Fresnel Zone Clearance Requirements for Circular Polarized RF Links vs Linear Polarized

Hi, some questions on Fresnel zones and multipath interference. I have read in various articles that circular-polarized (CP) transmissions are "more immune" to multipath interference than linear polarized signals. As I understand it, this is because a reflected CP signal will have the opposite polarization direction. In other words, when an LHCP signal is reflected, it becomes RHCP, which is not received by the antennas in the system, as they are optimized for LHCP.

How does this relate to Fresnel zones and LOS (Line of Sight) transmission? A typical requirement for a RF link is that the 1st Fresnel zone is at a minimum 60% unobstructed. Does this apply even for CP signals? I would think that any multipath signals in a CP system would be polarized orthogonally to the receiver, and therefore, would not effect the quality of transmission. Would the link work as long as there is an unobstructed LOS? Is there a different standard for the Fresnel Zones in a CP system as compared to a linear system?


Also, what is the reason that the equations for Fresnel Zone do not include anything about antenna beam width? One would think that a very narrow beam width would keep the level of any reflected out of phase signals low enough to not matter. Let me know if I can be more descriptive for either of these questions. Thank You

The Fresnel zone is made up of multiple zones and would be a 3D elliptical region between the transmit and the receive antenna. As any interference or obstruction in the LOS can result in a loss of signal. In general, the first Fresnel zone is  at least 60% to ensure the highest performance.

Is there a way to quantify how much more resistant Circular Polarized transmission is to multipath interference vs linear polarized? I understand the general rule of 60%, but I guess I am trying to dig further into the assumptions that allow this generalization to be made.