Efficient Photonic Beamforming System Incorporating a Unique Featured Tunable Chirped Fiber Bragg Grating for Application Extended to the Ku-Band

• Published in: IEEE transactions on microwave theory and techniques Vol. 68; no. 5; pp. 1851 - 1857
• Main Authors: Srivastava, Nimish Kumar, Parihar, Reena, Raghuwanshi, Sanjeev Kumar
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antenna arrays; Antennas; Apodization; Beamforming; Bragg gratings; Broadband; Chirp; Continuous beams; Delays; Electromagnetic wave; erbium-doped fiber amplifier (EDFA); Far fields; Fiber gratings; Gratings; linearly chirped fiber Bragg grating (LCFBG); Mach–Zehnder modulator (MZM); Microwave frequencies; Optical refraction; Parameters; phased-array antenna (PAA); photo-detector (PD); Photonics; raised cosine apodized LCFBG (RCFBG); Reflectance; Superhigh frequencies; Time lag; Trigonometric functions; true-time delay (TTD); Voltage standing wave ratios
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2019.2961889

This article demonstrates a photonic-based wideband true-time delay (TTD) beamforming network employing a raised cosine apodized linearly chirped fiber Bragg grating (FBG) of varying lengths, such as <inline-formula> <tex-math notation="LaTeX">50\,\,{\times \,\,10^{-3}} </tex-math></inline-formula> m, <inline-formula> <tex-math notation="LaTeX">45\,\,{\times \,\,10^{-3}} </tex-math></inline-formula> m, <inline-formula> <tex-math notation="LaTeX">40\,\,{\times \,\,10^{-3}} </tex-math></inline-formula> m, and <inline-formula> <tex-math notation="LaTeX">35\,\,{\times \,\, 10^{-3}} </tex-math></inline-formula> m, and different chirp parameters <inline-formula> <tex-math notation="LaTeX">25\,\,{\times \,\, 10^{-9}} </tex-math></inline-formula> m, <inline-formula> <tex-math notation="LaTeX">35\,\,{\times \,\, 10^{-9}} </tex-math></inline-formula> m, <inline-formula> <tex-math notation="LaTeX">6\,\,{\times \,\, 10^{-8}} </tex-math></inline-formula> m, and <inline-formula> <tex-math notation="LaTeX">8{\,\,\times \,\,10^{-8}} </tex-math></inline-formula> m. The proposed scheme can be used as variable TTD lines having a much lower ripple factor compared with the previously studied apodized linearly CFBG for controlling the radiation angle of phased-array antenna (PAA), i.e., the main lobe radiated by the PAA can be steered squint-free from 0° to ±36.8° suitable for continuous beam forming at microwave frequencies 8-12 GHz extended up to Ku-band. To the best of our knowledge, this is the first experimental demonstration that shows the impact of tuning wavelength on delay change due to raised cosine apodized CFBG in the RF signal fed to the respective element of the antenna array. Four sets of <inline-formula> <tex-math notation="LaTeX">1\times4 </tex-math></inline-formula> PAAs have been fabricated with the required electrical parameters, such as reflection coefficient (<inline-formula> <tex-math notation="LaTeX">S_{11} </tex-math></inline-formula>), voltage standing wave ratio, gain, far-field radiation pattern, and so on, to show the photonic feed idea. In addition, FBG's having raised cosine apodization function is fabricated in our collaborative laboratory.