Magnetless circulators based on linear time-varying circuits




Kord, Ahmed

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In a crowded electromagnetic spectrum with an ever‐increasing demand for higher data rates to enable multimedia‐rich applications and services, an efficient use of the available wireless resources becomes crucial. For this reason, full‐duplex communication, which doubles the transmission rate over a certain bandwidth compared to currently deployed half-duplex radios by operating the uplink and the downlink simultaneously on the same frequency, has been brought back into the spotlight after decades of being presumed impractical. This long‐held assumption has been particularly due to the lack of high performance low-cost and small-size circulators that could mitigate the strong self-interference at the RF frontend interface of full-duplex transceivers while, at the same time, permitting low-loss bi-directional communication using a single antenna. Traditionally, such non-reciprocal components were almost exclusively based on magnetic biasing of rare-earth ferrite materials, which results in bulky and expensive devices that are not suitable for the vast majority of commercial systems. Despite significant research efforts over the past few decades, none of the previous works managed to eliminate the magnet while satisfying all the challenging requirements dictated by the standards of real systems. In this dissertation, we introduce several newly invented magnetless circulators based on linear time-varying circuits that can overcome for the first time the limitations of all previous approaches. We analyze the presented circuits rigorously and validate them through simulations and measurements, showing unprecedented performance in all relevant metrics, thus holding the promise to enable full-duplex radios in the near future



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