“…sample, achieving 24 low reflections back to the magnetron and maximum power transfer to the sample [2]. Other authors have shown that it 25 is possible to achieve high power efficiencies by using dielectrics around the sample [3,4] or by placing the material to 26 be heated at an optimal position for which the reflection coefficient at the feeding port is minimized [5]. However, all of 27 these devices and methods used for increasing power efficiency are based on the minimization of the so-called 28 reflection coefficient at the feeding port mainly at 2.45 GHz which is the central frequency of the corresponding 2.4- assumed frequency and that, in fact, the spectrum of the magnetron varies with internal temperature, aging, 32 manufacturer model, power reflections and output power.…”