Design of RFID radio frequency passive circuit based on the method of Momentum

In the conventional design of microstrip directional coupler, different phase velocity between odd and even mode can lead to a lower isolation, and the leaking of carrier signal will seriously affect the performance of reader. In order to solve this problem, use mismatch effect of port impedance and balanced structure to design a kind of RF front-end passive circuit, which consist of balanced directional coupler and power divider. Besides, simulate it in the ADS through Momentum, the results show that isolation of RF front-end passive circuit could reach to -84dB, which improved the sensitivity of the receiving link and have good stability to load variation. According to the traditional power dividers, designed a improved one, Through comparing, we draw that there is a good agreement between the simulated and measured results. The design can restrain the carrier leakage to receiving link. The phase-gap among four-ports feed system respectively is about 90 degrees. The proposed four-port antenna feed system can well be used to eliminate deterioration transceiver isolation in the coupling between antenna. Therefore, the RF front-end designed in this paper can satisfy the performance requirements of UHF RFID reader.