Beamforming Networks

Non-Orthogonal Multibeam Network Synthesis Achieving Stein’s Limit and Implementation Based on RGW Technology

This work introduces a novel synthesis method for optimal efficiency multibeam networks. Our design method can create networks able to excite any set of non-orthogonal beams with the optimal power efficiency as dictated by Stein’s limit. To achieve this, we decompose the desired non-orthogonal excitation matrices to two orthogonal and one diagonal excitation matrices with the use of Singular Value Decomposition (SVD). Notably, the orthogonal excitation matrices are implemented as standard Nolen matrices and the diagonal matrix as a set of parallel properly designed transmission lines. To validate our design method, we design a beamforming network for a 2×2 planar antenna array. This network operates at 30 GHz and can generate four non-orthogonal beams that can scan in the azimuth and elevation planes. Our design is implemented using Ridge Gap Waveguide (RGW) technology, and its performance is characterized by simulation and measurements. Our beamformer achieves a 30% average power efficiency across its operating band, compared to the maximum theoretical efficiency of 55.5% calculated according to Stein’s limit.

D.I. Lialios, C. L. Zekios and S. V. Georgakopoulos, “Nonorthogonal Multibeam Network Synthesis Achieving Stein’s Limit and Implementation Based on RGW Technology,” in IEEE Transactions on Antennas and Propagation, vol. 72, no. 11, pp. 8184-8198, Nov. 2024, doi: 10.1109/TAP.2024.3441758.

We develop novel beamforming schemes. Specifically, we focus on hybrid beamforming solutions to address the needs of next-generation communication systems. In such hybrid architectures, analog beamforming networks play an important role.

A New Class of Full-Dimensional Planar True-Time-Delay Beamforming Networks

This work introduces a new class of low-cost, passive, planar, multibeam, true-time-delay millimeter wave (mmWave) beamforming networks that scan in both azimuth and elevation plane. Namely, the traditional Blass matrix topology, which is capable of exciting M beams in a linear array of N antenna elements, is redesigned to excite M beams in a planar array of H × V elements. Contrary to other 2D scanning multibeam networks found in the literature, the proposed design is (to our knowledge) the first planar, true-time-delay implementation. Notably, a formulation for designing M-beam (H × V ) antenna networks is derived, and an example of an 8-beam 2 × 4-antenna network is prototyped to validate the performance of the proposed approach. The measurements show good agreement with simulations, validating the proposed multibeam methodology. Specifically, our results demonstrate the capability of simultaneously generating 8 squint-free beams that can scan both the azimuth and elevation planes across the entire 24 GHz to 40 GHz range of instantaneous bandwidth.

D. I. Lialios, C. L. Zekios, S. V. Georgakopoulos and G. A. Kyriacou, “A Novel RF to Millimeter Waves Frequency Translation Scheme for Ultra-Wideband Beamformers Supporting the Sub-6 GHz Band,” in IEEE Transactions on Antennas and Propagation, vol. 70, no. 12, pp. 11718-11733, Dec. 2022, doi: 10.1109/TAP.2022.3210698.

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

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.

Current state-of-the-art RF beamformers achieve only 3:1 bandwidths.
With our novel design approach a 143% fractional bandwidth requirement (6:1), was reduced to just 11%.