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).

I. Introduction

With the exponential growth in demand for high-throughput wireless communications, millimeter-wave (mmW) radio has attracted great attention. Among the mmW bands, the unlicensed 60-GHz band, which has been included in the Wi-Fi/WiGig alliance, is widely explored in the past decade. Recently, as one of the feasible solutions for highly integrated wireless systems, the 60-GHz antenna-in-package (AiP) design remains challenges in providing a wide bandwidth, high gain, and compact size simultaneously. To address these challenges, various types of AiP have been proposed and investigated, such as grid antenna [1], [2], aperture [3], [4], [5], dipole [6], [7], [8], [9], [10], [11], and patch [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23].