Loop antenna
Small loops have a poor efficiency and are mainly used as receiving antennas at low frequencies. Except for car radios, almost every AM broadcast receiver sold  has such an antenna built in or directly attached to it. These antennas are also used for radio direction finding.  In amateur radio, loop antennas can be used where larger antennas would be inconvenient, unsightly, or banned because of size. Loop antennas are relatively easy to build.