Two-Dimensional Fiber Beamforming System Based on Mode Diversity

Abstract

In this paper, a novel two-dimensional (2D) beamforming system based on mode diversity and true-time delay (TTD) of optical fiber is proposed. The system is composed of two cascaded TTD units, which are single-mode fiber TTD line array and mode TTD line array of few-mode fiber. For the first time, the mode diversity technology is applied to the 2D beamforming system which can realize beam scanning at a single wavelength and greatly reduces the cost and complexity. A beamforming system with <inline-formula> <tex-math notation= LaTeX >$3\\times 3$ </tex-math></inline-formula> array antenna is built, and the properties of which are experimentally evaluated under a single wavelength of 1550.52 nm. The azimuth and elevation angles can reach the scanning range of ±60°. The gain performance are characterized, which decreases about 6 dB when the angle changes from <inline-formula> <tex-math notation= LaTeX >$(0.11^{\\circ }, -0.11^{\\circ })$ </tex-math></inline-formula> to <inline-formula> <tex-math notation= LaTeX >$(59.82^{\\circ },60.21^{\\circ })$ </tex-math></inline-formula> or <inline-formula> <tex-math notation= LaTeX >$(-59.25^{\\circ }, -60.02^{\\circ })$ </tex-math></inline-formula>. The influence of frequency and mode coupling on the system performance are evaluated. The beam direction of the system is independent of microwave signal frequency while the test scope is 8.5 GHz to 11.5 GHz. Mode coupling has no effect on the beam direction of the system.