A New Miniaturized Low-Profile and Stable Dual-Band FSS with 2.5D Structure for ISM Bands

Abstract

Based on 2.5-Dimensional (2.5D) frequency selective surface (FSS) structures, a new miniaturized frequency selective surface structure is proposed in this work to operate as a bandreject filter in the 2.4 GHz (2400 to 2483.5 MHz) and 5 GHz (5150 to 5350 MHz and 5470 to 5725 MHz) ISM (Industrial, Scientific, and Medical) bands. The FSS has the metallization layer formed by a square loop with an internal cross loop, with each geometry being responsible for a rejection frequency range. The main characteristics of the structure are discussed, emphasizing the resonance frequency variation as a function of the increasing number of vias. Numerical results are obtained through simulations using the commercial software ANSYS HFSS. In addition, by analyzing numerical results for structures with different numbers of vias, it was possible to obtain expressions for calculating the first resonance frequency for each geometry. The cell size of the 2.5D FSS of the proposed cell is only 0.0883 λ0, where λ0 corresponds to the free-space wavelength of the lower resonance frequency. The FSS presents dual polarization, angular stability for angles up to 50° and its simulated response presented two resonant frequencies, the first at 2.65 GHz and the second at 5.34 GHz, with relative bandwidths of 38.11% and 35.96%, respectively. For comparison and validation purposes, the prototype is fabricated and measured. A very good agreement between the simulation and measurement results is observed.