Comment on “Hybrid Spoof Surface Plasmon Polariton and Substrate Integrated Waveguide Broadband Bandpass Filter With Wide Out-of-Band Rejection”

The dispersion diagrams for the proposed spoof surface plasmon polariton (SSPP) unit
[1, Fig. 1(b)]
and the substrate-integrated waveguide (SIW) unit
[1, Fig. 1(c)]
are plotted in
[1, Fig. 2]
, which are incorrect and the correct dispersion curves for the same are presented here, as shown in
Fig. 1
. The dispersion curves are analyzed and plotted for mode-1 simulation in the eigenmode solver of CST microwave studio. Furthermore, the dispersion curve with optimized dimensions,
$L_{i}$
and
$W_{i}$
, where
$i\in (5,\ldots ,8)$
for the SSPP part
[1, Fig. 1(a)]
, is shown in
Fig. 2
. The lower and upper cutoff frequencies for the passband of the filter are defined from the structural parameters of SIW and SSPP units, respectively. It can be seen from the dispersion curves of SIW and SSPP units
[1, Fig. 2]
that the lower cutoff frequency obtained from the SIW unit is around 7 GHz, while the upper cutoff frequency obtained from the SSPP unit is around 6 GHz (
$W=15$
mm of the SIW unit and
$W=8$
mm of the SSPP unit). However, only the cutoff frequency in the dispersion curve of the SIW unit is correct, from where the lower cutoff frequency of the proposed BPF is set around 7 GHz. The dispersion curve of the SIW unit
[1, Fig. 1(c)]
with correct distribution trend is shown here in
Fig. 1(b)
. The passband of the proposed hybrid SSPP-SIW filter is about 7–11 GHz, and hence, the correct upper cutoff frequency for passband of the filter, as it can be seen from our corrected dispersion curve of the SSPP unit [see
Fig. 1(a)
], is about 11 GHz. It can also be noted that
$p$
is the period of SSPP in our corrected dispersion curves.