To send a radio beam in a truly straight line across the Atlantic would need incredibly high masts; as it was Marconi had trouble building a mast 60 metres high for his first transatlantic transmission. In the end, he was able to 'bounce' his signals off the electromagnetic layers of the atmosphere. But this only works for certain wavelengths - and would be impossible on the frequencies used for TV signals, which are not reflected back to earth under normal conditions.
The way around this is to bounce the signals in a more organised way, by using satellites as mirrors out in space. The satellites take in the narrowly beamed signal and then direct it back to Earth - so that anyone with a dish and suitable receiver in the satellite's coverage 'footprint' can receive it.