With any antenna, the apparent increase in signal is not an amplification of signal, but it is the act of redistribution of available Radio Frequency (RF) signal into a preferred direction. So basically, antennas only divert, direct, or concentrate radio energy in some direction, they don’t create it.
The increase in signal using an antenna is called gain and is measured in dBi.
As new RF signal is not generated, the stronger signal is achieved at the expense of most other directions.
Some people think that a higher gain antenna will give them the strongest signal and highest quality connection. This is true in some cases, but in certain applications too much gain can be a bad thing.
Moreover, you can be looking at two different antennas that have the same gain according to the spec sheets, but one of them can have the potential to perform better than the other. An understanding of where and how the antenna will be deployed is key to help determine which environmental parameters are important and in turn which antenna would suit you best.
Another thing that you have to be aware of is that walls or objects can weaken the signal. In addition, certain radios work better transmitting more power and using smaller antenna while others like to transmit less power but use a larger antenna. Having a bigger antenna does not always increase the usability of the signal. It may increase the total signal strength but it also can increase the noise in the signal.
Poynting 4G-XPOL-A0001 Cross Polarised 4G Omni LTE Antenna