Antenna Measurement System using Radio over Fiber Transceiver with Vector Network Analyzer up to 6 GHz

S. Kurokawa*1, M. Hirose1, Y. Toba2, J. Terakado2 M. Onizawa2, and J. Ichijo2 1 National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan

2 Seiko Giken Co., Ltd., Chiba, Japan

Abstract - We newly develop an antenna measurement

system using radio over fiber transceivers with vector network analyzer. Our proposed system can extend the port of vector network analyzer using optical devices and optical fibers up to 6 GHz. Our proposed system can measure S-parameters in full 2-port calibration from 1 to 6GHz with 60 dB dynamic range. In this paper, we show outline of our developed system. Further, we demonstrate the antenna measurement for double ridged guide horn antenna.

Index Terms — Antenna measurement system, radio over fiber transceiver, antenna gain, double ridged guide horn antenna, S-parameter, vector network analyzer.

1. Introduction

Radiated EMI (Electromagnetic Interference) measurement need to measure the radiated electromagnetic field intensity using broadband antennas up to 6 GHz or 18 GHz [1]. Further, Recent progresses in wireless communication technologies are remarkable for broadband wireless internet and mobile communication systems. Conventional antenna measurement system usually uses metal coaxial cables. The system has some problems, such as the attenuation of signals in the cables, the reflection waves on the outside surface and the difficulty of its handling. For this reason, we have already developed an antenna measurement system using bi-directional type radio over fiber (RoF) transceiver with vector network analyzer (VNA) up to 3 GHz [2]. Our previous proposed system can measure s-parameter in full 2-port calibration. To improve the frequency range, we newly developed bi-directional type RoF transceiver up to 6 GHz. Our system can eliminate the unwanted influence of coaxial cables and decrease the attenuation of microwave signal.

In this paper, we explain our proposed system. At first, we explain the outline of our proposed system. Second, we explain the performance of the system in full 2-port calibration of VNA. Finally, we demonstrate the antenna gain measurement using our proposed system.

2. Outline of our proposed system

Figure 1 shows the outline of bi-directional type RoF transceiver with VNA. A transmitting port of our transceiver connects to source output port 1 of VNA, a receiving port of our proposed transceiver connects to A-channel of port 1 of VNA, a transmitting port of our transceiver connects to source output port 2 of VNA, and receiving port of our

proposed transceiver connects to B-channel of port 2 of VNA. Then, our proposed transceivers connect to the transceivers for device under measurement by optical fibers.

Fig. 2 shows measured dynamic range of S21(ω) using our system with step attenuator in full 2-port calibration using the electrical calibration module. S-parameters are measured by PNA E8358A vector network analyzer of Keysight technology Inc.. The frequency range, the frequency interval, and the IF frequency of the VNA are from 1 MHz to 9 GHz, 1 MHz, and 100 Hz, respectively. [ATT= x dB] indicates the measurement frequency response for the case of ATT= x dB attenuation. These results show that the dynamic range of our system is more than 60 dB in the frequency range from 500 MHz to 6 GHz.

Fig. 1. Our newly proposed optical fiber link port extender with VNA.

Fig. 2 Dynamic range of our proposed system with VNA.

Directionalcoupler

Optical fiber coupler

Photodiode

Direct modulation Laser diode

Microwaveamplifier

Microwaveamplifier

Photo Diode

DirectmodulationLaser Diode

Optical fibercoupler

Microwaveamplifier

Microwaveamplifier

Sour

ce o

ut 1

Sour

ce o

ut 2

Vector Network Analyzer

Photo Diode

DirectmodulationLaser Diode

Optical fibercoupler

Microwaveamplifier

Microwaveamplifier

D U T

Directionalcoupler

Optical fiber couplerPhoto

diode

Direct modulation Laser diode

Microwaveamplifier

Microwaveamplifier

Input BInput A

2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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Fig. 3 Standard deviation of measured | S21(ω)|.

3. Antenna gain measurement for double ridged guide horn antenna

In order to demonstrate the validity of our proposed optical fiber link transceiver with VNA, we carry out the antenna measurement of double ridged guide horn antenna (DRGH) 3115 of ETS-Lindgren Inc. [3] in full 2-port calibration of VNA. Two DRGH set face to face at antenna distance 3.75 m. S-parameters (S11(ω), S21(ω), S12(ω), S22(ω)) are measured by our proposed system with VNA. Fig 4, 5, 6 and 7 show measured S21(ω) magnitude, calculated S21t(t) envelope, measured S22(ω) magnitude and calculated S22t(t) envelope using our proposed system with 30 m coaxial cable. In these figures, [RoF and 30 m optical cable] with blue dotted line indicates measured results using our proposed RoF systems and 30m coaxial cable with VNA. [10 m coaxial cable] with red solid line indicates measured results using 10m coaxial cable with VNA. Difference of measured S21(ω) magnitude between them is less than 0.5 dB in the frequency range from 0.5 GHz to 6 GHz except around 5.5 GHz. In the case of using proposed coaxial cable, S21t(t) has multireflection wave between two DRGHs around 50 ns. However, In the case of using our proposed RoF system, S21t(t) has no multireflection wave between two DRGHs around 50 ns. Difference of measured S22(ω) magnitude between them is less than 1.5 dB in the frequency range from 0.5 GHz to 6 GHz except around 5 to 5.5 GHz. In the case of antenna gain measurement, we must eliminate the multireflection waves from the estimated S21t(t)s. These results show the fact that our proposed system can measure S21(ω)s with no multireflection waves without elimination techniques for the measured S21(ω)s.

Fig. 4 Measured S21(ω)s of two DRGHs using proposed system with 30 m optical cable and 10 m coaxial cable at antenna distance D=3.75 m.

Fig. 5 Measured S21t(t)s envelope of two DRGHs using proposed system with 30 m optical cable and 10 m coaxial cable at antenna distance D=3.75 m.

Fig. 6 Measured S22(ω)s of two DRGHs using proposed system with 30 m optical cable and 10 m coaxial cable at antenna distance D=3.75 m.

-5 0 5 10 15 20 25 30Time (ns)

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RoF and 30 m optical cable10 m coax cabble

Fig. 7 Measured S22t(t)s of DRGH using proposed RoF transceivers with VNA at antenna distance D=3.75 m.

4. Conclusion

In this paper, we develop the antenna measurement system using bi-directional radio over fiber transceivers with VNA. Our proposed system can measure S-parameters in full 2-port calibration up to 6 GHz with 60dB dynamic range.

References [1] CISPR 16-1-4:2010 Specification for radio disturbance and

immunity measuring apparatus and methods - Part 1-4: Radio disturbance and immunity measuring apparatus - Antennas and test sites for radiated disturbance measurements

[2] S. Kurokawa, M. Hirose, Y. Toba, M. Onizawa, and J. Ichijo, `` Optical Fiber Link Port Extender for Vector Network Analyzer,’’ in Proc. 32nd URSI GASS, Aug. 2017.

[3] Double-Ridged Guide Antenna, ETS-lindgren Inc., http://www.ets-lindgren.com/3115

2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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