This article presents the analysis, design, and characterization of a 61.25 GHz radio frequency identification (RFID) interrogator. Monostatic RFID systems have to solve the challenge of the transmit (TX)-to-receive (RX) leakage, which could desensitize the interrogator. Instead of suppressing or canceling this leakage, the interference of the transmitted and incident waves is exploited to demodulate the incident signal. The structure can be inserted between the power amplifier (PA) and the antenna pad of existing transmitters. It has a lower insertion loss (IL) than other ON-chip isolation structures used in monostatic interrogators reported to date. The transceiver front-end was fabricated on a 22 nm fully depleted silicon on insulator (FD-SOI) technology, and has a simple structure, where the low-power receiver requires 0.022 mm2 active area. The die was mounted on a radio frequency (RF) printed circuit board (PCB) and a general circuit board was used for baseband processing in the measurements.