Fig. 1: Concept of the frequency-comb-steered quasi-TTD beamformer.

a Illustration of the beamformer. The microwave signals feeding the antenna array are generated by heterodyne mixing of dual optical frequency combs. Linear frequency increments with a frequency step Δf are introduced across the antennas. Seamless and continuous beam steering can be achieved by changing Δf and the phase increment of each antenna channel. b Generalized principle of a linear antenna array. The electromagnetic waves interfere constructively at the phase front perpendicular to the beam direction. Comparison between a conventional phase-shifter-based array (c) and the proposed frequency-diverse quasi-TTD beamformer (d) for beamforming of LFM signals. The beam directions of different frequencies are dispersed for the conventional array. In contrast, all the beam directions are aligned to form a squint-free beam for the frequency-diverse quasi-TTD beamformer.