Interwoven Hexagonal Frequency Selective Surface: An Application for WiFi Propagation Control

Abstract

A sub-wavelength band stop unit cell frequency selective surface, comprising six continuously interwoven hexagonal unit cells and arranged as a tessellated surface, is proposed, analyzed, simulated, and measured. The broadband and sub-wavelength characteristics of this unit cell, below the typical $\lambda _{0}/2$ , are analyzed and discussed. It has been demonstrated that by using the unit cell proposed in this paper, a 22% increase in the fractional bandwidth can be achieved along with a substantial improvement in its angular stability at high angles of incidence, compared to similar works previously published. The analysis of this unit cell is performed using the equivalent circuit model that allows relating the number of interweaves with the equivalent capacitance and inductance, thus giving a better understanding of the unit cell characterization. In addition, a frequency selective surface arranged in a 2.5D configuration is also proposed. This 2.5D configuration provides a bandwidth similar to the conventional model but with a reduction in the resonance frequency by 44%. Simulations have been validated using two prototypes, each having an overall dimension of $400\times400$ mm. To demonstrate the scalability of the design, both prototypes are designed to be used as WiFi propagation control, working as a band stop filter at 2.4 and 5.8 GHz, respectively. Transmission coefficients have been measured for TE and TM-modes using an optical bench at angles of incidence from 0 to 60°. These compare favorably with simulations performed using the frequency domain solver in CST Microwave Studio and are found to have a maximum MSE of $2.3\times 10^{-3}$ .

Keywords

• Frequency selective surfaces
• meta-surfaces
• antennas
• propagation