A thermonuclear reactor of the invention comprises an ion cyclotron resonance heating system, the ion cyclotron resonance heating system comprising: an antenna (1), the antenna having 4 signal ports, the antenna allowing a transfer of power from its 4 signal ports to an electromagnetic field produced by the antenna in a vacuum chamber (2) of the thermonuclear reactor; a multiple-input-port and multiple-output-port tuning unit (4) having 4 input ports and 4 output ports, each of the output ports being indirectly coupled to one and only one of the signal ports through a coaxial transmission line (3); 4 high-power radio-frequency amplifiers (6), the output of each of which being indirectly coupled to one and only one of the 4 input ports through a coaxial transmission line (5); and a signal generation and control unit (7).