Analysis and Design of Quasi-Circulating Quadrature Hybrid for Full-Duplex Wireless

Dror Regev, Erez Zolkov, Nimrod Ginzberg, Rani Keren, Shimi Shilo, Doron Ezri, Emanuel Cohen

Research output: Contribution to journalArticlepeer-review


This article presents a new electronic device - the four-port quasi-circulating quadrature hybrid (QCQH), which combines desirable features of electronic circulators and quadrature hybrids. The QCQH comprises three quarter-wavelength transmission lines and a 90° non-reciprocal phase shifter (NRPS) and is suitable for inband full duplex applications. We derive the four-port S-parameter matrix of the QCQH and the transfer functions under termination scenarios of interest. The resulting closed-form expressions are compared with the prior art electronic circulator. A 90° transmission line and lumped transformer alternatives are considered for designing a QCQH based on a two-port N-path circuit. TX isolation and transmission expressions are derived and verified against simulations, and a new wideband leakage cancellation approach is proposed. A TSMC 65 nm CMOS N-path chip is integrated on-board with a discrete, lumped, LCL transformer implementation. TX-to-antenna insertion loss of 1.4 dB and an RX NF of 4.7 dB at the frequency of 1 GHz were measured with a primary passive TX-RX isolation of 21 dB. Total isolation of more than 50 dB for an 80 MHz OFDM WiFi TX signal employing digitally equalized active leakage cancellation was achieved along with better than -40 dB TX EVM with SIC ON.

Original languageEnglish
Pages (from-to)5168-5181
Number of pages14
JournalIEEE Transactions on Circuits and Systems I: Regular Papers
Issue number12
StatePublished - 1 Dec 2021


  • Circulators
  • Full-Duplex (FD)
  • Impedance
  • Interference cancellation
  • Radio frequency
  • Scattering parameters
  • Silicon carbide
  • Transmission line matrix methods
  • electrical balanced duplexer (EBD)
  • electronic-circulator (EC)
  • impedance transparency.
  • load balancer (LB)
  • non-reciprocal phase shifter (NRPS)
  • self-interference cancellation (SIC)

All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering


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