Possibilities and Challenges for a Phased Array Antenna System in ISAC: A Hardware Perspective

The upcoming generation of wireless systems is expected to integrate both communication and sensing capabilities by flexibly allocating resources, including hardware. Phased array antenna (PAA) systems are already vital in communication systems and radars and, therefore, have been intensively studied for several decades. Considering the availability of multiple review assessments for PAA implementation and signal processing, this article fills an existing gap by evaluating the hardware challenges and possibilities for sharing a PAA towards deployable integrated sensing and communication (ISAC) applications. Both types of applications impose tight and often divergent antenna-performance requirements, such as control over beam shape, scanning resolution, and side lobe tolerance. The inherent performance trade-offs, such as pencil beam for refined sensing versus broader beam for instantaneous coverage, highlight the complex design priorities that must be tailored to the application to achieve optimal joint system performance. This paper evaluates state-of-the-art antenna array structures and beamforming techniques in the context of ISAC systems. Although less popular due to their inherent limitations, passive beamforming networks are particularly highlighted for several proposed solutions, e.g., reciprocity and multibeam concept, and elaborated through a design and measurement by the authors. This article addresses the theoretical challenges that emerge while realizing a phased array out of a single element, their impact on sensing and communication performances, and finally, a summary of their mitigation techniques from the state-of-the-art. Selected simulation and measurement results from the authors support the discussions. The paper presents a set of PAA performance matrices for the ISAC system and their related joint benefits or trade-offs. The key enablers towards PAA sharing for ISAC systems, including quasi-circulator, gain-boosting lens, and electromagnetic bandgap structures, are presented, highlighting contemporary technological developments and related theoretical aspects. With the in-depth review, the authors also demonstrate proof of concept for the selected technologies through design steps, simulations, and measurements.