Voltage-controlled unidirectional propagation of microwaves in metastructures ferrite/conductive elements with varactors

Microwave tunable and switchable planar non‐reciprocal three‐layer multiresonant wire–ferrite metastructure

“…non‐reciprocal microwaves propagation (non‐reciprocal isolation). Retuning of grating's resonance frequency by the use of varactors results in reversal of h ‐field rotation sense and provides propagation direction switching [5]. Really, individual elements cannot form polarisation nearly circular in every ferrite spot, besides electrical control leads to increase of ellipticity; therefore, insufficient isolation and low direct transmission ( T direct ) are observed.…”

“…Introduction: At present non-reciprocal devices with the use of metamaterials are subjects of great interest. There are magnetic-based metamaterials containing ferrite in combination with conductive inclusions [1][2][3][4][5] and magnetic-free metamaterials without the use of magnetic material, where non-reciprocity of electromagnetic waves propagation is achieved through unconventional complex methods [6][7][8]. Magnetic-based and magnetic-free metamaterials have new functionalities in comparison with conventional ferrites.…”

“…Our previous works have been devoted to microwave magnetic-based non-reciprocal planar metastructures containing ferrite plate and grating of varactor-loaded resonant conductive elements (chains or individual elements). Near resonant frequency the grating forms a surface wave with magnetic field h rotating in a plane orthogonal to the microwave field E (or static magnetic field H ) [9] and provides control by voltage [5]. Grating combines two functions: surface wave forming and electrical control.…”

“…By using array of double split rings, retuning range is 0.75 GHz (18%) with change of isolation from 9 to 25 dB, microwave propagation direction is switched to opposite at fixed frequency with change of isolation from 21 to 13 dB; T direct is changed from −5 to −9 dB in the matching absence. By using dipole elements, microwave propagation direction is switched to opposite at fixed frequency with change of isolation 13-5 dB; T direct ≈ −16 dB [5].…”

“…Measurements method: We use single-channel measurements. In this case, the non-reciprocity δT (isolation) of microwave transmission T under the FMR can be defined [5] not by reversal of the propagation direction as usually but as the difference between transmission coefficients T(H−) and T(H+). H− and H+ correspond to opposite directions of magnetisation (magnitudes of H-field are the same).…”