Abstract :
Principal microwave problems encountered in the design of longrange communication systems using waveguides are discussed. The reasons for choosing as the medium of transmission the circular waveguide excited in the H01-mode are given, and means of bridging engineering difficulties are analysed in some detail. In particular, it is shown that plain metal waveguides are not suitable for long-range application, unless the waveguide run is substantially straight. Practical waveguides, however, must be able to follow ground contour and other unintentional bends¿a condition under which the performance of conventional waveguides is considerably degraded. The problem of unintentional bends is analysed in detail using perturbation calculus and the concept of surface impedance. The formulae obtained lead to design criteria for waveguides which are free from the above restrictions. A number of suitable waveguides are introduced and the proportions are chosen with the help of charts given in the paper. A circular metal waveguide coated with a thin skin of a dielectric is a possible solution. Circular anisotropic waveguides are discussed at length and, among other designs, the helical waveguide of suitable proportions is shown to be another possible solution. Numerical examples are given to illustrate the design approach and to contrast the performance of optimum designs with conventional waveguides. These examples also show that, whereas the special waveguides can be bent¿for example, to follow the ground contour¿ to a radius as small as 100 m (or even less) without causing any appreciable deterioration in their electrical performance, the conventional waveguides under similar conditions would be considerably degraded, even to the extent of being useless for practical applications.
