Spatiotemporal Nonreciprocal Filters: Theoretical Concepts and Literature Review

Nonreciprocal components are of paramount importance in many electronic systems. Traditionally, reliance on magnetic materials, such as ferrites, has been the basis of the functionality of such components. The internal magnetic moment under the influence of a strong external magnetic bias breaks the reciprocity of the materials
[1]
. However, today’s state-of-the-art systems demand cost-effective, miniaturized, and integrated solutions. This can be achieved with magnetless nonreciprocal devices that are capable of breaking the Lorentz reciprocity principle
[2]
. In the past decade, passive metastructures have also been devised to achieve Faraday rotation without magnetic bias. Spatiotemporal biasing of the metasurfaces initiates frequency translation and harmonic mixing properties that, in turn, generate nonreciprocity
[3]
,
[4]
. Recently, with the advent of magnetless nonreciprocal devices, time-varying circuits have been viewed as a remarkable breakthrough. This has, in fact, paved the path for researchers to develop nonreciprocal devices such as circulators
[5]
–








[14]
, isolators
[15]
–


[18]
, gyrators
[19]
, and even leaky-wave antennas
[20]
,
[21]
. Still, there remain some areas in the field of nonreciprocity that can be explored with the aid of magnetless time-varying circuits. One such area is the implementation of nonreciprocity in bandpass filters.