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can be explained as that the RX beam of the APAA is corrected so as to maximize the gain in the Tsukuba direc-tion, and therefore the gain in the Kashima direction de-creases. Hence, in order to correct the phase of the receiving antenna of the APAA, it is necessary to transmit a test signal from Kashima.On the other hand, Figs. 26 and 27 show the results of receiving signals at Kashima terminal. e former shows the case where the beam was set using direction cosines and the latter shows the case where the beam was set using the compensation of the REV. As a result, the signal level received at Kashima is higher than the case when the beam was set using direction cosines by 0.23 dB, which implies improvement of gain. is can be explained that the gain in the Kashima direction improves by correction because the receiving earth terminal for the TX beam is in Kashima.7Conclusione application of the REV method to the WINDS APAA soundness verication has peculiar problems re-garding the on-board REV: the rotation timing of phase of elements at the REV of the satellite and the measurement timing of the earth terminal are not synchronous and the variation of the received signal level is large due to atmo-spheric uctuation. e former was solved by measuring twice during the same measurement period of phase set-ting, and the latter was solved by averaging 1,024 data points obtained from measurement and a smoothing pro-cess using the least-squares method.As a result of trend evaluation based on 19 measure-ments performed from October 9, 2008, to February 6, 2017, the amplitude and phase of all the elements were almost the same as those obtained at initial phase aer launch. ese results conrmed the soundness of the WINDS APAA. Also, a slight eect of improvement in gain was observed from the APAA phase compensation experi-ments.ReferenceR1S. Mano and T. Katagi, “A Method for Measuring Amplitude and Phase of Each Radiating Element of a Phased Array Antenna,” IEICE Transaction, vol.J65-B, no.5, 1982.2M. Yajima, T. Horiuchi, M. Nakano, A. Akaishi, M. Ohkawa, and T. Takahashi “Health Check Experiment of Active Phased Array Antennas on KIZUNA(WINDS) by Two Stations Simultaneous Measurement,” IEICE Technical Report, vol.111, no.7, SANE2011-7, 2011.Akira AKAISHI Space Communications Laboratory, Wireless Networks Research CenterSatellite communications systemMitsugu OHKAWA, Ph.D.Senior Researcher, Space Communications Laboratory, Wireless Networks Research CenterSatellite communications systemTakashi TAKAHASHI Associate Director, Space Communications Laboratory, Wireless Networks Research CenterSatellite communication1373-7 Experimental Reports of APAA Health Test