How Stability of Hybrid Coupler Characteristic Affects Front-End Isolation of In-Band Full Duplex System

Soheyl Soodmand, Kevin A Morris, Mark A Beach

Research output: Chapter in Book/Report/Conference proceedingConference Contribution (Conference Proceeding)

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In In-Band Full Duplex (IBFD) transceivers, Electrical Balance Duplexers (EBDs) provide Transmit (TX)-Receive (RX) isolation to implement a form of self-interference (SI) cancellation to facilitates simultaneous transmission and reception from a single antenna. EBD works by coupling transmitter, receiver, antenna, and balancing impedance using a hybrid coupler. The balancing impedance in the EBD needs to be equal as much as possible to the antenna impedance to achieve a high isolation while the antenna impedance variations limit the isolation bandwidth. Hybrid couplers are also not ideal elements, and their S parameters are variable in frequency domain. An antenna with a stable impedance, designed by authors, has been connected in this work to two different hybrid couplers in the EBD stages. One coupler is a commercial coupler and the other one, designed by the authors, has more S parameter stability in the frequency domain than the commercial one. It is shown that by using the designed coupler in the front-end EBD stage more stable isolation bandwidth and 45% better isolation value at ultra-wideband range of 1.5- 3.5GHz are obtained, in comparison when using the commercial one.
Original languageEnglish
Title of host publication2021 IEEE International IOT, Electronics and Mechatronics Conference (IEMTRONICS)
PublisherInstitute of Electrical and Electronics Engineers (IEEE)
Number of pages6
ISBN (Electronic)978-1-6654-4067-7
ISBN (Print)978-1-6654-1160-8
Publication statusPublished - 14 May 2021
EventInternational IOT, Electronics and Mechatronics Conference: IEMTRONICS 2021 - Toronto, Canada
Duration: 21 Apr 202124 Apr 2021


ConferenceInternational IOT, Electronics and Mechatronics Conference
Abbreviated titleIEMTRONICS 2021


  • Interference cancellation
  • Frequency-domain analysis
  • Transmitting antennas
  • Receiving antennas
  • Couplers
  • Bandwidth
  • Stability analysis


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