We have developed an all-optical fiber link antenna measurement system for a millimeter wave 5th generation mobile communication frequency band around 28 GHz. Our developed system consists of an optical fiber link an electrical signal transmission system, an antenna-coupled-electrode electric-field (EO) sensor system for 28GHz-band as an electrical signal receiving system, and a 6-axis vertically articulated robot with an arm length of 1m. Our developed optical fiber link electrical signal transmission system can transmit the electrical signal of more than 40GHz with more than -30dBm output level. Our developed EO sensor can receive the electrical signal from 27GHz to 30GHz. In addition, we have estimated a far field antenna factor of the EO sensor system for the 28GHz-band using an amplitude center modified antenna factor estimation equation. The estimated far field antenna factor of the sensor system is 83.2dB/m at 28GHz.

In the microwave band, Optical Electric Field Sensors (OEFS) provide an attractive method to measure electromagnetic fields precisely. It is difficult however, to develop an OEFS that operates with both wide bandwidth and high sensitivity. In this paper, we propose a Log-Periodic Dipole antenna Array (LPDA)-type OEFS that achieves high sensitivity over a wide bandwidth. The LPDA-type OEFS has a large number of electrodes that are attached to each of the antenna elements. Not only the lengths of the antenna elements but also the lengths of electrodes vary log-periodically. The OEFS responds to microwaves by synchronizing the propagation direction of light with the propagation direction of the microwave. An OEFS constructed of y-cut z-propagation Lithium Niobate (LN) demonstrates good stability against temperature variation. Theoretical analysis with respect to the refractive index variation and optical modulator with the crystal orientation will be provided in this paper. In addition, the characteristics of the proposed LPDA-type OEFS will be shown over wide bandwidth in the microwave band.

An electric filed sensor using Mach-Zehnder interferometers has been designed to operate more than 10 GHz. The velocity of optical wave on the waveguide is investigated to determine the electrode length, and the characteristics of frequency response are analyzed using the moment method to determine the sensor element length. The electrode length of 1 mm and the element length of 8 mm are settled by these investigations. An isotropic electric field sensor is constructed using three sensors. The minimum detectable electric field strength is 22 mV/m at frequency bandwidth of 100 Hz. This is about 100 times for the conventional electric field sensor using the similar element. The sensitivity deviation is within 3 dB when temperature changes from 0 degree to 40 degree. The deviation of directivity can be tuned within 1 dB to calibrate the sensitivity of the each element. The sensitivity degradation is within 6 dB up to 5 GHz and within 10 dB up to 10 GHz. This is almost agree with the calculated results. The sensor can measure almost the same waveform as the applied electric field pulse whose width is 6 ns and rise time is less than 2.5 ns.

The design method for sensitivity and frequency response of an electric field sensor using a Mach-Zehnder interferometer (an optical E-field sensor) has been developed in order to measure electromagnetic environments and the performance of measuring facilities. The designs of the optical modulator, sensor elements, and sensitivity were analyzed theoretically by using an accurate equivalent circuit of the sensor. Then an actual sensor was fabricated, and its characteristics of the sensor were evaluated experimentally. The results show that the designed sensitivity and frequency response were optimal. The optical output deviation when the temperature increased from 0 to 40 was reduced to within 2 dB. The minimum detectable electric field strength was 17 dBµV/m (8 µV/m), and the dynamic range was more than 100 dB. The frequency response of the sensitivity was almost flat between 200 Hz and 900 MHz.

Recent progress in electromagnetic compatibility (EMC) technology has created a need for small and wideband antennas that can be used to measure the quality of EMC measurement facilities and to measure electric field strength for immunity tests and human hazard studies. Antennas using fiber optics are being developed because this kind of antenna has the wideband property and can eliminate the influence of the coaxial cable. This paper first summarizes the development of fiber optic antennas for EMC measurement and the construction of practical fiber optic antennas. It then describes the recent progress that has been made in Japan. This progress includes the electromagnetic source and the electric field sensor using a spherical dipole antenna with O/E or E/O converters, and it includes a wideband electric field sensor using electro-optical crystals.