A Novel RF to Millimeter Waves Frequency Translation Scheme for Ultra-Wideband Beamformers Supporting the Sub-6 GHz Band

Abstract

This work introduces a new class of ultra-wideband beamforming networks (BFNs) that covers the legacy sub-6 GHz bands for both traditional and fifth-generation (5G) satellite and terrestrial communication systems. To cover the multioctave sub-6 GHz bandwidth, we translate the microwave-photonics concept to the radio frequency (RF)-millimeter waves (mm-waves) regime. Based on our novel approach, the desired RF frequency, a sub-6 GHz signal, is first up-converted to a mm-wave frequency, where it undergoes the desired processing (i.e., the required time delays are introduced), and then it is down-converted back to the initial RF frequency for transmission through the antenna array. An example beamforming system is developed to validate the performance of our proposed approach. Also, a modified true-time-delay (TTD) Blass matrix is designed for this system to perform the analog beamforming. This Blass matrix is prototyped, and its performance is validated using simulations and measurements. Our results show that our proposed BFN supports a 6:1 bandwidth, which is the highest bandwidth ever reported in the literature. Additionally, our proposed approach can be extended to significantly higher bandwidths if high mm-wave frequencies are used in our up-conversion stage.