A Broadband D-Band Cavity-Backed Coupled-Feed Patch Antenna in Wafer-Level Package Based on Heterogeneous Integrations

This article proposes a broadband cavity-backed coupled-feed patch antenna in wafer-level package (WLP) for D-band wireless communications. In the Si wafer, a metal cavity is etched right below the patch antenna to increase the thickness of the substrate under the patch. Through the heterogeneous integration technique, the cavity is filled with Rogers 5880 substrate with a thickness of
$274~\mu $
m. A 20-
$\mu $
m-thick benzocyclobutene (BCB) thin film is served as the interconnection layer on the Si wafer, enabling low-loss interconnection with RFICs through vias and transmission lines. The antenna placed on the BCB layer is excited by coupled-feed method, which can improve the design flexibility and further increase the bandwidth. The electric field distributions are used to analyze the antenna working principle, and an equivalent circuit model is developed based on it for analyzing the factors that affect impedance matching. Both the single antenna element and its array feature broadband performance with stable gain and high efficiency. The antenna array is differentially excited by a balun to avoid beam deviation and to suppress cross polarization.