This work presents a dual-band (3.5/26 GHz) shared-aperture antenna with high aperture reuse ratio and high isolation. The proposed 26-GHz 4 Â 4 substrate integrated waveguide (SIW) cavity-backed slot array antenna consists of four hybrid TE 130 -TE 310 -mode SIW cavities, which can simplify the design of feeding network. The radiating slots are unequally offset and inductance windows are added for good impedance matching. The entire structure of the 4 Â 4 slot array antenna also functions as an equivalent TM 10 -mode patch antenna at 3.5 GHz. The resonant frequency of the patch is fine-tuned by inserting an air gap instead of enlarging the patch length, thus ensuring high aperture reuse ratio. To enhance channel isolation, the patch is designed with a bandpass filtering response centered at 3.5 GHz by introducing a stub-loaded resonator feeding structure. For demonstration, a prototype of the proposed dual-band antenna was fabricated and measured. The measured results show that the proposed antenna achieves excellent dual-band performance, and its aperture reuse ratio and channel isolation are as high as 87.5% and 62 dB, respectively. K E Y W O R D Saperture reuse ratio, cavity-backed antenna, dual-band antenna, shared-aperture antenna

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