Propagation impairments due to man-made structures on digital microwave links

The growth of cities has promoted the concentration of microwave radio communication links and the dimensional enlargement of man-made structures such as office buildings, billboards, towers, power transmission lines, etc. This results in the possibility of close arrangement or intersection of man-made structures and microwave propagation paths for radio communications. If those structures are within or close to radio paths, they would probably screen (or diffract), reflect, or scatter the microwaves and interfere with communications. Above all, reflection or scattering would cause intersymbol interference on digital microwave communications, while diffraction, assuming a man-made structure as an infinitely thin wave-absorbing plate, could cause only the loss of received power, or diffraction loss. The paper focuses on the effects of interfering waves reflected by building walls and those scattered by conductors on digital microwave communications. The methods for estimating propagation impairments due to reflection and scattering are presented in terms of equivalent carrier-to-noise (C/N) degradation. The degradation of cross-polarization discrimination (XPD) due to scattering is also discussed.