The Ibanez Radius (R) is a series of electric guitars produced by Hoshino Gakki, first introduced in 1987. It formed the basis for the Joe Satriani series. The first Radius model was the 540R and was originally part of the Ibanez Roadstar Pro series, together with the 540P Power and 540S Saber models also introduced in 1987. Therefore these models were known first as the PRO540R or 540R. The now common "series name + model number" model name format was introduced in 1992 for the Radius series.