Compact Multiband Adjustable and Gain-Enhanced Microstrip Antennas

Abstract

In this paper, a novel compact multiband microstrip antenna is proposed for the C and X-band applications. The antenna has the characteristics of having a simple structure with small dimensions of 20 × 20 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, printed on an FR4 substrate with a dielectric constant of 4.4 and a thickness of 1.6 mm. The antenna operates at two resonant frequencies around 6.3 GHz and 9.36 GHz, with corresponding bandwidths of 0.3384GHz and 0.3225GHz respectively defined at -10 dB reflection coefficient. The insertion of strips filled with PIN diodes leads to a shift in the first resonant frequency to 4.69 GHz or 5.87 GHz, and the second to 8.75 GHz or 9.08 GHz. The original resonances can be restored when all the diodes are turned ON. To enhance the antenna gain, a metallic plane is inserted beneath the planar antenna to reflect the radiated electromagnetic energy. This reflection enhances the antenna's radiation efficiency, resulting in a gain increase from 5.18 dB to 6.454 dB. Finally, to introduce an additional resonance frequency, a strip is placed vertically near the antenna patch. The antenna's design, analysis, and optimization were performed using the High Frequency Structure Simulator (HFSS) software, which is based on Finite Element Method (FEM) numerical method.