60-GHz Scalable LTCC Phased Array With Compact Symmetric Hybrid Feeding Network for Antenna-in-Package Application

In this article, a 60-GHz phased array with a compact symmetric hybrid feeding network in low-temperature co- fired ceramic (LTCC) technology is proposed. To improve the bandwidth and cross-polarization level, a magnetoelectric (ME) dipole with a strip and five pairs of slots is designed. Meanwhile, a theoretical model is developed to provide physical insight into the working mechanism of the ME-dipole element. To reduce the feeding loss and the element gain variation in the phased array, a symmetric hybrid microstrip (MS)/substrate-integrated waveguide (SIW) feeding network is proposed. The ME-dipole element achieves a measured $\vert {S} _{\mathbf {11}}\,\,\vert < -10$ dB and a stable gain of 4.6 ± 0.7 dBi from 55.3 to 67 GHz. By combining the ME-dipole element and the hybrid feeding network, a $4\times $ 4 antenna-in-package (AiP) phased array based on four $2\times $ 2 scalable subarrays is proposed. The total dimension is $14.75\times 14.75\times0.855$ mm. The measured results show that the fractional impedance bandwidth ( $\vert {S} _{\mathbf {11}} \vert < -10$ dB) of each element is $\ge 21.4$ % with $\le \pm $ 0.73-dBi element-to-element gain variation and ~16.9-dBi array peak gain (including ~0.35-dB simulated interconnection loss).