High Front-to-Back Ratio Dual-Polarized Antenna-Coupled Electrode Electro-Optic Modulator for 28 GHz Band Near Field Antenna Measurement

We have developed a simultaneously receiving type dual (orthogonally) polarized antenna-coupled-electrode electro-optic (EO) modulator for 28 GHz-band 5th generation mobile communication as a receiving antenna. Our developed EO modulator can measure the orthogonally polarized microwave signal simultaneously. Cross-polarization discrimination ratio for E-plane of the EO modulator is more than 18 dB, and Front to back ratio is more than 33 dB for the frequency range from 27 to 29.5 GHz, respectively. Further, we show a near field radiation patter measurement result for a WR-28 standard gain horn antenna using our developed EO modulator.

I. Introduction

5th generation mobile communication will use around 28 GHz frequency band in Japan [1]. For evaluating antenna radiation pattern for an antenna under test (AUT), we usually use an open-ended wave guide probe (OEWG) and a metal coaxial cable for a near field measurement [2]. In order to replace the coaxial cable and OEWG, we have already developed an antenna-coupled-electrode electro-optic (EO) modulator for 28 GHz-band 5^th generation mobile communication as a receiving antenna [3][4]. However, our developed EO modulator can only measure a single polarized wave. For receiving the orthogonally polarized near field radiation patterns simultaneously, we have newly developed a dual (orthogonally) polarized type EO modulator. The EO modulator has utilized a metal ground plane backed two antenna arrays and two LiNbO₃ optical phase modulators for receiving the orthogonally polarized two waves.