A Cost-Effective Wideband Dual-Polarized L-Shaped Probe-Fed Phased Array Antenna for 60-GHz AiP Applications

Abstract

This article presents a wideband dual-polarized L-shaped probe-fed stacked patch antenna element and a 16-element phased array antenna prototype for 60-GHz antenna-in-package (AiP) applications. The primary objective is to overcome the fabrication restrictions and achieve high-performance, cost-effective AiP module using an organic multilayer industry-standard high-density interconnect (HDI) process (100-/230- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> minimum via/land size). A new L-shaped probe-fed structure, which functions as a monopole antenna, is implemented to enhance the bandwidth and gain performance of the stacked patch antenna. With help of the comprehensive mode analysis method, the polarization coupling mechanism is highlighted, and an isolated patch is introduced, improving the antenna polarization isolation by up to 7 dB. To connect RFIC, considering limited fabrication accuracy and the AiP structure features, a broadband vertical transition structure is designed using the half-wavelength impedance transformation technique, and its working mechanism is analyzed theoretically through a distributed equivalent circuit model. Furthermore, the impact of variations in key dielectric properties on important AiP characteristics is analyzed, and the process control guidelines are provided. Thermal simulations using a heatsink solution are performed to address thermal issues. For demonstration, an antenna element and a 16-element antenna array prototype are designed, fabricated, and measured. For both polarizations, measurements indicate that the proposed antenna element has a fractional impedance bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert &lt; -10$ </tex-math></inline-formula> dB) of 23.1%, and its polarization isolation is better than 20 dB. Moreover, their peak gain is above 5.45 dBi. For the 16-element antenna array, each element achieves a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11} \vert $ </tex-math></inline-formula> below −10 dB from 51 to 64 GHz with 4 ± 1 dBi gains.