Radiation Pattern Optimization for QFN Packages With On-Chip Antennas at 160 GHz

On-chip antennas are frequently used as radiating elements for monolithic microwave integrated circuits (MMICs) operating above 100 GHz. Their radiation pattern is wide since the radiator extension is typically about half wavelength. In a package, the wide radiation pattern is easily disturbed by interference from parasitic radiation of the package. In this paper, an approach to minimize and adjust the interference of the package is proposed and applied to a quad flat no leads (QFN) package housing. A structured metal sheet positioned between chip and exposed pad is used to generate enough degrees of freedom for the optimization of the 3-D-radiation pattern in open-cavity and molded QFN packages. For the open-cavity QFN package, a U-shaped slot is introduced, which reduces the propagation of surface waves to the sides and creates a uniform radiation pattern. For the molded QFN package with opening around the on-chip antenna, a corrugated metal sheet is introduced. This leads to a robust packaged radar MMIC with an on-chip antenna at 160 GHz, which provides a directed radiation pattern to boresight. Both optimized radiation patterns are well suited for the illumination of dielectric lenses, which results in a higher lens gain and a lower sidelobe level of the lens pattern compared to the standard QFN packaging. The proposed concepts are verified by measurements for the open-cavity and molded QFN packages at 160 GHz.