Point to point link design from the first clearance check to a full path on terrain: Fresnel zones, the link budget, rain fade and availability.
The discipline
A point to point microwave link looks simple on paper: two sites, a clear line of sight, a frequency and an antenna at each end. Getting from there to a link that meets its availability target means accounting for terrain, Fresnel zone clearance, atmospheric absorption, rain, multipath fading and the links already licensed around you. Skip one and the link either underperforms on the day or fails coordination at licensing.
Clearance comes first. Radio energy travels as an ellipsoid around the direct ray, not a pencil beam, and industry practice keeps at least 60 per cent of the first Fresnel zone clear of obstructions. Refraction bends the path, so clearance is checked at an effective earth radius factor k, with the earth bulge between the two ends added to the terrain.
Then the budget. Free space path loss is the floor every other loss sits on, and fade margin is the reserve that rides out the rest. On long paths below about 10 GHz multipath fading usually sets that margin; above that, rain takes over, and the ITU-R chain of rain rate, specific attenuation and path scaling turns a rain climate into an attenuation you can design against.
The tools below start with the quick checks you can run from a site survey and finish with the full path design on terrain.
The workflow
Line of sight is not enough. The calculator gives the first, second and third Fresnel zone radii along the path, checks each obstacle against the 60 per cent first zone rule, and adds the earth bulge at the k factor you choose.
Do it withFresnel Zone Calculator Free Open the tool →Account for every dB between the transmitter and the receiver: EIRP, path loss, received power, noise floor, carrier to noise and fade margin, with presets for microwave, land mobile, WiFi, LTE and satellite links.
Do it withLink Budget Calculator Free Open the tool →At the higher microwave bands rain sets the fade margin. The calculator shows each step of the ITU-R chain (P.838 specific attenuation, P.530 path scaling, P.840 cloud and P.676 gases) with a Bureau of Meteorology site lookup for Australian paths.
Do it withRain Fade Calculator Free Open the tool →Build the link on a terrain profile and run it to ITU-R P.530-19: Fresnel clearance on the real ground, rain, gas, cloud and multipath fading, adaptive modulation and diversity, antenna patterns and availability, with the provenance of every number. It also plans point to multipoint sectors with a budget per subscriber.
Do it withLink Planner Pro Open the tool →Availability figures are statistical predictions from ITU-R climate data. Confirm the path with a site survey before committing to hardware.
The rest of the kit
From other disciplines
Further reading
Free tools are free on a Standard account, with no time limit. Pro tools are included in the 14-day trial on every new account. No credit card.
