For simultaneous transmit (Tx) and receive (Rx), it is a common practice, with monostatic full duplex (FD) systems, to use a single antenna and a circulator to provide isolation between the transmit and receive radio chains. However, most circulators currently on the market are designed to provide 12 to 20 dB of Tx/Rx port isolation, which is not sufficient for full duplex (FD) microwave communication. In fact, it is necessary to provide at least >30 dB of isolation to prevent the receiver desensitization that is caused by the leakage of high-power transmit signals. For this reason, practical simultaneous transmit and receive (STAR) systems require additional cancellation stages. In this paper, we present a novel STAR system that incorporates two circulators, a hybrid coupler, and a self-interference cancellation (SIC) circuit, based on a Finite Impulse Response (FIR) topology. Our design achieves an average Tx/Rx port isolation of ∼37 dB over a 25 MHz bandwidth (viz. 2.395-2.42 GHz) in simulation, with a minimum and maximum cancellations of 35 dB and 41 dB, respectively. A prototype was fabricated and tested showing good agreement with the simulations. All in all, the prototype achieved an average cancellation of 36 dB, with a cancellation range of 33 dB to 42 dB. INDEX TERMS Coupling signal, in-band full duplex (IBFD), simultaneous transmit and receive (STAR), self-interference cancellation (SIC).ELIAS A. ALWAN (Member, IEEE) was born in Aitou, Lebanon, in 1984. He received the B.E. degree (summa cum laude

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