Using optical switches and fiber delay lines for wideband beamforming with RF uniform linear antenna arrays

We investigate the use of optical switches and fiber delay lines to provide true time delays for ultra-wideband beamforming with RF uniform linear antenna arrays. In our approach, we use the received RF signals to amplitude modulate lasers of distinct wavelengths, pass the optical signals through optical switches and fiber delay lines, and combine the delayed signals before detection. Since it is impossible to provide fiber delay lines at all lengths, we investigate how to quantize delay values subject to the constraint on the inefficiency inflicted on the user power. In addition, we construct an efficient architecture for a delay line switching network that uses the minimum number of switch ports to provide the delays for beamforming.

1. Introduction

The use of antenna arrays instead of a single antenna provides benefits in several wireless applications including diversity against fading, interference rejection, and frequency reuse. Recently, there is strong interest in ultra-wideband applications (with bandwidth of the center frequency) such as spread sprectrum, high data rate satellite, and high-resolution sensor systems. We shall use the term “wideband” to describe such systems in what follows. Most existing array processing techniques rely on the narrowband assumption. While it is possible to split wideband signals into narrowband components and use narrowband signal processing, the cost for doing so is expensive.