Microwave receiver antenna height

I want to do a simulation of fixed-service microwave links and I want to know how antenna heights above ground level (AGL) are determined on the receiving side.

For instance, if the transmitter antenna AGL height is 50 meters, then at a particular receiving location, will the receiver antenna AGL be such that, 1) based on the terrain elevation at the receiving location and 2) the tilt of the transmitter antenna, a visual line of sight between the transmitter antenna and the receiver antenna gets created?

That is to say, to compute a receiving side antenna AGL, should I look at the terrain elevation at the receiving location, the tilt of the transmitter antenna, and the transmitter-receiver distance (with earth curvature: the great circle distance would be selected as distance) to choose the receiver antenna AGL to create a visual line of sight geometrically?

• You need a clear line of sight. How you work that out is up to you and basic geometry. Note that it is quite likely that your receiver will also be used as a transmitter. Commented Jan 10, 2023 at 16:54
• @Andyaka: that's the answer, you should make it so. If you have any handy, links to handbook solutions would be nice. Commented Jan 10, 2023 at 17:40
• Note that this is an easy problem in principle -- just establish a clear line of sight. The difficulty is in actually finding a home for the antennas, including whatever towers they may need to go on, while satisfying whatever regulations apply. Commented Jan 10, 2023 at 17:42

1 Answer

The simple geometric formula is well described in this thread on Stack Exchange Mathematics. But this assumes a perfectly smooth round Earth and ignores refraction and scattering effects.

Unless you're transmitting over very flat terrain, or water, you need a topographic profile to find the highest point that must be cleared. If tall trees are involved, you'd need to add clearance to stay above those.

To be even more precise, you would take into effect that the microwave beam is actually refracted, or bent, due to the variation of density of air and moisture in the atmosphere with height. And this factor can change with weather conditions.

Bottom line -- allow a safety margin for your path calculations if you want a reliable link.