Abstract: An ultra-high frequency RF identification reader module is designed in this paper, which supports the international standard ISO/ IEC 18000-6C and the Chinese standard GB/ T 29768-2013. High isolation is achieved by a directional coupler based double-tuning RF transmit-receive circuit with a compact structure, which alleviates the linearity requirements of the receiver front-end. By utilizing the coupled signal from the directional coupler as the local-oscillation signal of the demodulator, the correlation between the local-oscillation signal and the RF self-jammer is improved, and the residual phase noise of the down-converted baseband signal is reduced. The designed reader module operates in 920-925 MHz band with a saturate output power of 29.6 dBm, and the inventory range is larger than 15 m for both the 6C tag and the Chinese standard tag. The miniaturization of the reader module is realized by using the compact transmit-receive isolation circuit and 3D stacked package printed circuit boards, and the volume is only 70 mm*60 mm*15 mm.