Miniaturised printed slot antenna with multi-ring technique for dual-band and broadband operations

Miniaturised microstrip-line-fed slot antennas with ring-shaped metallic strips for dual-band and broadband operations are investigated and verified in this study. The proposed designs implemented on a 0.8-mm FR-4 substrate show that the ring-shaped metallic strips and the feeding structure yield multiple resonant modes, achieving 66.3% size reduction. The proposed dual-band design reveals two operating bandwidths (12.4 and 46.5%) at the central frequencies of 2445 and 4813 MHz, respectively. The broadband design indicates the maximum bandwidth of 2511 MHz (69.6%) at 3606 MHz. This large operating bandwidth is obtained by choosing suitable combinations of feeding structure and multi-ring slot shapes. Simulated and experimental investigations are clearly conducted to understand their behaviours and optimise them for dual-band and broadband operations.