ETS 5 (Engineering Test Satellite), renamed Kiku 5 in orbit, was launched to confirm H-1 UM-129A launch vehicle performance, as well as to establish basic geostationary three-axis bus system technology for future satellite applications, amass independent technology required for next-generation satellite development and carry out experiments for mobile communications satellites.

Kiku-5 finished its 1.5-year programmed operation on March 31, 1989, while AMEX (Aeronautical Mobile Experimental Transponder) continued gathering data and carrying out experiments.

This experimental system uses radio wave of L - band (1.6 GHz for uplink and 1.5 GHz for downlink) between mobile bodies and the satellite. and C - band (6 GHz for uplink and 5 GHz for downlink) between satellite and coast/aerial earth stations.
L-band antenna possesses a two-beam structure consisting of N-beam to irradiate northern parts of the Pacific Ocean Region including all of Japan and S-beam to irradiate southern parts of the Pacific Ocean Region. Basic communication circuits undergoing experiments are C/ L, L/C circuits between coast/aerial earth stations and mobile bodies, but experiments on mutual L/L circuits between mobile bodies and C/ C circuit for ranging satellites are also carried out.
Mobile satellite communications using a two-beam antenna is the first try in Japan, and it is expected that the experiments with AMEX will lead to their application in various fields of communication.