Gain enhancement of a wideband rectangular ring monopole millimeter-wave antenna using artificial magnetic conductor structure

In this article, the design and development of an artificial magnetic conductor (AMC)-backed compact wideband rectangular ring monopole antenna with high gain is proposed for millimeter-wave (mmWave) applications. It is constructed through stacking a coplanar waveguide (CPW)-fed rectangular ring patch monopole antenna over a square modified AMC reflector surface of 5 × 5 periodic unit cells. Primarily, the ring monopole antenna of size 1.21λ₀ × 1.21λ₀ × 0.023λ₀ (at 28 GHz) is designed and exhibits wide impedance bandwidth of 30.64% (25.98–35.38 GHz, 9.4 GHz), a peak gain of 4.86 dBi and front-to-back ratio (FBR) up to 5.2 dB. To enhance the radiation performance of the monopole antenna, a periodic lattice of 5 × 5 unit cells modified square AMC surface with a gap of 0.84λ₀ is proposed and it functioned as reflector which enhances the peak gain of about ~77% and it contributes FBR up to 15 dB. Measured results of the modified square AMC-backed monopole antenna reveal a wide impedance bandwidth of 31.27% (25.90–35.50 GHz, 9.6 GHz), a peak gain of 8.59 dBi, and stable radiation characteristics.