To put it simple, there are two ways Internet signal can reach you at the height of 35,000 feet. First is using the broadband towers sending the powerful signals to the aircraft antennas (usually located on the fuselage base — the belly of a plane).
As the aircraft moves, it automatically reconnects to the nearest tower on Earth. However if you are travelling over remote terrain for too long, there can be a lack of connectivity.
Second way of getting WiFi on planes is using satellite technology. Aircraft connects to satellites in geostationary orbit (35,786km high), and they transmit signals to Earth via receivers and transmitters. These satellites are the same used in TV, weather forecasting, and secret military operations.
Data is transmitted via an antenna that is located on the top of an aircraft and connects to the closest satellite. The Internet signal is distributed among the passengers with a router located on board.With both methods, US air companies have a better developed infrastructure than carriers in other countries. Subsequently the US carriers offer a better and often cheaper WiFi on plane than European carriers.
Although technology is developing at an impressive pace, it has still to catch up with the number of devices on board that are desperate to connect to the Internet.
When an in-flight broadband company Gogo (previously known as Aircell) launched its first WiFi service in 2008, the 3 Mbps speed was just enough for several computers on board (video streaming was blocked). However now that it's getting so popular every passenger will connect at least one device to the network. A satellite connection will offer around 12 Mbps, which is much better, however very expensive and high-maintenance.
If an even WiFi signal needs to be distributed on board of a plane, one can use the NetSpot app for a detailed coverage analysis and correct placement of access points in the aircraft.
Naturally all the advanced technologies with such high-maintenance equipment don't come cheap, especially if you add an aircraft to the equation. Antennas also increase drag, adding fuel costs to the airline’s bill.Every little expense, including maintenance and engineering will reflect on the end customer. The price on in-flight connectivity can vary from company to company, and free inflight WiFi trial is usually offered by a handful of airlines.
Make sure to check the restrictions these free WiFi services come with: some will only be available for laptops and tablets, some will only be offered on domestic flights.