Miniature Footprint of Multi-Stage Self Interference Cancellation in a STAR Radio

Simultaneous Transmit and Receive (STAR) radio architecture provides for increased data rate without excess spectrum use. A fundamental challenge in STAR radio is the suppression of high-power self-interference from the collocated antennas. For a practical STAR operation, it is required to pursue a multi-stage self-interference cancellation (SIC) strategy in a smaller footprint. To realize such a miniature high isolation STAR front-end module (FEM) operating at the Ku band, antenna coupling reduction is critical at the first cancellation stage. But this alone is not enough for practical STAR radios. Additional cancellation should be achieved through self-interference cancellation (SIC) circuits placed after the RF front end. However, for high-frequency Ku band operation (12-18GHz), isolation from passive circuitry is very difficult. In this paper, a custom-integrated five-layer high isolation RF STAR passive FEM has been proposed. The prototype is fabricated using LTCC technology to provide 70dB of isolation across 1GHz bandwidth by combining the antenna and SIC filter stage with a reduced form factor.