Contents I. Introduction
Real time foreign object debris (FOD) detection systems for airport runways, which use radio over fiber (RoF) radars connected to a base station through an optical fiber network, have been developed [1]. Due to low atmospheric attenuation, these systems use 90-GHz band FMCW radar signal to detect small signals with high spatial resolution. We developed a zero-bias operational UTC-PD integrated RF amplifier, operating in the range of 80–110 GHz, and the photoreceiver units were coupled to distributed rotary antennas for searching FODs on runway surfaces. Compared to rotary type antennas, phased array antennas are preferable from the perspectives of high scanning capability and long life, because the antenna units would be fixed for beam formation. To realize the advanced RoF radar system with an optical phased array circuit using UTC-PD (see Fig. 1), the high spatial resolution 90-GHz near/far-electric fields on small-size patch antennas should be measured and analyzed for precise phase control. For this, a THz probe, which is capable of detecting 1- or 2-dimensional THz signals and has a small probing head of around 1 mm, is an ideal candidate. In our previous work, we developed a compact THz probe system using ZeTe crystal for high-speed EO sampling [2], which could detect optical signals of up to 2 THz. In this study, we demonstrate the detection of a W-band signal (80 GHz) near the antenna surface using a THz probing system, by assuming an advanced phased array antenna set-up coupled to an RoF radar system.
Schematic configuration of optical phased array for beam steering,
