxial cable is also studied, both in free space and above a conductive ground plane. A discussion on two possible interpretations for the sign of the surface transfer impedance is presented and related to two different modes of propagation. The results from the study of the cable over a perfectly conductive ground plane indicate the possible existance of two uncoupled modes, a slow and a fast wave, propagating simultaneously along the structure. The possible causes of the 'standing waves' are discussed and two approaches to overcome their adverse effects on communication are indicated. Finally, conclusions are taken with special emphasis bn establishing general guide-lines relevant to the design of a system.