A compact circularly polarized antenna using CRLH inspired transmission line and coupled ring resonator

Abstract

This paper discusses the miniaturization process and bandwidth enhancement of circularly polarized (CP) antenna using asymmetric coplanar strip (ACS) feeding. The antenna mainly uses an ACS feeding scheme on which a via-less composite right/left-handed (CRLH) transmission line (TL) inspired unit cell is implemented for antenna miniaturization and a rectangular shaped annular ring slot is introduced in the asymmetric ground plane (AGP) for generating extended CP radiation. Due to this, the intended antenna offers a compact electrical size of 0.22 λ0 × 0.35 λ0 × 0.028 λ0 at 5.5 GHz and a smaller physical dimension of 12 mm × 19.5 mm × 1.52 mm with ka = 1.32. The novelty of the antenna is to generate an improved impedance bandwidth (IBW) of (5.33–5.86 GHz) 9.90%, and enhanced axial ratio bandwidth (ARBW) of (5.33–5.79 GHz) 8.27% with less design complexity. The intended CP antenna provides a measured gain of 2.43 dBic at 5.53 GHz and radiation efficiency better than 87% is obtained by maintaining the antenna compactness without the use of complicated vias. Also, the intended antenna provides a good AR beamwidth of 80° (+40° to -40°) and positive gain values for theta = ±36° and for all phi values (phi = 00–360°) at 5.55 GHz. Moreover, the intended antenna provides 42.85% miniaturization compared to a conventional monopole antenna. Hence, the intended antenna is well suited for the 5.80 GHz WLAN (5.725–5.875 GHz), and 5.5 GHz WiMAX (5.25–5.85 GHz) applications.