Using a 4G antenna indoors
If you've read the previous section on 4G antennas you'll be aware that poor 4G speeds in most suburban and built up areas tends to be caused by nearby buildings, trees, and your building itself. What this means is that to see a significant improvement to your 4G connection an antenna really needs to be placed outside or on the roof where the impact of your building and other nearby obstructions is minimised.
Of course if you're like many (perhaps you're renting) and don't have any choice in the matter, or you're picking up some 4G service inside but just need to boost it up a bit, an indoor antenna can work quite well. The key to success with a 4G antenna is location.
As radio waves cannot penetrate well through thick walls or metal, signal often flows into the building through doors and windows. It reaches around corners and into rooms by reflecting off just about every surface, creating an extreme multipath environment. Because inbound radio waves will be approaching from just about every possible angle the best performing antenna for this situation is often a 0 dBi antenna (i.e. one that can receive from every spherical direction) such as the one that's already in your modem. This means that in order to use an indoor antenna successfully you need to locate it in the source of the signal - i.e. in the window or doorway.
If your equipment does not permit relocating the antenna, the only method of improving performance is moving from a standard grade antenna to one with high electrical efficiency. Just like mechanical efficiency, an electrical component like an antenna can only theoretically be 100% efficient (see: first law of thermodynamics). Due to mismatch and material losses a good quality antenna will radiate 50 to 60% of power supplied to it - i.e. -3 dB average gain (integrated over 4*π). Low cost antennas often radiate as low as 10%. For high efficiency antennas look no further than those manufactured by Taoglas, and many Telco OEM designs.