Micro-Doppler Frequency Comb Generation by Axially Rotating Scatterers

TL;DR

This paper presents a theoretical and experimental study of micro-Doppler frequency combs generated by axially rotating subwavelength scatterers, revealing a new spectral signature useful for target identification and space mapping.

Contribution

It introduces a novel analysis combining the Hallen integral equation and coordinate transformations to predict and observe micro-Doppler frequency combs from rotating scatterers.

Findings

Over ten peaks observed in the frequency comb.

Theoretical predictions match experimental results.

Potential applications in target identification and stellar radiometry.

Abstract

Electromagnetic scattering in accelerating reference frames inspires a variety of phenomena, requiring employment of general relativity for their description. While the quasi-stationary field analysis could be applied to slowly-accelerating bodies as a first-order approximation, the scattering problem remains fundamentally nonlinear in boundary conditions, giving rise to multiple frequency generation (micro-Doppler shifts). Here a frequency comb, generated by an axially rotating subwavelength (cm-range) wire and split ring resonator (SRR), is analyzed theoretically and observed experimentally by illuminating the system with a 2GHz carrier wave. Highly accurate lock in detection scheme enables factorization of the carrier and observation of more than ten peaks in a comb. The Hallen integral equation is employed for deriving the currents induced on the scatterer at rest and a set of coordinate transformations, connecting laboratory and rotating frames, is applied in order to predict the spectral positions and amplitudes of the frequency comb peaks. Unique spectral signature of micro-Doppler shifts could enable resolving an internal structure of the scatterers and mapping their accelerations in space, which is valuable for a variety of applications spanning from targets identification to stellar radiometry.