Continuously tunable true-time delay lines based on a one-dimensional grating waveguide for beam steering in phased array antennas.

Abstract

In this paper, we propose integrated one-dimensional (1D) grating waveguide-based true-time delay (TTD) lines on a silicon-on-insulator (SOI) platform. Through optimizing the structure of the proposed waveguide, a time delay of 77.23ps/mm can be readily achieved in a wavelength tuning range from 1540.20nm to 1558.97nm. Compared to conventional photonic crystal waveguide-based TTDs, the proposed waveguide occupies 70% less chip surface and has much lower propagation loss when compared with 2D photonic crystal devices. Therefore, a larger time delay can be achieved on-chip. To facilitate low loss coupling from strip waveguides to 1D grating waveguides and vice versa, a novel step taper is designed and shows a coupling efficiency of over 78%. Based on the 1D grating waveguide, a 1×4 beam steering module is designed and simulated. A wide beam steering angle from -67.84° to 67.84° for the X-band four-element phased array antenna with an array pitch size of 1.25cm is obtained.