The Straight Flush was the NATO designation to the Soviet-built 1S91, 25kW G/H band radar, which was part of the 2K12 Kub mobile surface-to-air missile system. Equipped with a continuous wave illuminator and an optical sight, the 1S91 radar had a range of 50 miles (75 km). The Straight Flush radar (1S91) emitted radio waves in the range of radio frequencies from 6 GHz to 8 GHz in the electromagnetic spectrum. This is equal to wave lengths between 5 cm and 3.75 cm. The H band is in the SHF range of the radio spectrum.
The 1S91 mobile radar unit was composed of two radar stations: a target acquisition and distribution radar 1S11 and a continuous wave illuminator 1S31, in addition to an IFF interrogator and an optical channel. While 1S31 antenna was installed on the upper section of the superstructure and the 1S11 on the lower, they could turn around independently.