就通訊頻率範圍的區分來說 Extreme 是最高的...

3 – 30 MHz High frequency 高頻HF
30 – 300 MHz Very high frequency 特高頻VHF
300 – 3000 MHz Ultra high frequency 超高頻UHF
3 – 30 GHz Super high frequency 極高頻SHF
30 – 300 GHz Extremely High freq. 至高頻EHF

中文對應來源
http://www.dgt.gov.tw/chinese/Frequ...ribute-ps.shtml