Collaborative Research: CIF: Medium: Ultrawideband Communications and Sensing with True Time Delay Arrays in the Upper Midband

Wireless communications, which has become an essential tool both for American consumers and the US industry, requires constantly increasing data rates to accommodate growing consumer demands. The US frequency regulator (Federal Communications Commission FCC) is currently making available new spectrum in the frequency range 7-24 GHz, also known as ‘’upper mid-band”, to satisfy this demand. In order to efficiently use this spectrum, it is necessary to deploy adaptive antenna arrays at both base stations and user locations; such adaptive arrays can direct the transmissions into specific directions, thus reducing interference to other users, and extending the range over which wireless links can be sustained. The use of antenna arrays can reduce transmitted power as well. While adaptive antenna arrays have been widely used in the past, modifying them to communicate over the very wide bandwidth available in the upper mid-band presents a huge challenge. Conventional phased-array technology needlessly divides the upper mid-band into three or four sub-bands, each served by a dedicated narrowband antenna array. This project aims to develop a single wideband antenna array to communicate over the entire upper mid-band, in turn requiring a complete rethinking of both antenna structures and antenna adaptation algorithms, in addition to the development of new mathematical tools. A new generation of large ultra-wide-band (UWB) antenna arrays would offer powerful sensing capabilities on top of their communication functions. This research could materially improve the global competitiveness of the United States in wireless technologies. The standard phase-shift techniques that underpin antenna beamforming for narrowband operating conditions is not effective for ultra-wide-bandwidth (UWB) operation. To overcome this limitation, this project will develop “true time delay” (TTD) beamforming methods necessary for deployment of UWB adaptive antenna arrays. The project exploits the fact that TTD beamforming is mathematically equivalent to the Radon transform, which has been extensively applied to computer tomography as well as to wide-band geophysical signal processing. The traditional space/frequency characterization of narrowband beamforming is not valid in the extremely large bandwidth regime of UWB communications. In contrast, the Radon transform accurately describes the mathematics of beamforming in the UWB space/time domain. Aperiodic arrays, which have been explored for both communication and sensing, have received little attention in the context of UWB operation, but are expected to have significant benefits for this operating regime; their optimization will also be analyzed via the Radon transform. To address the problem of UWB impedance matching, the project investigates the radical idea of not doing impedance matching of the antenna to the channel: rather it is proposed to drive the antenna with high impedance current sources during the tramsmit stage and to measure open circuit voltages during the receive stage. The research combines the development of communications theory with the development of experimental prototypes to demonstrate this novel approach to UWB space-time communication systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.