The in-band full-duplex (IBFD) wireless system is a promising candidate for 6G and beyond, as it can double data throughput and enormously lower transmission latency by supporting simultaneous in-band transmission and reception of signals. Enabling IBFD systems requires a substantial mitigation of a transmitter (Tx)’s strong self-interference (SI) signal into the receiver (Rx) channel. However, current state-of-the-art approaches to tackle this challenge are inefficient in terms of performance, cost, and complexity, hindering the commercialization of IBFD techniques. In this work, we devise and demonstrate an innovative approach to realize IBFD systems that exhibit superior performance with a low-cost and less-complex architecture in an all-passive module. Our scheme is based on meticulously combining polarization-division multiplexing (PDM) with ferromagnetic nonreciprocity to achieve ultra-high isolation between Tx and Rx channels. Such an unprecedented conception has become feasible thanks to a concurrent dual-mode circulator—a new component introduced for the first time—as a key feature of our module, and a dual-mode waveguide that transforms two orthogonally polarized waves into two orthogonal waveguide modes. In addition, we propose a unique passive tunable secondary SI cancellation (SIC) mechanism, which is embedded within the proposed module and boosts the isolation over a relatively broad bandwidth. We report, solely in the analog domain, experimental isolation levels of 50, 70, and 80 dB over 340, 101, and 33 MHz bandwidth at the center frequency of interest, respectively, with excellent tuning capability. Furthermore, the module is tested in two real IBFD scenarios to assess its performance in connection with Tx-to-Rx leakage and modulation error in the presence of a Tx’s strong interference signal.

中文翻译：

---

结合偏振分复用和铁磁不可逆性，实现全双工无线系统的带内超高隔离度

带内全双工 (IBFD) 无线系统是 6G 及更高版本的有希望的候选者，因为它可以通过支持同时带内传输和接收信号，使数据吞吐量加倍并大大降低传输延迟。启用 IBFD 系统需要大幅减轻发射机 (Tx) 进入接收机 (Rx) 通道的强自干扰 (SI) 信号。然而，当前应对这一挑战的最先进方法在性能、成本和复杂性方面效率低下，阻碍了 IBFD 技术的商业化。在这项工作中，我们设计并演示了一种创新方法来实现 IBFD 系统，该系统在全无源模块中以低成本和不太复杂的架构展现出卓越的性能。我们的方案基于将偏分复用 (PDM) 与铁磁不可逆性精心结合，以实现 Tx 和 Rx 通道之间的超高隔离。由于并发双模循环器（首次引入的新组件）作为我们模块的关键特征，以及将两个正交偏振波转换为两个正交波导模式的双模波导，这种前所未有的构想变得可行。此外，我们提出了一种独特的无源可调辅助 SI 消除 (SIC) 机制，该机制嵌入到所提出的模块中，并在相对较宽的带宽上增强隔离度。我们报告，仅在模拟域中，在感兴趣的中心频率下，在 340、101 和 33 MHz 带宽上分别达到 50、70 和 80 dB 的实验隔离水平，并具有出色的调谐能力。此外，该模块还在两个真实的 IBFD 场景中进行了测试，以评估其在存在 Tx 强干扰信号的情况下与 Tx-to-Rx 泄漏和调制错误相关的性能。