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How to compare SISO/MIMO and linear/X-pol gain?

madbilly

Casual Member
Hi everyone,

Another question that I'm trying to work out the answer to: when comparing antenna specs/datasheets, can I consider that 2x2 MIMO gain is effectively twice the SISO gain, if the MIMO antennas are linearly aligned/polarised? Similarly would 4x4 MIMO be 4x SISO gain? (I know that dB is log-scale so 2x6dB is 9dB, I think?)

How about if the MIMO antenna is cross-polarised? Does the max gain of two 6dB cross-polarised antenna that are 90 perpendicular to one another equal 6dB x cos(45) (4.5dB for one antenna) + 3dB (doubling by adding the second antenna) = 7.5dB? That's if the wave is between the two, oriented 45 degrees to each antenna; if the wave is aligned with one antenna and therefore not at all aligned with the other then the max gain would be 6dB.

So, potentially a linearly-aligned MIMO antenna can give much more gain, but only if it's well aligned. A X-Pol MIMO antenna has a lower potential max gain but can more reliably pick up a signal in any orientation?

This finally leads me to ask - do datasheets for MIMO antennas show the max gain of all antenna combined or of each antenna?

Cheers :)
 
All the below is imho (not a professional).

The advertised gains are for all elements/antennae inside a unit usually.
The overall gain of a 2x2 mimo is not a double of the siso, that may only be so in theory, who knows. I reckon intuitively it's somewhere between 1x and 1.5x.
Combining 4 siso antennas could give you good 4x4 mimo, depending on quality and orientation.

Cross-polarised antennas are better at picking up a good signal.
 
Hi Lucian,
Thanks for the explanation. After looking at a few more datasheets that makes sense, I think I understand more about what they're telling me now.
Cheers :)
 
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