Beam Squint Mitigation in Wideband Hybrid Beamformers: Full-TTD, Sparse-TTD, or Non-TTD?

TL;DR

This paper critically compares beam squint mitigation strategies in wideband hybrid beamforming, analyzing Full-TTD, Sparse-TTD, and Non-TTD architectures, with a focus on performance, cost, and practical limitations.

Contribution

It provides a comprehensive analysis of different beam squint mitigation architectures, highlighting practical limitations and offering cost-performance trade-off insights for wideband systems.

Findings

Full-TTD offers superior beam squint mitigation but at higher cost.

Sparse-TTD architectures face practical challenges due to wideband PS requirements.

Non-TTD approaches like WBBG have performance limitations in ultra-wideband scenarios.

Abstract

Beam squint poses a fundamental challenge in wideband hybrid beamforming, particularly for mmWave and THz systems that demand both ultra-wide bandwidth and high directional beams. While conventional phase shifter-based beamformers may offer partial mitigation, True Time Delay (TTD) units provide a fundamentally more effective solution by enabling frequency-independent beam steering. However, the high cost of TTD units has recently driven much interest in Sparse-TTD architectures, which combine a limited number of TTDs with a higher number of conventional PSs to balance performance and cost. This paper provides a critical examination of beam squint mitigation strategies in wideband hybrid beamformers, comparing Full-TTD, Sparse-TTD, and Non-TTD architectures. We analyze recent Non-TTD approaches, specifically the scheme leveraging the wideband beam gain (WBBG) concept, evaluating their performance and cost characteristics against TTD-based solutions. A key focus is placed on the practical limitations of Sparse-TTD architectures, particularly the often-overlooked requirement for wideband PSs operating alongside TTDs, which can significantly impact performance and implementation cost in real-world scenarios, especially for ultra-wideband applications. Finally, we conduct a cost-performance analysis to examine the trade-offs inherent in each architecture and provide guidance on selecting the most suitable hybrid beamforming structure for various fractional bandwidth regimes.