A compact spiral-coupled directional coupler for a mobile RFID reader via integrated passive technology.

ABSTRACT This article presents the design and implementation of a high-performance, compact spiral-coupled directional coupler using an advanced integrated passive device (IPD) fabrication process on a GaAs substrate for use in mobile radio frequency identification (RFID) reader applications. The IPD fabrication step is introduced specifically to enable the directional coupler, which is constructed by the transformation of the intertwined mutual inductors and air-bridges, to have a compact size and high Q-factor. The fabricated coupler achieves only 0.43 dB of insertion loss S21 and it exhibits the coupling S31 of 15.7 dB and the isolation S41 of 27.2 dB. This presented coupler has an extra small size of only 0.72 × 0.82 mm2 and an operational frequency of 910 MHz, which is appropriate for use in an RFID reader system. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2142-2146, 2015 [ABSTRACT FROM AUTHOR]