ABSTRACT
Conventional phased arrays operate over bandwidths that are inversely proportional to the array size. The use of true-time delays (TTDs) instead of phase shifts would eliminate the bandwidth restrictions due to beam squint. Photonic techniques for dynamically controlling the delay at the input of a phased array antenna opens an area of new powerful methods for remarkably precisely increasing the speed of beamsteering of an antenna in a desired direction. In this paper, we demonstrate a photonic-based wideband TTD beamforming network employing super-Gaussian apodized chirped fiber Bragg gratings (SGFBGs) of different lengths such as 1.5 cm, 2 cm, 2.5 cm, and many more, as well as different chirp rates, which can be used as variable TTD lines for controlling the radiation angle of the phased array antenna (the main lobe radiated by the phased array antenna can be steered squint-free between 0° and ±49.63∘), suitable for continuous beamforming at microwave frequencies in the X-band (8-12 GHz). The main purpose of using SGFBGs in a TTD module is the reduction of ripples in delay with respect to wavelength, which results in reduction in ambiguity while tuning the laser wavelength to any particular value within spectral width of FBG. To the best of the authors' knowledge, this is the first experimental demonstration that shows the impact of tuning wavelength on delay change due to SGFBGs in the RF signal fed to the respective element of the antenna array.
