Design and investigation of configurable photonics true time delay line-based beamsteering network

Recently there is increasing interest in microwave photonics (MWP) to process wideband microwave signals using photonic technology. Beam-steering and -forming networks for phase array antennas (PAAs) have been successfully and efficiently implemented using MWP incorporating a photonic true time delay line (TTDL). The delay line is designed according to the operating microwave frequency fmw and number of radiating elements N of the PAA and cannot be adopted efficiently for other PAAs operating at different parameters values. Future wireless communication base stations will deal with PAAs having different values of fmw and N. Therefore, it is essential to design a configurable MWP-based beamsteering and -forming networks. In this paper, a configurable photonic TTDL is proposed for beamsteering network. The delay line consists of cascaded linearly chirped fiber Bragg gratings (LCFBGs) whose number is adopted according to the operating frequency, number of radiating elements, and steering angle. The simulation results reveal that a fiber Bragg grating (FBG) designed with 80 mm length and modified Gaussian apodization offers a 562.12 ps time delay difference across its reflectively spectrum bandwidth (4.07 nm). The steering network uses 3, 2, and 1 LCFBGs for 8-PAAs operating with 2.4, 5.8, and 10 GHz, respectively. Then three patch radiating elements operating at 2.4, and 5.8 GHz are designed and experimentally fabricated. The radiation pattern performance of these radiating elements are simulated and the results are found to be closed to experimental data. Accordingly, three PAAs incorporating these radiating elements are designed and their scanning capabilities based on the proposed configurable steering network are investigated for N= 4, 8, and 16. The results demonstrate the capability of the proposed configurable beamsteering network in controlling the steering angle of the designed PAAs.