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My Wifi router claims to provide bit rate upto 300Mbps and support 802.11 b/g/n. But 802.11n standard requires using 4 streams(4x4 MIMO technique) using 4 different antennas. Mine has only 2 antennas. It should have been capable of providing only 2x72 Mbps(54Mbps x 4/3 (taken from 802.11g) times the number of antennas). How is my router claiming to provide a speed that can only be achieved using 4 antennas while it has only 2 antennas. (I am under the assumption that each antenna caters to adding 1 spatial path)

vai
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    There is a handy table on [Wikipedia](https://en.wikipedia.org/wiki/IEEE_802.11n-2009) showing the different configurations and the resulting data rates. There is one config with 2 streams resulting in 300Mbps. – Eugene Sh. Nov 10 '17 at 16:08
  • The standard supports up to 4x4 MIMO, but it does not require that devices support 4x4 MIMO. Don't forget about the wider 40 MHz channels that can go a lot faster than 54 Mbps. – alex.forencich Nov 18 '17 at 07:22

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Multiple antennas on routers are used for beam-forming.

Each antenna can handle whatever standards the router supports, but the more antennas the router has the better job it can do to form directional capability to reach each device that is connected.

I suggest you do some searches on Amazon and Google and read the specs for different routers that have various antenna configurations - they will describe this capability so they can justify higher prices for routers with more antennas.

Take a look at the Wikipedia article mentioned in comments to begin.

The more antennas the router has the more efficiently it can communicate due to the virtual beams, which can result in higher speeds.

It is not because it uses different 802.11 standards on each antenna.

SDsolar
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Your router will be able to achieve 300 Mbps using 2x2 MIMO coupled with channel bandwidth of 40 MHz (ie. by using two streams each occupying same 40 MHz of channel bandwidth).

802.11g gives peak speed of 54 Mbps with 20 Mhz of Bandwidth. In advancement to 802.11n, speed is improved to 72.2 Mbps (with single stream, 20 MHz channel Bandwidth) by improvement in factors such as increased number of data subcarriers, reduction in guard interval etc. When 40 Mhz channel is used, the data capacity is increased to 150 Mbps (which is little more than 72.2 x 2). This is because the wider 40MHz channel is utilized more efficiently compared to 20 MHz channel. And when 2 special streams are used on the same 40 Mhz channel using MIMO technology, each stream carries 150 Mbps and thus the speed goes to 300Mbps.

Note 1: Number of spatial streams a router/AP can support is not evident from the number of antennae connected to it. It is usually written on router specifications. Thus an AP can have 3 antennae but can support only 2x2 MIMO (2 spatial streams).

Note 2: It has to do nothing with beamforming technology as mentioned in other answers. 802.11n specification mentions about the beamforming capabilities in its documentation but it is almost never implemented in commercial 802.11n chipsets due to high complexity. Beamforming and MIMO concept are technologically two different things.

Ashutosh
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