@vigneshs 

Hi,

The two 4G antennas are probably there for 2x2 MIMO (two streams of data). My guess is that the SMA port where you saw the improvement in signal strength with your new antenna is probably the main connector and the other one the secondary. MIMO is not used by the 4G modem all the time. It will switch it on or off (i.e. use the second stream or not use it) depending on various criteria.

By the way, I would say that it probably makes no sense to replace just one of the antennas. It may even confuse the modem electronics with regards to the use of 2x2 MIMO.

@woozle I'm not sure why MIMO would not use both antennas together. The core idea behind the technology is to transmit the same data over multiple antennas simultaneously. Are there any differences between the 2 antennas internally in MR200?

Regarding using 2 antennas, I'll try your suggestion. Thanks.

@vigneshs 

2x2 MIMO does not mean that the same data is transferred over two antennas simultaneously. The technology is meant to multiply the data throughput. The two data streams will be transferring different data.

For example, if a certain wireless system had a throughput of 100 Mbps using one antenna (1x1), then in a 2x2 MIMO setup it would theoretically be able to achieve a throughput of 200 Mbps, in a 3x3 MIMO setup 300 Mbps and so on.

I am not an expert on 4G technology, but one reason for your router only using one antenna could be that the cell tower you are connecting to is only assigning one antenna per user, due to capacity limitations or for other reasons. In large cities you should be more likely to receive multiple data streams than in a rural location.