An electromagnetic cooking device comprising: an enclosed cavity; a set of radio frequency feeds (26A-26D) configured to introduce electromagnetic radiation into the enclosed cavity to heat up and prepare food; a set of high-power radio frequency amplifiers (18A-18D) coupled to the set of radio frequency feeds (26A-26D), each high-power amplifier (18A-18D) comprising at least one amplifying stage configured to output a signal that is amplified in power with respect to an input radio frequency signal; a signal generator coupled to the set of high-power radio frequency amplifiers (18A-18D) for generating the input radio frequency signal; and a controller configured to: cause the signal generator and selected ones of the set of high-power amplifiers (18A-18D) to output a radio frequency signal of a selected frequency, a selected phase value and a selected power level, wherein the selected frequency is selected from a set of frequencies in a bandwidth of radio frequency electromagnetic waves, the selected phase value is selected from a set of phase values of radio frequency electromagnetic waves, and the selected power level is selected from a set of power levels; and identify the resonant modes excited within the enclosed cavity, characterised in that the selected phase value is selected from a set of phasors with an in-phase relationship to activate resonant modes of even symmetry within the enclosed cavity and from a set of phasors with an antiphase relationship to activate resonant modes of odd symmetry within the enclosed cavity. an enclosed cavity; a set of radio frequency feeds (26A-26D) configured to introduce electromagnetic radiation into the enclosed cavity to heat up and prepare food; a set of high-power radio frequency amplifiers (18A-18D) coupled to the set of radio frequency feeds (26A-26D), each high-power amplifier (18A-18D) comprising at least one amplifying stage configured to output a signal that is amplified in power with respect to an input radio frequency signal; a signal generator coupled to the set of high-power radio frequency amplifiers (18A-18D) for generating the input radio frequency signal; and a controller configured to: cause the signal generator and selected ones of the set of high-power amplifiers (18A-18D) to output a radio frequency signal of a selected frequency, a selected phase value and a selected power level, wherein the selected frequency is selected from a set of frequencies in a bandwidth of radio frequency electromagnetic waves, the selected phase value is selected from a set of phase values of radio frequency electromagnetic waves, and the selected power level is selected from a set of power levels; and identify the resonant modes excited within the enclosed cavity, characterised in that the selected phase value is selected from a set of phasors with an in-phase relationship to activate resonant modes of even symmetry within the enclosed cavity and from a set of phasors with an antiphase relationship to activate resonant modes of odd symmetry within the enclosed cavity. cause the signal generator and selected ones of the set of high-power amplifiers (18A-18D) to output a radio frequency signal of a selected frequency, a selected phase value and a selected power level, wherein the selected frequency is selected from a set of frequencies in a bandwidth of radio frequency electromagnetic waves, the selected phase value is selected from a set of phase values of radio frequency electromagnetic waves, and the selected power level is selected from a set of power levels; and identify the resonant modes excited within the enclosed cavity, characterised in that the selected phase value is selected from a set of phasors with an in-phase relationship to activate resonant modes of even symmetry within the enclosed cavity and from a set of phasors with an antiphase relationship to activate resonant modes of odd symmetry within the enclosed cavity.