# A Circularly Polarized Broadband Composite Spiral Antenna for Ground Penetrating Radar

## TL;DR

A new spiral antenna improves ground-penetrating radar's ability to detect underground objects by using circular polarization and wideband performance.

## Contribution

A novel composite spiral antenna design combining equiangular and Archimedean spirals for enhanced GPR performance is introduced.

## Key findings

- The antenna achieves 1–5 GHz wideband coverage with stable circular polarization.
- Axial ratio remains below 3 dB across the frequency band, ensuring good polarization performance.
- 3D GPR measurements show improved detection of subsurface linear objects compared to conventional antennas.

## Abstract

To enhance the capability of a ground penetrating radar (GPR) in subsurface target identification and improve its polarization sensitivity in detecting underground linear objects, a circularly polarized broadband composite spiral antenna was designed. This antenna integrates equiangular spiral and Archimedean spiral structures, achieving a wideband coverage of 1–5 GHz with stable circular polarization characteristics. The antenna employs an exponentially tapered microstrip balun for impedance matching and a metallic-backed cavity filled with absorbing materials to enhance its directivity. Experimental results demonstrate excellent radiation performance and stable circular polarization characteristics, with the axial ratio consistently below 3 dB throughout the operating frequency band, highlighting its suitability for polarimetric GPR systems. Furthermore, a 3D GPR measurement using the designed antenna validates its improved capacity for detecting subsurface linear objects, compared to the conventional linearly polarized bowtie antenna.