6G Beamforming Antenna-in-Package

Abstract

As the world is getting used to 5G technology, 6G is already on the horizon. With the ultimate goal of very low latency communication and Tbps data rates, 6G supports new wireless technologies such as virtual and augmented reality and autonomous driving. In this new generation of wireless communication, high frequencies up to 100 GHz are used which causes antenna arrays to shrink to the size of a post stamp. Antenna-in-Package (AiP) is an emerging technology that integrates these antennas directly in the packaging material of IC’s. This brings the benefit of high level of integration, making beamforming IC’s an all in one system for communications. Despite this, high integration also comes with challenges. These small antenna systems generate heat on a small footprint which emphasizes the need for a low-loss, efficient system. Moreover, free-space path loss is proportional to frequency so high radiated power is needed, further emphasizing the need for improved efficiency. Lastly, space inside the IC and package material is limited which requires compact solutions for the system’s components. Literature has shown that PA-antenna co-design can reduce losses at the PA-antenna interface by matching the antenna impedance to the impedance of the power amplifier, omitting the need for lossy impedance matching networks. This method, called direct impedance matching, has shown to improve power added efficiency (PAE) in antenna systems with single radiating elements and fixed linear arrays. Nevertheless, the advantage of direct impedance matching has not yet been demonstrated for phased array antennas with active beam forming/steering.

This work demonstrates a novel analysis of PA-antenna co-design at 96 GHz using a 8x8 cavity-backed dual-polarized pin-fed stacked patch array. Two versions of this antenna array are designed in Ansys HFSS, one with an antenna impedance of 50 Ω, the benchmark, and one with a lower impedance of 25 Ω. Both designs are made on a custom package laminate stack-up and are compatible with pin-fed AiP technology. Using Keysight ADS, the antenna designs are co-simulated with an RF front-end circuit comprised of a single tone AC signal, ideal 1-64 channel power divider, ideal continuous phase shifters and realistic SiGe Class A cascode power amplifiers. In this setup, the 50 Ω reference antenna is connected to the PA’s with a matching network in between. Because the 25 Ω antenna array matches the optimal output impedance of the PA, it is directly connected. The performance of both antenna arrays are compared, with the focus on PAE and radiation characteristics. The results show that by going for a directly matched antenna the PAE of the system increases by 15.6% for a broadside beam and 30.4% with a scanned beam (θ = 45◦, φ = 45◦). EIRP for broadside and scanned beams increased from 50.3 W to 56.3 W and from 31.1 W to 37.9 W respectively. Bandwidth, gain, radiation efficiency and side-lobe levels were similar in both arrays but the 25 Ω antenna had 4 dB higher levels of cross-polarized radiation and a 4 dB stronger back-lobe behind the antenna. The advantage of higher efficiency and radiated power outweighs these drawbacks and makes direct impedance matching a good design strategy for 6G beamforming AiP technology.