Closed form solutions for the evaluation of the wave and natural parameters of inhomogeneous cable configurations where skin- and proximity-effects are present rarely exist. In most cases such parameters can only be retrieved from measurement experiments or by resorting to numerical methods. In this short paper we present the theoretical foundations of a novel measurement principle, as well as specific formulae for the determination of the parameters of a shielded bifilar line, avoiding the end-effects that usually arise when cables are tested using short- and open-circuit terminations. Copyright © 2010 John Wiley & Sons, Ltd.

A theoretical contribution for retrieving the wave and natural parameters of shielded pair cables

The shielded cable with close inner conductors is different from the conventional local cable and can be applied to directional couplers. In this paper, for the purpose of obtaining tight coupling, we investigated the cable in which two inner conductors are very close. In particular, we consider the finishing with very fine conductors for small power application. In this case, it is necessary to use a second dielectric in order to maintain the space between the inner conductors, resulting in an inhomogeneous media. For the solution of such a shielded cable pair by quasi-TEM mode approximation, we use the method of conformal mapping. Also, the measurements of the cable constants and the restrictions of a directional coupler by TEM approximation are described. The approximate equations obtained are applicable to the design of a cable with tight coupling below about 10 dB and the trial production of 3 dB- and 5 dB-cables was proved to be satisfactory. The directional couplers using these cables are possible in practice and we expect to see their application in the VHF and UHF bands.

Teruaki Arakawa

Papers

An analysis of shielded pair cable for tight coupling by conformal mapping and its application to directional couplers