"Friis equation and antenna effective area" article has been uploaded to the RF Design Guide page

One of the misconceptions in radio is how high frequency radio waves travel compared to low frequency radio waves. Our own intuition tends to suggest lower frequencies travel further - but this has no basis in reality.

Many sources do not sufficiently explain the derivation of the Friis formula, leaving it up to the intuition of viewer to fill in the blanks. Unfortunately, this is how such misconception arises when it comes to differences between high and low frequencies used for communication.

This article attempts to explain physically how radio waves propagate in free space, then using that as a basis to derive the Friis formula.