3.1 Design Process Flowchart

Microwave link design is a methodical, systematic, and sometimes lengthy process that includes the following main activities:

• Loss/attenuation calculations

• Fading and fade margins calculations

• Frequency planning and interference calculations

• Quality and availability calculations

A preliminary fade margin is a result of the loss/attenuation calculations and is used for preliminary fade predictions in the fading calculation. If interference is present in the frequency-planning calculation, then the threshold degradation is included in the fade margin. The updated fade margin will become the effective fade margin used in the fading predictions. The results of the loss/attenuation and fading calculations will form the necessary input to the quality and availability calculations. The whole process is iterative and may go through many redesign phases before the required quality and availability are achieved (see Fig. 3.1).

Figure 3.1: Microwave link design process.

3.2 The Loss/Attenuation Calculations

The loss/attenuation calculation is composed of three main contributions: propagation, branching, and "miscellaneous" (or other) losses. The propagation contribution comes from the losses due to the Earth's atmosphere and terrain e.g., free-space as well as gas, precipitation (mainly rain), ground reflection, and obstacles. The branching contribution comes from the hardware required to deliver the transmitter/receiver output to the antenna e.g, waveguides as well as splitters and attenuators. The "miscellaneous" contribution has a somewhat unpredictable and sporadic character, e.g., sandstorms as well as fog, clouds, smoke, and moving objects crossing the path. In addition, poor equipment installation and less than perfect antenna alignment (field margin) may give rise to...