Dual‐band circularly polarized crossed‐dipole antenna with double split‐ring resonators and a defected ground structure

A dual‐band cavity‐backed circularly polarized crossed‐dipole antenna with double split‐ring resonators (SRRs) is investigated in this paper. A pair of crossed dipoles connected by concentric ring‐delay lines is firstly designed as a circularly polarized (CP) antenna with only one CP mode. To extend the operation of the original design, a pair of the λ/4‐resonance SRRs are used to realize wider axial ratio bandwidth at higher band. At the same time, another pair of the λ/4‐resonance SRRs with larger dimension is adopted to obtain a lower frequency band, although the effect is not very satisfying. Then the cavity‐backed technology and a defected ground structure are both employed to improve the working bandwidth. The dual‐band CP antenna can be tuned into a wide bandwidth one by changing the dimensions of the larger SRRs. A good agreement between the simulated and measured results can be observed. The measured impedance bandwidths are 6.90% (3.36‐3.60 GHz) and 53.58% (4.40‐7.62 GHz). The measured 3‐dB AR bandwidth is 7.93% (3.39‐3.67 GHz) and 59.15% (4.08‐7.51 GHz).