Is the Horn Front-To-Back ratio a myth?

[And]

Why Mikrotik SXT and other antennas front to back ratio is better then horn or similar 30-35 (...horn high-frequency currents do not have time to pass into the electric field and flow to the external surface of the horn and create side lobes, but if in case they have a ribbed inside, it helps a bit)?

Edited July 15, 2021 by And
Correct image, Correct topic

[And]

Carrier Class horn HG3-CC-A60-V2 Front-to-Back Ratio only 27 dB

Its inside is not ribbed?
Does any RF horn have a ribbed inside or is it too expensive?

[Tom]

The Symmetrical horns do have corrugations inside, from the Asymmetrical ones only the 30 degree one does, the 60 and 90 do not.

How much FtB ratio is enough? And why do you think it is important?

[And]

I find it strange that antennas with such an FBI rating can be assigned a class carrier.
The question of why this is important also seems strange, but perhaps it was meant differently.

Smaller FBI, more noise. It probably doesn't affect that much if everyone on the mast is horn, but in the case of a hybrid, it makes more noise than if there were no horn. Noise is the biggest invisible enemy.

Edited July 15, 2021 by And
added text

[Tom]

11 hours ago, And said:

I find it strange that antennas with such an FBI rating can be assigned a class carrier.
The question of why this is important also seems strange, but perhaps it was meant differently.

Smaller FBI, more noise. It probably doesn't affect that much if everyone on the mast is horn, but in the case of a hybrid, it makes more noise than if there were no horn. Noise is the biggest invisible enemy.

Right, the higher FtB ratio the less noise. But, FtB ratio quantifies only the backlobe - one side lobe out of many antennas used in WISP industry typically have and all that at one frequency and from a single polar plot.. What about the rest of the radiation pattern? The rest of the sidelobes are much substantial than just backlobe by itself. 

This is exactly why FtB ratio is practically useless (in other words useful in very few instances). We believe Beam Efficiency (BE) is way more comprehensive and reliable measure of noise suppression capability of antennas. More over, we extended its definition to an average number over the whole antenna bandwidth and both polarizations, which makes it super robust noise suppression measure. 

BE is great because it gives you a simple numerical value from 0 to 100%. The higher the BE is the better an antenna suppresses noise - check the BE of the most common antenna types here..

We also have a full webinar on BE if you want deeper explanation and have a little time - here..

What do you think about BE vs FtB?

[And]

I think BE is more for CPE, but the FTB is a mast for colocation.  "The fish is blowing from the head."

I also think that the criteria for awarding a Carrier class need to be reviewed (for example P2P SAF FreeMile Parabolic Frequency: 24.05 - 24.25 GHz, Gain: 45.1 dBi (high-band), Half power beamwidth: 1.0°, Cross-polar discrimination: 30dB, Front-to-back ratio: 70dB). Of course PTMP will have a different FTB ratio, but not 27 dB.

 

[Tom]

BE is important for both AP and CPE, but more so for AP (from the angle of a network as a whole), since AP is the device to which all the CPEs are connected. So if the AP radio is seeing a lot of noise, all CPEs suffer. Where as if only one CPE sees noise, it's only that one user that sees the effect..

In my opinion BE says much more about colocation capability than FTB ratio - one side lobe (back lobe) simply cannot be more important than all the other side lobes combined.