A Multiband FSS Director Using Aperture Interdigital Structure for Wireless Communication Systems

Abstract

This research paper proposes a multi-band frequency selective surface (FSS) director using the aperture interdigital technique. The FSS unit cell has been designed based on a basic bandpass filter (BPF) connected with an interdigital structure. With the proposed structure, the FSS unit cell size can be reduced from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /2 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /8 caused by the slow-wave effect of interdigital capacitance loaded at the end of the transmission line in the unit cell structure. Moreover, the capacitance loaded at the end of the transmission line can control the second and the third resonance frequencies to resonate as required. The unit cell has been designed at the fundamental frequency of 1.8 GHz and the controlled second and third resonance frequencies of 3.7 GHz and 5.2 GHz, respectively. The operating frequencies of the proposed FSS unit cell cover LTE band (0-1.9 GHz), Wi-MAX band (3.22GHz-4.7GHz), and WLAN band (5.15 GHz-5.95 GHz). The size of the unit cell is very compact which is 11.53 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times10.77$ </tex-math></inline-formula> mm. The designed unit cells are then connected as an array of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> , resulting in an overall size of 92.31 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times86.16$ </tex-math></inline-formula> mm. This array has been used as a director for dipole antennas designed at the frequencies of 1.8 GHz, 2.45 GHz, 3.7 GHz, and 5.2 GHz. From the simulation, the dipole antennas with the proposed FSS director have directional gains of 4.52 dB at 1.8 GHz, 3.83 dB at 3.7 GHz, and 3.29 dB at 5.2 GHz, respectively. Measurement results show the directional gains of 3.67 dB at 1.8 GHz, 3.16 at 3.7 GHz, and 3.42 dB at 5.2 GHz, respectively. The proposed FSS director has properties of multi-band operation with a compact size that can be developed for antenna covers and radomes of multi-band wireless communications.