Gain enhancement of a monopole antenna using frequency selective surface for sub-6 GHz band applications

A monopole edge-fed triple-layered double-story rectangular patch antenna was designed in this study. The antenna was loaded with a frequency selective surface (FSS) to enhance its gain and radiation efficiency. Several antennas were designed without the reflector, and in this proposed work, an FSS was placed beneath the reduced length ground plane to act as a partial reflector for the antenna's back lobes. The microstrip rectangular patch antenna with an inset feed was fabricated on a low-loss RT Duroid 5880 substrate measuring 49mm × 49mm × 1.588mm. The FSS, on the other hand, was fabricated on an FR4 substrate of the same size. The FSS consisted of an array of equally spaced 49 rectangular dipole strips. When comparing the antenna with and without the FSS, it was found that the antenna without the FSS had a gain of 2.87dBi and a -10dB fractional bandwidth (FBW) of 92.66%. However, the antenna with the introduced FSS demonstrated an improved gain of 7.76dBi (an enhancement of 4.91dBi) and a reduced -10dB FBW of 49.08%. The introduction of the FSS resulted in improved radiation characteristics, transforming the bi-directional radiation pattern into a unidirectional one, and significantly improving the front-to-back ratio (FBR). Furthermore, the radiation efficiency of the antenna without the FSS at its resonant frequency of 5.8GHz was measured to be 94.68%, while with the FSS reflecting surface, it increased to 97.88%. The antenna with the FSS achieved a reflection coefficient below -10dB over a wideband range from 3.90GHz to 6.43GHz. Consequently, the proposed antenna was deemed suitable for various applications, including 5.8GHz WLAN and 5G Sub-6GHz bands such as n46 (5150 – 5925MHz), n47 (5855 – 5925MHz), n77 (3900-4200MHz), n79 (4400-5000MHz), and n96/n102 (5925-6425MHz). Additionally, this study presented the electrical equivalent, resistive inductive capacitive (RLC) circuit of the proposed antenna.