# Experimental demonstration of spectrally-broadband Huygens sources using low-index spheres

## TL;DR

This paper experimentally demonstrates a broadband Huygens' source using low-index dielectric spheres that achieve forward scattering with suppressed backscattering over an octave spectral range at GHz frequencies.

## Contribution

It introduces a practical method to realize broadband Huygens' sources with low-index spheres, expanding design options without magnetic materials.

## Key findings

- Achieved forward scattering over more than an octave bandwidth.
- Demonstrated suppression of backscattering in low-index spheres.
- Provided design guidelines for broadband Huygens' sources.

## Abstract

Manipulating the excitation of resonant electric and magnetic multipole moments in structured dielectric media has unlocked many sophisticated electromagnetic functionalities. This article demonstrates the experimental realization of a broadband Huygens' source. This Huygens' source consists of a spherical particle that exhibits a well-defined forward-scattering pattern across more than an octave-spanning spectral band at GHz frequencies, where the scattering in the entire backward hemisphere is suppressed. Two different low-index nonmagnetic spheres are studied that differ in their permittivity. This causes them to offer a different shape for the forward-scattering pattern. The theoretical understanding of this broadband feature is based on the approximate equality of the resonant electric and magnetic multipole moments in both amplitude and phase in low permittivity spheres. This is a key condition to approximate the electromagnetic duality symmetry which, together with the spherical symmetry, suppresses the backscattering. With such a configuration, broadband Huygens' sources can be designed even if magnetic materials are unavailable. This article provides guidelines for designing broadband Huygens' sources using low-index spheres that could be valuable to a plethora of applications.