A Flexible Amplitude Equalizing Filter Based on Spoof Surface Plasmon Polaritons

Design of low‐pass filter with improved equalization based on lossy grounded spoof surface plasmon polaritons

“…In Figure 4B, S 11 in the equalizing band is less than −10 dB, indicating that a good momentum is achieved. The insertion loss in the low band is significantly improved compared with that in Wang et al, 10 which demonstrates that the LGSSPPs can expand the bandwidth of equalizing response effectively.…”

“…where W i and L i are the width and length of the strip, i = 1, 2, 3, ε eff is the effective permittivity, Z f is the wave impedance in space. According to Floquet theory, a fixed amplitude decay occurs accompanied by a constant phase increase when the field passes through a unit cell, therefore the voltage and current between the two boundaries of a unit cell can be represented by Wang et al, 10 as follows:…”

“…The parameters $${Z}_{1}$$, $${Z}_{2}$$, $${Z}_{3}$$, $${\theta }_{1}$$, $${\theta }_{2}$$, $${\theta }_{3}$$ can be calculated by the below equation: $$$\left\{\begin{array}{c}{Z}_{{\rm{i}}}=\frac{{Z}_{{\rm{f}}}}{\sqrt{{\varepsilon }_{\text{eff}}}(1.393+{\rm{W}}/{\rm{H}}+\frac{2}{3}ln({\rm{W}}/{\rm{H}}+1.444))}\,{\rm{W}}/{\rm{H}}\gt 1,\\ {\theta }_{{\rm{i}}}=\frac{{\text{cL}}_{{\rm{i}}}}{2\pi {\rm{f}}\sqrt{{\varepsilon }_{\text{eff}}}},\end{array}\right.$$$where W i and L i are the width and length of the strip, i = 1, 2, 3, $${\varepsilon }_{\text{eff}}$$ is the effective permittivity, $${Z}_{{\rm{f}}}$$ is the wave impedance in space. According to Floquet theory, a fixed amplitude decay occurs accompanied by a constant phase increase when the field passes through a unit cell, therefore the voltage and current between the two boundaries of a unit cell can be represented by Wang et al, 10 as follows: …”

“…The layout of the proposed SSPPs waveguide is shown in Figure 1A, which consists of numbers of the LGSSPPs unit cells with the dimensions: w 1 = 1.5 mm, w 2 = 2.9 mm, h 1 = 3.9 mm, h 2 = 3.05 mm, l = 3 mm, h = 14.9 mm. Different from the unit cell in, 10 an extended ground is set on the back of the unit cell to strengthen the confined surface wave. The surface mount resistors R t = 15 Ω are welded on the middle of the rectangular corrugated metal strips to achieve the expected equalization.…”

“…On the other hand, the spoof surface plasmon polaritons (SSPPs), as a confined slow wave structure with natural low-pass property, are suitable for the studying in wideband rejection. [7][8][9] In Wang et al, 10 a flexible amplitude equalizing filter based on SSPPs and indium tin oxide (ITO) is proposed, and the multi-function of equalization and filtering is obtained simultaneously. Although the periodic response is improved compared with the traditional equalizer, however, the ungrounded SSPPs unit cell results in poor equalization in low band, which needs further improvement.…”