Determination of Antenna Height for Protection Against Microwave Diffraction Fading

The wide variations in refractive index gradients that may be encountered for nominally line‐of‐sight 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‐interference fading. The diversity design procedures, (b) above, have 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.