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.

在超高频被动式频辨识系统里，读取器传送未调变过之连续波号给标，可提供能量给标也作为标反向号的载波。