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Bandpass Absorptive Frequency-Selective Structure Using Double-Sided Parallel-Strip Lines

A novel design method of bandpass absorptive frequency-selective structure (AFSS) is presented in this letter. The proposed AFSS is based on double-sided parallel-strip lines (DSPSLs), which is different from those based on the conventional parallel L-C resonator. Its lossy layer of a unit cell consists of the DSPSLs and striplines loaded with four lumped resistors, in which one end of the DSPSL connects to the stripline and the other end is open. The proposed AFSS is implemented by mounting the lossy layer in front of a bandpass FSS, which is constructed by a square-loop slot etched on a metal plate. In the transmission band, the lossy layer is designed as an infinite impedance by introducing the DSPSLs, and then, the lossy layer is transparent to the incident wave. In the absorption bands, the incident wave is reflected by the bandpass FSS and then dissipated by the lossy layer. The proposed AFSS is fabricated and measured. It has a passband of 5.49–6.09  GHz, two absorption bands of 2.63–5.19 GHz and 6.37–8.45 GHz, and stable performance under oblique incidence. It has a compact structure of 0.18λa × 0.18λa × 0.09λa, where λa is the wavelength of the lowest absorption frequency.