Gap-coupled Designs of Hexagonal Microstrip Antennas on Thinner Substrate Using Cavity-backed Structure

Abstract

Multi-resonator gap-coupled design of coaxially fed half-hexagonal microstrip antennas is proposed in 900 MHz frequency range. It yields an impedance bandwidth of 32 MHz (3.28%) on a thinner FR4 substrate (∼ 0.01λg). Reduction in patch area in the gap-coupled design is achieved by employing the ground plane slots. Slots reduce the fundamental mode resonance frequency on each patch, thereby realizing wideband response in a lower frequency region. With impedance bandwidth of 26 MHz (3.4%), slot cut ground plane design provides patch area reduction by 38.13% and frequency reduction by 21.8%. Enhancement in the broadside gain on a thinner lossy substrate in the gap-coupled designs is achieved by integrating a cavity-back structure which provides gain increment by nearly 2.5-3 dBi. Thus, the proposed work outlines a technique that enhances the bandwidth and reduces the patch size with an increment in the gain, on a thinner lossy substrate. An experimental verification for the obtained results is carried out that shows a close agreement.