Millimetric waveguide systems

Abstract

The propagation of electromagnetic waves in hollow conducting tubes (waveguides) is reviewed and the properties of the low-loss mode are considered. The practical relization of a trunk digital transmission system employing the low-loss mode has been achieved in a Post Office field trial over a route length of 14 km: the system has a potential capacity equivalent to 500000 telephone circuits or three hundred 625-line television channels in each direction of transmission. The design and installation of the waveguide used for the field trial are described, and the results of transmission tests over the frequency band 32-110 GHz are presented. The wide frequency bandwidth available for transmission is subdivided into channels using appropriate filters, each channel providing a digital capacity of 500 Mbit/s. The carrier associated with each channel must be modulated by the digital signals before transmission, amplified and demodulated after transmission along one repeater section, and distortion removed from the digital signals ready for transmission over the next repeater section; techniques for carrying out these operations are outlined. Eight channels were fully equipped and the results of tests on three of the channels are given. Digital colour television transmission has been successfully demonstrated over four of the channels connected in tandem thereby simulating a 57 km route.