Microwave Filters
S. Barzegar-Parizi
Abstract
Background and Objectives: The design of the circuit analog absorbers including resistive and conductive patterns on a dielectric substrate placed above the ground plane with a free spacer is interesting for researchers in the microwave regime. Broad absorption band can be achieved by appropriately designing ...
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Background and Objectives: The design of the circuit analog absorbers including resistive and conductive patterns on a dielectric substrate placed above the ground plane with a free spacer is interesting for researchers in the microwave regime. Broad absorption band can be achieved by appropriately designing the structure parameters that lead to matching the input impedance of the structure with the impedance of free space over a wide operating band. In this study, a wideband circuit analogue absorber including double-layer of resistive frequency selective surfaces (FSS) is proposed. Methods: The proposed structure is composed of two layers of periodic arrays of strips loaded with lumped resistors deposited on dielectric substrates and separated by an air spacer. Strips of each layer are orthogonal to each other. The structure is placed on a metallic back reflector with an air spacer. The bottom resistive FSS including resistor-loaded strips directed in the x-direction plays the effective role of producing the resonant frequencies with exciting TM polarization waves and leads to a wide high-frequency absorption band, while the top resistive FSS, including resistor-loaded strips directed in the y-direction plays the effective role in exciting the resonances for TE polarization that can produce a broad low frequency absorption band. Indeed, in each polarization, one of the resistive FSS acts as a resonator while the other resistive FSS acts as a transparent layer and transmits the wave. A circuit model for characterizing the proposed structure is presented for both TE and TM polarizations in the subwavelength regime, which shows good agreement with the full-wave simulations.Results: The results demonstrate that the reflectivity below −10 dB (absorption above 90%) obtains from 3.55 to 9.82 GHz (fractional bandwidth of 93%) under normal incidence for TE polarization while with TM incident wave excitation, the absorption above 90% from 9.44 to 20.85 GHz (fractional bandwidth of 75%) can be achieved. Conclusion: The proposed structure leads to a wideband absorber with various bandwidths corresponding to exciting TE and TM incident waves. Most of the proposed structures in the literature produce similar bandwidths for both polarizations. Therefore, a polarization-controlled wideband absorber is designed in this task.
