Photonics-Based Near-Field Measurement and Far-Field Characterization for 300-GHz Band Antenna Testing

Yusuke Tanaka,Norihiko Sekine,Issei Watanabe,Guillaume Ducournau,Shintaro Hisatake,Frederic Gianesello,Akifumi Kasamatsu,Akihiko Hirata,Cyril Luxey,Cybelle Belem-Goncalves

doi:10.1109/ojap.2021.3133470

Abstract

In this study, photonics-based near-field measurement and far-field characterization in a 300-GHz band are demonstrated using an electrooptic (EO) sensor with planar scanning. The field to be measured is up-converted to the optical domain (1550 nm) at the EO sensor and delivered to the measurement system with optical fiber. The typical phase drift of the system is 0.46° for the one-dimensional measurement time of 13 s, which is smaller than the standard deviation of the phase measurement of 1.2° for this time scale. The far-field patterns of a horn antenna calculated from the measured near-field distribution are compared with that measured with the direct far-field measurement system using a vector network analyzer. For the angular related parameters, the accuracy of the results obtained by our near-field measurement are comparable to that of those obtained by direct far-field measurements. The sidelobe level discrepancy (approximately 1 dB) between the results obtained based on our near-field measurement and those from the direct far-field measurements are attributed to the excess noise of the probe correction data. We believe that photonics-based near-field measurements with spherical EO probe scanning will pave the way for the characterization of high-gain antennas at the 300-GHz band.

Highlights

I N recent years, the development of antennas operating in the upper limit of the millimeter-wave band or the lower limit of the terahertz (THz) band has become increasingly important due to the increasing need for high-capacity and -speed wireless communications in these frequency bands
Our system has the following features over conventional systems: (1) the probe head is small, and all the components, including the optical fiber, are made of dielectric material; the field disturbance to be measured is negligible; (2) the probe head is extremely light; the deflection of the scanner that holds the probe is negligible, enabling a high-fidelity pattern measurement; (3) the detected signal is transmitted to the measurement system via flexible and low-loss optical fibers; the system can accommodate large scan areas; and (4) the local oscillator (LO) signal is generated based on the photonics-based self-heterodyne technique [25], and the RF signal is detected based on a nonpolarimetric frequency downconversion technique [26], which is more stable than the conventional polarimetric technique [27]
We demonstrated the near-field measurement (NFM) and the far-field characterization at the 300-GHz band based on the photonicsbased system using the EO probe

Summary

INTRODUCTION

I N recent years, the development of antennas operating in the upper limit of the millimeter-wave band or the lower limit of the terahertz (THz) band has become increasingly important due to the increasing need for high-capacity and -speed wireless communications in these frequency bands. Our system has the following features over conventional systems: (1) the probe head is small (submillimeter order), and all the components, including the optical fiber, are made of dielectric material; the field disturbance to be measured is negligible; (2) the probe head is extremely light; the deflection of the scanner that holds the probe is negligible, enabling a high-fidelity pattern measurement; (3) the detected signal is transmitted to the measurement system via flexible and low-loss optical fibers; the system can accommodate large scan areas; and (4) the local oscillator (LO) signal is generated based on the photonics-based self-heterodyne technique [25], and the RF signal is detected based on a nonpolarimetric frequency downconversion technique [26], which is more stable than the conventional polarimetric technique [27] It can cover several hundreds of GHz frequency band with a high phase detection accuracy without changing the EO probe head [28]– [31]. The results suggest that accurate radiation patterns can be measured by the NFM system without any probe correction if spherical scanning is used

NFM System

NFM Algorithm

RESULTS AND DISCUSSION

CONCLUSION