A passive circulator with high isolation using a directional coupler for RFID

Wan Kyu Kim, Moon Que Lee, Jin Hyun Kim, Hyung Sun Lim, Jong Won Yu, Byung Jun Jang, Jun Seok Park

Research output: Contribution to journalConference articlepeer-review

57 Scopus citations


In radio-frequency identification (RFID) system, a directional coupler has been used to isolate RX from TX due to its simplicity and low cost compared with a circulator. Nevertheless, a conventional microstrip directional coupler has inherent drawback of poor isolation due to unequal phase velocity between even and odd mode. In this paper, a newly proposed circulator using a microstrip directional coupler is proposed to achieve good isolation between TX and RX. The proposed circulator is used for UHF band RFID reader with a single antenna, of which the operating frequency band is 860 MHz - 960 MHz. The measurement of the fabricated circulator using a modified directional coupler exhibits excellent isolation of 64 dB and directivity of 49 dB in its frequency band. The validity of the proposed circulator is demonstrated by comparing the TX leakage at the RX port of RFID reader system with that of a conventional directional coupler.

Original languageEnglish
Article number4015131
Pages (from-to)1177-1180
Number of pages4
JournalIEEE MTT-S International Microwave Symposium Digest
StatePublished - 2006
Event2006 IEEE MTT-S International Microwave Symposium Digest - San Francisco, CA, United States
Duration: 11 Jun 200616 Jun 2006


  • Circulator
  • Directional coupler
  • High directivity
  • High isolation
  • RFID


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