Abstract
The radiation from the open-circuited end of an external dielectric coated waveguide can be controlled by varying the size of the guide, the thickness and / or the dielectric constant of the coating. A new type of aerial designed around this principle is given the name "Surface Wave Aerial", and radiation pattern measurements are used to confirm the theory underlying this type of radiator. According to its mode of operation it belongs to the category of end-fire aerials which are briefly review- ed to show that "Surface Wave Aerials" occupy a place in their own right amongst the many possible arrangements that utilise the end-fire effect to produce a directional radiation pattern. The theory of the "Surface Wave Aerial" is developed in detail; a necessary preliminary step being a full theoretical analysis of the properties of the first order cylindrical surface wave. It is shown that a dielectric coated cylinder which is approximately a wavelength in circumference can act as a waveguide for higher order surface waves, of which the first order is an example. The "Characteristic Equation" is determined for the general case from which in turn the cut-off frequency and the propagation constant are derived. Two specific cases are evaluated numerically and the results are used to calculate the polar diagrams of Surface Wave Aerials operating at 150 Mc/s and at 9000 Mc/s respectively. Experimental confirmation at 150 Mc/s is obtained by means of semi-automatic polar diagram plotting equipment which is described in detail. The initial choice of frequency, governed by available high frequency generators, did not permit the full exploration of the properties of the 1st order surface wave and a short section is devoted to, experiments which were carried out at 9000 Mc/s. The propagation constant was measured directly and the behaviour of very long aerials, approximately 20 wavelength long, was studied. In conclusion an outline of future work is given.