Wifi Router

More antennas are better. 

The problem is it usually isn't the routers antenna's being the bottleneck or causing issues. 

Its your own devices internal antenna. 

Most phones, tablets, pc's, etc are all 1x1 or 2x2 antenna devices. 

And their internal broadcast power is usually less capable than the routers broadcast power. 

A typical (not all) phone broadcasts a 15mW versus your router can transmit at up to 1W of power (depending on channel/band).

Its why sometimes its beneficial to turn down the broadcast power on a router and add extra access points. 

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emmajan123 wrote:

Hello, I want to know like some people say 3 antennas work better than 2.

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Better for what?

Range? Speed? Aesthetics?

Then there is the size of the antennas. Two big might beat three small, depending on what interests you.