Non-reciprocity with time-varying transmission lines (TVTLs)

It is well known that based on reciprocity theorem, non-reciprocity can not be realized in a lossless form if the component is made of only linear, passive, reciprocal material. Non-reciprocal microwave components such as isolators and circulators require the use of non-reciprocal material such as ferrite magnetic material. Such components are often bulky, lossy and narrow band, particularly when they are operated at the lower end of the microwave frequency spectrum. In this paper, a non-reciprocal component is envisioned with transmission lines with time-varying medium properties. The time-variance of the medium property added a new dimension to non-reciprocal component design for microwave applications and can potentially provide non-magnetic, broadband and lossless realization of isolators or circulators. One of the greatest advantages of such a design is that the device can be made compatible with the modern integrated circuit technology, which may eventually lead to monolithic integration of the complete transceiver front-end that provide isolation between transmitting and receiving path without resorting to a frequency or time diplexer.