Quasi-Elliptic Bandpass Frequency Selective Surface Based on Coupled Stubs-Loaded Ring Resonators

Abstract

In this paper, a novel design of frequency-selective surface (FSS) based on coupled stubsloaded ring resonators (SLRRs) is proposed. The proposed FSS exhibits quasi-elliptic bandpass filtering characteristic at C-band. And each unit cell of the structure is composed of two SLRRs coupled by a circular aperture. A novel method of transmission line (TL) model is proposed to investigate the operating principle of a single SLRR under normal incidence plane wave. Moreover, the operating mechanism of the proposed FSS is further researched with the aid of the equivalent circuit model (ECM) analysis method. Due to the symmetric and low-profile physical structure, the FSS keeps stable frequency response under oblique incident plane wave for both transverse electric (TE) and transverse magnetic (TM) polarizations. Finally, the designed FSS is fabricated and measured. And the measured results agree well with the simulated results. The measured results indicate that the proposed FSS exhibits a dual-polarized and stable bandpass frequency response with two transmission zeros (TZs) at around 5.71 and 6.87 GHz under different incident angles up to 40°.

Analytical criteria for designing multiresonance filters in scattering systems, with application to microwave metasurfaces

“…We also explain that good approximate solutions can be obtained, if an overall common phase for all σ n is allowed, according to Eqs. (23)(24)(25)(26).…”

“…By designing σ n to satisfy the appropriate condition from Eqs. (23)(24)(25)(26) according to the filter type, the pole residues in the partial-fraction expansion of H(ω) are also matched and thus the filter design is complete.…”

“…High-order (multi-resonance) filters-especially ideal standard filters (ISFs), such as Butterworth or elliptic [1]-have been designed for many types of wave physics (electromagnetic [2][3][4][5][6][7][8][9][10][11][12], mechanical [13][14][15][16][17], etc.) by a variety of techniques, including brute-force optimization of the transmission/scattering spectrum [18][19][20][21], circuit theory in the microwave regime [22][23][24][25][26][27][28][29][30][31], and coupled-mode theory (CMT) [32][33][34] for cascaded optical resonators [2][3][4][5][6][7][8]. Circuit theory and CMT provide attractive semi-analytical frameworks for filter design, but are restricted to systems composed of spatially separable components (either discrete circuit elements or weakly coupled resonances, respectively), while brute-force spectrum optimization faces several numerical challenges.…”

“…To derive these conditions, we first improve the quasi-normal-mode (QNM) expansion of the scattering matrix S [36] to ensure that S simultaneously satisfies all physical constraints of time-domain realness, energy conservation, and reciprocity, in contrast to previous QNM theory (QNMT) formulations [36,37], and we further show how low-Q resonances can be folded into a separate background scattering term C. We then use our S expansion to derive the required coupling coefficients of the resonances (QNMs) to the input and output ports in conjunction with the net background response, in order to achieve multiple configurations for the zeros of the S coefficients (generalizing previous work [38,39]) and thus realize any desired ISF. We finally apply our procedure to computationally design microwave metasurface filters that precisely match ISFs of various orders, bandwidths, and types-especially optimal elliptic filters, which were demonstrated only approximately in the past [21][22][23][24][25].…”

Synthesis of Multiband Frequency Selective Surfaces Using Machine Learning With the Decision Tree Algorithm

“…In [7], the analysis and the synthesis use the Genetic Algorithm (GA) with ECM, where the physical dimensions are obtained through the stop band, pass band and resonance frequency. More complex geometries generate new reactive elements that significantly increase the analytical complexity of the analysis, as in [8], where the ECM is used to determine the impedance matching network of transmission zeros and poles of the two-layer FSS and, as in [9], where the odd-and even-mode analysis is used to investigate the working mechanism of the FSS based on coupled stubs-loaded ring resonators.…”