Dual-Polarized Dielectric-filled Cavity Antenna with Air-Gap-Free Metasurface Loading for LTCC-based 5G-and-Beyond Antenna-in-Package Phased Arrays

Journal article, 2025

This work introduces a dual-polarized (DP) slot-excited dielectric-filled cavity antenna phased array designed for 5G and beyond AiP solutions using low-temperature co-fired ceramic (LTCC) technology. The primary challenge is to maximize a two-dimensional (2-D) beamsteering range with a compact form factor in a DP operation. Most reported LTCC AiP arrays have ≤ 55^◦ beamsteering range at 5G mmWave frequencies and lack experimental validation for DP 2-D beamsteering operation. In contrast, the proposed antenna element in the infinite array enables ±60^◦ 2-D beamsteering in the 5G n261 (27.5-28.35 GHz) band with the form factor as small as 5mm×5mm×1.3mm. This performance is achieved by introducing a wide-angle impedance matching (WAIM) structure directly at the antenna aperture, comprising a dual-layer metasurface formed by periodically arranged electrically small patches in a staggered configuration. The antenna is jointly optimized with a DP feeding network to minimize parasitics in the multilayer LTCC stack and a co-integrated printed circuit board (PCB) carrier to mitigate package-carrier coupling often neglected in previous works. It is fabricated in a single LTCC process without air gaps to ensure precise layer-to-layer alignment and eliminate losses from additional support structures inherent to conventional air-gap WAIM stacks. A custom equivalent-circuit model enables efficient analysis of scan-dependent impedance matching for the optimization. A 128-element AiP prototype employs 4×4 subarrays of four DP elements on the PCB carrier and is packaged with ball grid arrays (BGAs) to facilitate integration. This modular approach allows scaling to large arrays while considering the critical effects of the package stack-up and DP feeding. The simulated active reflection coefficient is < −8.5 dB within ±60^◦ (with a scan loss marginally above 3 dB) at 27.5-29.5 GHz. Measurements confirm simulations for all relevant performance metrics in ±60^◦ 2D-range.