the Federal Communications Commission (FCC)of the United States designated 915 ± 13 MHz and 2450 ± 50 MHz for industrial, scientific, and medical uses other than telecommunications. How-ever, the operating peak frequency of a magnetron may vary within or beyond the allocated bandwidth. the variations are caused by differences in design and manufacture of magnetrons and the generators. A magnetron may also experience frequency shifts as it ages (Cooper,2009). An important reason for the frequency shifts would be the reduction of strength of the permanent magnet in the magnetron (Decareau,1985). Finally, the operating frequency of a microwave generator also changes with the power setting during operation.