28 GHz HDI patch antenna-in-package design for 5G/6G communication systems

Abstract

This paper presents a low-cost and highly integrated stacked patch antenna-in-package (AiP) solution for millimeter-wave communication. The design features two stacked patches with unequal dimensions to enhance bandwidth via dual close resonances, together with an antiphase feeding technique that suppresses cross-polarization without extra circuit complexity. In addition, a full codesign methodology is developed, incorporating antenna feeding, stripline-based matching networks, BGA parasitic modeling, and coaxial-like transitions discontinuities. The core building block is a 2 × 2 sub-array integrated with a flip-chip beamforming IC on a standard 10-layer organic high-density interconnect (HDI) substrate. The fabricated 2 × 2 AiP module achieves a measured fractional bandwidth >15% (25.9–30.3 GHz), a realized gain of 9.3 dBi, a total efficiency exceeding 90%, and a cross-polarization level better than −40 dB at 28 GHz. To validate scalability, four identical sub-arrays are tiled to form a 4 × 4 array, which demonstrates a measured peak gain of 15.1 dBi and maintains high radiation efficiency (>78%). This work validates the proposed HDI PCB-based approach as a viable, cost-effective, and scalable solution for medium-to-large scale 5G/6G phased arrays.