In a UHF passive RFID system, a reader transmits an unmodulated continuous wave (CW) to tags, which not only provides energy to tags but also serves as the carrier of tag backscatter signals.

在超高频被动式射频辨识系统里，读取器传送未调变过之连续波讯号给标，不但可提供能量给标也作为标反向散射讯号的载波。