Loop antennas are used mainly for reception of radio signals, navigation and in RFID technology. They are complementary to dipoles from the electromagnetic point of view

For theory see:

Orphanids, S: Electromagnetic Waves and Antennas, 2004-10, chapter 14: http://eceweb1.rutgers.edu/~orfanidi/ewa/ch17.pdf
Kraus, J.D., Marhefka, R.J.: Antennas for all applications, Mc Graw Hill 2003, chapter: Loop antennas (7)