A Metamaterial Loaded High Gain Low Profile RHCP Microstrip Antenna for X-Band Applications

Abstract

This paper presents the design of a right-hand circularly polarized (RHCP) microstrip antenna loaded with metamaterial to achieve high-gain performance. The metamaterial (MTM), a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5 \times 5~$ </tex-math></inline-formula> array of unit cells with a negative refractive index, is designed on one-sided FR4 dielectric material with dimensions <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.79\lambda _{0} \times 0.79\lambda _{0} \times 0.023\lambda _{0}$ </tex-math></inline-formula>, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free-space wavelength at 8.76 GHz. Both the antenna and the unit cells are designed on an FR4 substrate with a loss tangent of 0.02 and relative permittivity of 4.4. The antenna and MTM maintain the same area, with an air gap of 1 mm between them. The overall structure achieves a gain of 8.1 dBic at 9.5 GHz with stacking, compared to 4.4 dBic without the MTM stacking. The measured bandwidth of the proposed antenna is 1.98 GHz (8.76-10.74 GHz), which falls within the lower X-band, making it suitable for both military and maritime radar applications.