Nonreciprocal Components Based on Switched Transmission Lines

Nonreciprocal components, such as isolators and circulators, are critical to wireless communication and radar applications. Traditionally, nonreciprocal components have been implemented using ferrite materials, which exhibit nonreciprocity under the influence of an external magnetic field. However, ferrite materials cannot be integrated into IC fabrication processes and, consequently, are bulky and expensive. In the recent past, there has been strong interest in achieving nonreciprocity in a nonmagnetic IC-compatible fashion using spatio-temporal modulation. In this paper, we present a general approach to nonreciprocity based on switched transmission lines. Switched transmission lines enable broadband, lossless, and compact nonreciprocity and a wide range of nonreciprocal functionalities, including nonreciprocal phase shifters, ultra-broadband gyrators and isolators, frequency-conversion isolators, and high-linearity/high-frequency/ultra-broadband circulators. We present a detailed theoretical analysis of the various nonidealities that impact insertion loss and provide design guidelines. The theory is validated by experimental results from discrete-component-based gyrators and isolators and a 25-GHz circulator fabricated in a 45-nm SOI CMOS technology.