Crosstalk Between Coaxial Transmission Lines

C O A X I A L line consists of an outer conducting tube which envelops a centrally disposed inner conductor. The circuit is formed between the inner surface of the outer conductor and the outer surface of the inner conductor. Since any kind of high-frequency external interference tends to concentrate on the outer surface of the outer conductor and the transmitted current on the inner surface of the outer circuit, the outer conductor serves also as a shield, the shielding effect being more effective the higher the frequency. D u e to this very substantial shielding at high frequencies, this type of circuit has been a matter of increased interest for use as a connector 144 CROSSTALK BETWEEN COAXIAL TRANSMISSION LINES 145 between radio transmitting or receiving apparatus and antennae, as well as a wide frequency band transmitting medium for long distance multiplex telephony or television. It has been a subject of discussion in several articles published in this country and abroad.* The purpose of this paper is to dwell at some length on the shielding characteristics of a structure exposed to interference from a similar structure placed in close proximity. Such interference is usually referred to as crosstalk between two adjacent circuits, so that the purpose of this paper is a study of crosstalk between two coaxial circuits. In what follows we shall give an account of the theory of crosstalk, the results of experimental studies, and application of these to long lines employing coaxial conductors.