What is size of the Fresnel Zone for the 60 GHz MetroLinq radio?

What is size of the Fresnel Zone for the 60 GHz MetroLinq radio?

What is the Fresnel Zone for the 60 GHz MetroLinq radio?

See chart below.  One advantage of mm wave technology is very small Fresnel zones.  Fresnel zone size is a function of frequency and distance.  As frequency increases, the Fresnel size decreases and as distance increases, the Fresnel zone increases.

The Fresnel Zone represents a series of regions in which surfaces will cause a reflected wave, phase shifted by some amount, to constructively or destructively interfere with the desired Line-Of-Sight (LOS) signal at the receiver.  These concentric ellipsoidal regions  (F1, F2, F3, etc)  of radius R -- the first (F1) having the smallest R -- are centered on the direct transmission path between two radios (Figure 1).  The total phase difference between the line of sight signal and the reflected signal is determined by factors such as the shape and properties of the obstruction as well as the polarization of the incident wave.  Additionally, obstructions can cause diffraction and other undesirable effects. Even in systems with very directional antenna patterns (such as MetroLinq), If a significant portion of F1 is obstructed, the signal at the receiving antenna can be greatly attenuated.

 A general rule of thumb is that to avoid the significant signal blockage, diffraction or multi-path attenuation (for your link to behave as LOS), you need at least 60% of F1 clear of  obstructions, where "60% of F1" is defined as a narrower ellipsoid with a radius that is 60% of the radius of F1.


Figure 1: Fresnel Zone (not to scale)

The radius of F1 is dependent upon the frequency and distance of the link, and therefore it is calculated for 60 GHz at multiple distances below:
 

Link Distance

Max. F1 Radius

kilometers

miles

meters

feet

0.1

0.1

0.4

1.2

0.2

0.1

0.5

1.6

0.3

0.2

0.6

2.0

0.4

0.2

0.7

2.3

0.5

0.3

0.8

2.6

0.6

0.4

0.9

2.8

0.7

0.4

0.9

3.1

0.8

0.5

1.0

3.3

0.9

0.6

1.1

3.5

1.0

0.6

1.1

3.7

1.1

0.7

1.2

3.8

1.2

0.7

1.2

4.0

1.3

0.8

1.3

4.2

1.4

0.9

1.3

4.3

1.5

0.9

1.4

4.5

1.6

1.0

1.4

4.6