Quadrupole radiation from terahertz dipole antennas

Area of Science:

• Optics and Photonics
• Electromagnetics
• Antenna Theory

Background:

• Lens-coupled terahertz dipole antennas are crucial for terahertz (THz) applications.
• Understanding the polarization state of emitted radiation is essential for device performance and characterization.
• Previous studies have not fully detailed the polarization characteristics of these specific antenna types.

Purpose of the Study:

• To conduct the first detailed investigation into the polarization state of radiation emitted by lens-coupled terahertz dipole antennas.
• To characterize the nature and origin of any cross-polarized radiation components.
• To compare experimental findings with theoretical predictions.

Main Methods:

• Experimental measurement of the polarization state of terahertz radiation from lens-coupled dipole antennas.
• Analysis of the angular radiation pattern of both co-polarized and cross-polarized emission.
• Theoretical modeling using Fresnel-Kirchhoff scalar diffraction to calculate radiation patterns.
• Investigation of the role of photocurrent in feeding strip lines.

Main Results:

• A weak but measurable cross-polarized radiation component was detected, orthogonal to the primary dipole orientation.
• The angular radiation pattern of this cross-polarized emission was found to be quadrupolar, not dipolar.
• Theoretical calculations showed good agreement with the measured frequency-dependent angular distribution.

Conclusions:

• The study provides the first detailed characterization of cross-polarized emission from lens-coupled terahertz dipole antennas.
• The observed quadrupolar nature of cross-polarization is attributed to photocurrents in the antenna's feed lines.
• The findings enhance the understanding of terahertz antenna radiation mechanisms and support accurate theoretical modeling.