A Low-Profile 2.4/28 GHz Dual-Band Circularly Polarized Antenna Using Structural-Reuse Technique

In this paper, a low-profile $2.4 / 28 \mathbf{G H z}$ dual-band circularly polarized (CP) antenna is proposed. The entire structure of a $2 \times 228 \mathrm{GHz}$ substrate integrated waveguide (SIW) cavity-backed CP array is reused as the $C P$ radiating patch in the 2.4 GHz band through slot coupling excitation. Open-ended stubs are used to provide gain filtering characteristics in the $\mathbf{2. 4}$ GHz band. Wide impedance bandwidths and 3 dB AR bandwidths can be achieved in both bands with high cross-band isolation, and high out-of-band suppression level has been realized in the 2.4 GHz band. All these merits make this proposed antenna a promising candidate for some applications in B5G/6G era.