Amateur radio/Unidirectional propagation antenna

A unidirectional propagation antenna is an antenna that has a propagation pattern in only one direction. Unidirectional propagation antenna are good for communicating with someone or something when you know where the station is. The following are examples of these.

Radar antennas
Radar antennas are type of unidirectional propagation antenna.

Yagi-Uda antennas
This kind of antenna is also a unidirectional propagation antenna.

Satellite dishes
A satellite dish is a unidirectional propagation antenna that we see a lot. They are usually used to communicate with satellites hence the name "satellite dish"