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I'm traveling to Asia and using one of their fiber ISP, they give me a modem combo that have wireless router built in. It have a RTL8192ER chipset for wireless, which is 2x2 MIMO, but there's only one antenna on the PCB. I do get 300Mbps indication on some devices, however Wikipedia says it's not possible to have 2 streams on a single antenna.

So is it only capable of 1x1:1, despite of the 300Mbps indicator on some wireless clients?

I tear it down and here are 2 photos for both side of its PCB:

PCB Front PCB Back

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  • Can you perhaps provide a photo of the antenna, viewing it from both sides?
    – Daniel B
    May 8, 2017 at 8:04

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photo

I'd guess that one antenna is the bigger piece of metal, and the other antenna is a PCB antenna, judging by the RF circuitry leading to it. The 300 Mbps measured on your client is also an indicator for MIMO being used here.

(also there are 2 footprints for external antenna/U.fl connectors on the board)

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    Great catch! On the other side of PCB, the metal one is clearly grounded only on one end, so it probably really is another antenna. We still don't know if it's for Wifi though :)
    – quetzalcoatl
    May 8, 2017 at 13:45
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MIMO works by using the fact that on antennas in different places, the radio waves will arrive with a slightly different phase. And this phase difference in turn depends on the location of the sender, so if there are two senders in different locations (or one sender with two antennas), both senders can be distinguished by a receiver with two (or more) antennas.

Vice versa, by sending out radio waves with a phase difference on different antennas, you can force better reception in some places (and worse reception in others). This is also called beamforming.

So you definitely need multiple antennas to make MIMO work, because it's required by the physics MIMO is based on. Just like you need two eyes for binocular ranging (a form of three dimensional depth perception).

The clients may recognized that the chipset supports MIMO, and maybe even may try to make MIMO work if the chipset doesn't know it has only one antenna, but physically several streams just won't work.

That said, it's often not obvious where the antennas are on a PCB. One antenna could be integrated into the PCB, or the blue thing could house two antennas, or ...

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    The "blue thing" is the fiber connector and has nothing to do with wireless. It looks like there's one antenna only and the second is not connected so it can still work under perfect conditions, that's why sometimes the devices switch to 300mpbs (whether they can actually achieve that 300mbps is another matter, and with the antenna disconnected I doubt they're getting any bandwidth out of that second channel).
    – André Borie
    May 8, 2017 at 10:12
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If there is only 1 antenna its only capable of 150Mbps (assuming it can handle wide channels). Actual throughput will, off-season be less.

In order for MIMO to work multiple antennas are required on both ends so that differences in signal paths can be measured and used.

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