1. A microwave heating device, comprising:a heating chamber which is designed to receive at least one product to be heated;
a microwave generating system designed to generate microwaves and including at least two radiating portions that are adapted to radiate microwaves to the heating chamber, a radiated power being associated with the radiated microwaves and, in use, a share of radiated power being reflected by the heating chamber; and
a control unit;
the microwave generating system being designed to radiate via the at least two radiating portions respective microwaves having a same frequency and different phases, wherein one of the radiating portions is a reference radiating portion and the microwaves radiated by the other radiating portion(s) has respective phase shift(s) from the microwaves radiated by the reference radiating portion, the frequency value and the phase shift value(s) defining an operational configuration of the microwave generating system, an energy efficiency being associated with each operational configuration, the energy efficiency being inversely related to a ratio of reflected power over radiated power;
the control unit being configured to operate the microwave generating system and to change the frequency and the phase shift(s) of the microwaves radiated by the microwave generating system;
the control unit being configured to obtain data of energy efficiency, as a function of operational configurations, relating to the at least one product to be heated;
the control unit being configured to run a selection procedure, in which a plurality of operational configurations are ranked according to energy efficiency and one or more operational configurations ranking high in energy efficiency are selected; and
the control unit being configured to run a heating procedure, in which the microwave generating system is operated in said one or more operational configurations selected in the selection procedure.