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)
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