WT4 millimeter waveguide system: Field evaluation test — transmission medium achievements

A 14 km length of WT4 millimeter waveguide, designed to operate from 40 to 110 GHz, was installed in northern New Jersey and tested during the AT&T WT4 field evaluation test. The waveguide transmission medium has characteristics and requirements which are quite different from those for existing Bell System facilities, such as coaxial cable or microwave radio. Thus, a significant part of the field evaluation test effort was devoted to the installation and characterization of the waveguide transmission medium. The most significant transmission medium achievements of the field test were: (I) demonstration of the practicality of sheath and waveguide installation with standard construction methods, (ii) low transmission medium losses which allow a repeater spacing in excess of 50 km, (iii) theoretical prediction of electrical losses from mechanical measurements of waveguide curvatures, and (iv) development of an experience and data base from which losses for future waveguide routes were projected. The measured loss of the 14-km-long field evaluation test waveguide line was approximately 1 dB/km or less across the 70 GHz band–the lowest losses for a waveguide system yet reported in the world–which confirms that the installation methods used result in curvatures acceptable for a commercial WT4 system.