Signatures are defined for both minimum and nonminimum phase fading. The signature is defined as the locus of notch depth required to produce a specific BER when the flat fade margin (FFM) and relative delay are fixed. The ability of the radio to withstand a notch or its slope within its bandwidth is defined the area contained by the locus. The receiver signature is important when the bandwidth is higher (with increased capacity) and selective fading becomes important. However, the concept of selective fading becomes relevant at low frequencies, high capacity and over long hops. The outage probability due to frequency selective fading can be calculated as Ps=2.15n Tr,M + WNM X 10 BNM/20 Tr.NM T m 2 (3.51) (3.52) Transmission Network Planning and Optimisation f-fo (MHz) Figure 3.52 Signature results (laboratory simulated) where W = signature width (GHz) Bx = signature depth (dB) Tr,x = reference delay (ns) used to obtain the signature, with x denoting either the minimum (M) or the nonminimum ( NM) phase fading. The amplitude and phase of the signal bening reflected from the surface is also dependent on the surface type. The smoother the surface, the more severe the effect of the indirect signal on the direct signal will be. The maximum damage is caused when the amplitude of the direct and the indirect signal is the same while they are in anti-phase. The conductivity and permittivity of the surface affect the amplitude of the reflected signal and depend on the polarisation and frequency of operation. The roughness factor of the surface determines the amount of signal that will be reflected from the surface. This is given as (3.53) where S = standard deviation of the surface height about a local mean (within the FFZ) 2 = wavelength of the signal Q = grazing angle The surfaces with g < 0.3 are considered to be smooth. The higher the values of g, the smoother the surface will be, thus resulting in maximum reflection of power. Hence, microwave signals passing over water bodies or a paddy field should be avoidOed as the