Article
Study of Forward and Backward Modes in Double-Sided
Dielectric-Filled Corrugated Waveguides
Pilar Castillo-Tapia
1,
* , Francisco Mesa
2
, Alexander Yakovlev
3
, Guido Valerio
4,5
and Oscar Quevedo-Teruel
1
Citation: Castillo-Tapia, P.; Mesa, F.;
Yakovlev, A.; Valerio, G.; Quevedo-
Teruel, O. Study of Forward and
Backward Modes in Double-Sided
Dielectric-Filled Corrugated
Waveguides. Sensors 2021, 21, 6293.
https://doi.org/10.3390/s21186293
Academic Editor: Yue Li
Received: 24 August 2021
Accepted: 15 September 2021
Published: 20 September 2021
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4.0/).
1
Division of Electromagnetic Engineering, KTH Royal Institute of Technology, 114 28 Stockholm, Sweden;
oscarqt@kth.se
2
Department of Applied Physics 1, E.T.S. de Ingeniería Informática, University of Seville, 41012 Seville, Spain;
mesa@us.es
3
Department of Electrical and Computer Engineering, The University of Mississippi, Oxford, MS 38677, USA;
yakovlev@olemiss.edu
4
Laboratoire de Génie Electrique et Electronique de Paris, CNRS, Sorbonne Université, 75252 Paris, France;
guido.valerio@sorbonne-universite.fr
5
Laboratoire de Gènie Electrique et Electronique de Paris, CNRS, CentraleSupèlec, Universitè Paris-Saclay,
91192 Paris, France
* Correspondence: pilarct@kth.se
Abstract:
This work studies the propagation characteristics of a rectangular waveguide with aligned/
misaligned double-sided dielectric-filled metallic corrugations. Two modes are found to propagate
in the proposed double-sided configuration below the hollow-waveguide cutoff frequency: a quasi-
resonant mode and a backward mode. This is in contrast to the single-sided configuration, which only
allows for backward propagation. Moreover, the double-sided configuration can be of interest for
waveguide miniaturization on account of the broader band of its backward mode. The width of the
stopband between the quasi-resonant and backward modes can be controlled by the misalignment
of the top and bottom corrugations, being null for the glide-symmetric case. The previous study
is complemented with numerical results showing the impact of the height of the corrugations, as
well as the filling dielectric permittivity, on the bandwidth and location of the appearing negative-
effective-permeability band. The multi-modal transmission-matrix method has also been employed
to estimate the rejection level and material losses in the structure and to determine which port modes
are associated with the quasi-resonant and backward modes. Finally, it is shown that glide symmetry
can advantageously be used to reduce the dispersion and broadens the operating band of the modes.
Keywords: corrugated waveguide; glide symmetry; higher symmetries; Bloch analysis
1. Introduction
Rectangular metallic waveguides are among the first employed microwave transmis-
sion systems [
1
]. Hollow waveguides have been broadly used, mainly because of their
low propagation losses and high-power capabilities. However, their frequency cut-off
characteristics and bulkiness limit their use in some applications. In order to overcome
these drawbacks, several studies adding metasurfaces have been conducted in order to
allow for backward modes, which can propagate below the cut-off frequency [
2
–
5
]. In [
6
–
9
],
it was demonstrated that a hollow waveguide with dielectric-filled periodic corrugations
on the bottom wall allows the propagation of backward modes. Among other possible
applications, this characteristic was advantageously employed in [
6
,
7
] to build slot-array
antennas. Corrugated waveguides have also been proposed for sensing electric and mag-
netic fields [
10
], as well as temperature in the THz regime [
11
]. Here, we propose a
waveguide with double-sided corrugations in order to increase propagation bandwidth of
the backward modes. Moreover, we show that, depending on the design of the waveguide,
it is possible to achieve an almost continuous propagation below and above the cut-off
Sensors 2021, 21, 6293. https://doi.org/10.3390/s21186293 https://www.mdpi.com/journal/sensors
