Slow-Wave Transmission Line Unit with Spiral-Shaped Branches and Defected Grounds for CPW

In this paper, a slow-wave transmission line unit for coplanar waveguide (CPW) is proposed, which can be used as a kind of periodic structure. For the proposed unit, the CPW transmission line is loaded with spiral-shaped branches, while the both ground planes have spiral-shaped defects. The proposed 50 Ω transmission line unit with 22.5° has more compact size than conventional case, and only occupies 28.8% size of conventional one. The operational frequency of proposed unit is 0.9 GHz, and the bandwidth can achieve 366.7%, ranged from 0 GHz to 3.24 GHz. Moreover, to verify the periodic characteristic of proposed unit, two and four unit-cells of proposed structure are cascaded respectively. Finally, the proposed transmission line unit is demonstrated to have good performance by simulated results.