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not uniform as shown in Fig.10. A 300 GHz-band signal generator was used to transmit an unmodulated continuous wave, and a spectrum analyzer received the signal for propagation loss analysis. e communication distance was changed by relocating the Rx station against the xed Tx station, and the receiving power was measured up to 22 m away. Two horn antennas (gain 25 dBi, beam-width 10°) were used at TX and RX, and the TX output power was set to -15 dBm. Both antennas were installed at a height of 215 cm from the oor. Figure 11 shows the plots of measured path loss characteristics by calculating from received power. A straight-line approximation is also overlaid in the gure. e path loss model used in this approximation is based on the model of ITU-R P.1238. Assuming theoretical propagation loss L0 = 82 dB at the reference distance 1 m, the least-squares regression line of the data resulted in a pass loss coecient value of N=20.2, which is slightly larger than the free space path loss (N=20). In some TX and RX spatial arrangements, measured data points were away from the straight-line approximation. is was indi-cating the eect of reection especially in the congurations in which both the transmitter and receiver are located near a server chassis. To examine the variations of propagation loss (or height pattern characteristics) more closely, the TX and RX antennas were positioned in two dierent spatial arrangements as shown in Fig.12: one with a server chassis positioned on the specular reection point, and the other o the point. e results showed clear dierence between the two cases: the one in which the receiver received the direct path only, and the other in which the receiver re-ceived waves reected from the server chassis in addition to the direct path. is indicates the importance of two parameters — i.e. distances between the server chassis and height of the antennas — for the optimum design of inter-server wireless communication. Numerical calculation us-ing the ray-tracing method also made clear that the cause of dierent behavior can be ascribed to the reected waves from the server chassis. e authors conducted additional propagation measurements in oce and corridor environ-ments, and combined all the results into a contribution document, which was submitted to ITU-R SG3 WP3K for review. e proposed model was approved in the working group and has been included in ITU-R Recommendation P.1238 (prediction and evaluation method for indoor, short-distance propagation loss).4SummaryFor designing wireless applications using millimeter-wave and terahertz-wave, the rst step is to know the radio propagation characteristics. To clarify the radio propaga-tion characteristics contributes to the further development of radio communication, and it is a part of our mission. Developed propagation models will be a useful tool for designing specic future radio communication systems.AcknowledgmentsWe would like to extend our deep appreciation to Mr. Nobuhiko SHIBAGAKI and Mr. Mitsuru WATANABE (Hitachi, Ltd), Mr. Kunihiro KAWASAKI, Mr. Kazuki NAKAMURA and Mr. Nagateru IWASAWA (Railway Technical Research Institute) for providing us with propagation measurement data for our research on railway radiocommunication systems. We also thank our colleagues in NICT, Dr. Katsumi FUJII (Research Manager), Dr. Akifumi KASAMATSU (Executive Researcher) and Dr. Hiroyo OGAWA (Technical Researcher) for giving us valuable advice throughout the course of our terahertz wave propagation study. A part of this study was conducted under the auspices of the Ministry of Internal Aairs and Communications (contract research toward extended use of radiowave resources).FiF12　Validation of measurement result by ray-tracing method(Copyright(C)2017 IEICE, [4] Fig. 12)501001502002503008090100110RX antenna height from server top (mm)Path loss (dB) Measurement Ray-tracingTXCeilingRX positionDirect pathregionDirect and reflect paths region232-3 Study on Propagation Model for Advanced Utilization of Millimeter- and Terahertz-Waves