A large MST radar for observing backscattering from refractive index fluctuations in the middle and upper atmosphere is now under design in Japan. The proposed system is a pulse-modulated monostatic radar, working at a frequency near 48 MHz. The configuration will be quite different from the existing MST/ST radars. A quasi-square array with an aperture of 104 m2 is composed of 456 Yagi antennas, each of which is provided with a low-power amplifier. A peak output power of more than 1 MW is envisaged to be generated when the whole system is coherently activated. In this system a phase shift is obtainable at a low power level by variable phase shifters controlled by electronic means, which enable rapid and continuous scanning of the antenna. The whole system is monitored and controlled by a microcomputer network.