A folded reflectarray antenna with a planar SIW slot array antenna as the primary source

An integrated design of a planar source-fed folded reflectarray antenna (FRA) with low profile is proposed to achieve high gain for Q-band millimeter wave high data rate wireless communication applications. A planar substrate integrated waveguide (SIW) slot array antenna is adopted as the primary source to illuminate the proposed FRA. Considerations of the off-focus loss and the asymmetry E- and H-plane beamwidths loss of the planar source are thoroughly investigated to improve the aperture efficiency of the reflectarray antenna. A prototype is implemented and the experimental results are in good agreement with the predictions, which exhibit a measured |S₁₁| less than -10 dB over the frequency band of 41.6-44 GHz, a maximum boresight gain of 31.9 dBi at 44 GHz with the aperture efficiency of 49% and a -3 dB gain drop bandwidth of 41.8-44.9 GHz. By integrating with the planar feed, the proposed folded reflectarray antenna benefits from its low-profile, low cost, and the ability of coplanar integration with millimeter wave planar circuits while maintaining the good performance in terms of gain and efficiency.