Theory and Experiments of Ultra-Wideband Phased Arrays for Future Integrated Sensing and Communications

Ultra-wideband phased array antennas are the key technology for future advanced wireless systems including wireless communications, sensing, radars, navigation, microwave/millimeter-wave/THz imaging for medical and security applications, etc.The evolution of mobile communication systems in recent several decades, from 1G, 2G, 3G, 4G, 5G and 6G, shows clearly the trend towards the use of more and more frequency bands in wireless communications, and such a trend is likely to continue in future generations of wireless systems, such as the Integrated Sensing And Communications (ISAC) and the integration of Terrestrial Networks (TN) and Non-Terrestrial Networks (NTN).Both ISAC and NTN are key features of forthcoming 6G networks.In the meantime, new generations of sensing and radar imaging systems are also using more and more frequency bands.For example, earth observation using the space-borne or air-borne synthetic aperture radars (SAR) is employing multiple frequency bands such as P, L, C, X, Ku, K and Ka bands, as multi-band SAR can obtain more reliable results and higher resolution images than the traditional single-band SAR through feature-level fusion [1].To meet the demands of future generations of wireless systems, it is important to investigate the theory and practical development of ultra-wideband phased array antennas.Ultra-wideband phased array is a hot topic of research during the recent decades, and many theoretical methods and experimental developments have been reported.One typical example is an ultra-wideband phased array consisting of a large number of Vivaldi antennas.Despite that it is demonstrated to achieve ultra-wideband performance, such a phased array antenna system suffers from the problems of bulky size, large mass, complicated structures and high cost.In recent years, some ultra-wideband phased arrays using tightly-coupled dipole antennas (TCDA) or long slots have been reported [2][3][4].TCDA-based phased arrays make use of the strong coupling between radiating elements for achieving ultra-wideband performance.This is contrary to the traditional practice in phased array antenna designs in which the mutual coupling between radiating elements needs to be suppressed.This talk consists of two parts: part 1 is to give a review of the state-of-the-art development in ultra-wideband phased arrays using TCDA, and also discuss the key challenges such as common-mode resonance, loop-mode resonance, etc; part 2 is to report the theory, design and experiments of a novel ultra-wideband phased arrays using TCDA approach.The theoretical design and analysis are verified by the practical measurements of the prototype.The phased array is demonstrated to achieve state-of-the-art performance in terms of frequency bandwidth and efficiency.The results reported here are supported by the "Advanced Antenna Technology for a Smart World" Project, funded by Hong Kong Research Grant Council under the Area of Excellence (AOE) scheme.One of objectives of this AOE project is to develop compact-size ultra-wideband multi-polarization phased arrays for integrated communications, sensing and imaging in 6G and beyond.