Enhancing Aperture Efficiency for Single-Feed Dual-Band Microstrip Array With a High Frequency Ratio

Dual-band microstrip antenna (MSA) arrays are widely used in applications requiring high gains. However, obtaining aperture efficiencies in both bands simultaneously for a single-feed, dual-band MSA array with a high frequency ratio (FR) is challenging. Traditional methods require separate elements to serve as different radiators, and the lower frequency (LF) elements typically occupy a large area but do not contribute to higher frequency radiation, causing a low aperture efficiency. Here, we propose a novel high aperture efficiency dual-band MSA array design, which is based on parasitic elements loaded microstrip split-ring antennas (MSRAs). The MSRA operates in 1st and 3rd order modes to achieve a high frequency ratio, and it offers decent gains, a low mutual coupling, and a compact size. In addition, the MSRA works as a radiator at LF, while serving as both radiator and exciter simultaneously for parasitic elements at HF. The final array is designed, fabricated, and measured, at 0.9 GHz and 2.4 GHz in the Industrial, Scientific, and Medical bands. The measurement result has validated the proposed method, and shows that the final array design has the highest total aperture efficiency among all the single-feed high-gain MSA arrays with a high FR, to the best knowledge of the authors (90.4% at 0.92 GHz and 73.2% at 2.43 GHz).