. . . "At the output of the corresponding drain electrodes D11 to D14, an output signal appears having frequency components equal to ??o, 2??o, 3??o, . . . n??o where n is an integer greater than 1 and ??o is the fundamental frequency of the radio frequency input source Vrf, and where 2??o, 3??o, . . . n??o are the even and odd harmonics of the fundamental frequency ??o." . .