Determination of Antenna Height for Protection Against Microwave Diffraction Fading

Abstract

The wide variations in refractive index gradients that may be encountered ·for nominally line-ofsight microwave maritime paths can cause severe fading. A common type is known as k-type fading which includes phase-interference fading and also diffraction fading as the refractive index gradient varies over a wide range. Lewin (1962) was the first to provide an engineering design procedure that roughly approximated: (a), the required terminal antenna heights to reduce diffraction fading, and (b), the required diversity separations (frequency or space) to provide a dynamic reduction of phase-inter· ference fading. The diversity design procedures, (b) above,.bave since been derived in a more accurate manner although they presuppose that item (a) has been provided for. The present paper meets this requirement. It provides a more accurate design procedure for determining the requirements, (a) above, to reduce diffraction fading. As an aid for the procedure, a new computer-derived curve is presented for the attenuation by a spherical earth at grazing conditions.