Broadband Sub-THz Chirp Linearization Using Particle Swarm Optimization for Precision Metrology Applications

This paper demonstrates the precise linearization of a broadband sub-THz FMCW chirp via a particle swarm optimization technique to enable extremely high-resolution and accurate range measurements. A detailed explanation of the implemented particle swarm optimization is presented. The frequency chirp has 66.7GHz bandwidth from 191GHz to 257.7GHz with a standard deviation of 241KHz, relative to linearity. We show that this chirp has an accuracy of 61µm in the range of 61cm, which is equivalent to a 0.01 % range error. We also illustrate that the linearized chirp holds its linearity for large range target displacements. This accuracy level is beneficial to industrial metrology applications like small defect detection on highly smooth surfaces.

I. Introduction

Frequency-Modulated Continuous-Wave (FMCW) radars with broad bandwidth have unique applications in the fields of imaging [1]–[3], spectroscopy [4], and metrology [5]–[8]. The spatial range resolution in FMCW imaging radars depends inversely on radar bandwidth, , through the relation , where is the speed of light: the broader radar bandwidth, the finer spatial cells. However, achieving the ultimate range resolution requires the radar's frequency change in time in an extremely controlled and predictable manner.