Equatorial Atmosphere Radar (EAR) is a large Doppler radar built for atmospheric observation at the equator in West Sumatra, Indonesia (0.20S, 100.32E, 865m MSL). The construction was completed in March 2001, with collaboration between RISH, Kyoto University and the National Institute of Aeronautics and Space of Indonesia (LAPAN) of Indonesia. The EAR has a circular antenna array of approximately 110 m in diameter, which consists of 560 three-element Yagis. It is an active phased array system with each Yagi driven by a solid-state transceiver module. This system configuration makes it possible to direct the antenna beam by electronic control up to 5000 times per second. The EAR transmits an intense radio wave of 47 MHz to the sky and receives extremely weak echoes scattered back by atmospheric turbulence. It can observe winds and turbulence in the altitude range from 2 km to 20 km (troposphere and lower stratosphere). It can also observe echoes from ionospheric irregularities at heights more than 80 km.