Cutoff manipulation of anisotropic reactance lining in circular waveguides

Abstract

The control of cutoffs is of great interest in designs of circular waveguides. In this paper, this topic is investigated for pure transverse-electric (TE) and transverse-magnetic (TM) modes by taking advantage of anisotropic reactance lining loadings. It is found that the cutoffs of TE and TM modes are determined by the reactance in the azimuthal and axial directions, respectively. When the reactance values are positive, the cutoff frequencies are lower than those of a normal conducting waveguide with the same cross-section. However, in contrast to the claim made in the previous literature that the negative reactance values caused the same reducing effect on the cutoffs as the positive values did, the cutoffs are found to be increased by the negative reactances. The theoretical results are validated by the simulations using commercial software, where a delicate model with an approximate curved anisotropic impedance boundary is proposed for the first time. By lowering the TE cutoffs and raising the TM ones, some intriguing applications, such as single-mode bandwidth extension and degenerate mode avoidance, are predicted, which would pave a way for designs of novel waveguide devices.

Cylindrical Waveguides for Microwave Spoof Surface Plasmon Polaritons

“…Instead, the present design works at markedly lower frequencies consistently with usual plasma production technology [37], [38]. At the same time, other solutions that operate in the microwave range target applications as stimulating the propagation of TEM waves [22], [26], [31] or reducing the cut-off frequency [30], [33]- [36]. The latter, in particular, rely on hybrid (e.g., HE 11 ) or TE waves.…”

“…Notably, the EM fields computed in Eqs. 3-5 for ρ ≤ a are equivalent to the ones obtained substituting the interface at ρ = a with a surface whose impedance reads [36]: The definition of Z s is fundamental to link the equivalent model to the actual propagation of a SSPP in a metasurfacecladded waveguide [24]. In fact, the theoretical formulation is based on the assumption (verified in the following) that the TM 01 mode described in Eqs.…”

“…Nonetheless, the main application for which cladding metasurfaces are designed is lowering the cut-off frequency of hollow waveguides with respect to conventional solutions [30]. Examples with rectangular [31], [32] and cylindrical [33]- [36] geometries are available in the literature. Notably, experimental validations of this concept proved the possibility of almost halving the cut-off frequency [31], [35].…”