Preferably, {HEAD ~ the microwave radiation} is at {TAIL ~ a frequency} of from twenty to 3000 MHz 
Preferably , { HEAD ~ the microwave radiation } is at { TAIL ~ a frequency } of from twenty to 3000 MHz
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH