2.65 Gbps downlink communications with polarization multiplexing in X-band for small earth observation satellite

Tomoki Kaneko, Noriyuki Kawano, Yuhei Nagao, Keishi Murakami, Hiromi Watanabe, Makoto Mita, Takahisa Tomoda, Keiichi Hirako, Seiko Shirasaka, Shinichi Nakasuka, Hirobumi Saito, Akira Hirose

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


This paper reports our new communication components and downlink tests for realizing 2.65 Gbps by utilizing two circular polarizations. We have developed an on-board X-band transmitter, an on-board dual circularly polarized-wave antenna, and a ground station. In the onboard transmitter, we optimized the bias conditions of GaN High Power Amplifier (HPA) to linearize AM-AM performance. We have also designed and fabricated a dual circularly polarized-wave antenna for low-crosstalk polarization multiplexing. The antenna is composed of a corrugated horn antenna and a septum-type polarizer. The antenna achieves Cross Polarization Discrimination (XPD) of 37 - 43 dB in the target X-band. We also modify an existing 10 m ground station antenna by replacing its primary radiator and adding a polarizer. We put the polarizer and Low Noise Amplifiers (LNAs) in a cryogenic chamber to reduce thermal noise. Total system noise temperature of the antenna is 58 K (maximum) for 18 K physical temperature when the angle of elevation is 90 on a fine winter day. The dual circularly polarized-wave ground station antenna has 39.0 dB/K of Gain - system-noise Temperature ratio (G/T) and an XPD higher than 37 dB. The downlinked signals are stored in a data recorder at the antenna site. Afterwards, we decoded the signals by using our non-real-time software demodulator. Our system has high frequency efficiency with a roll-off factor α = 0.05 and polarization multiplexing of 64APSK. The communication bits per hertz corresponds to 8.41 bit/Hz (2.65 Gbit/315 MHz). The system is demonstrated in orbit on board the RAPid Innovative payload demonstration Satellite (RAPIS-1). RAPIS-1 was launched from Uchinoura Space Center on January 19th, 2019. We decoded 1010 bits of downlinked R- and L-channel signals and found that the downlinked binary data was error free. Consequently, we have achieved 2.65 Gbps communication speed in the X-band for earth observation satellites at 300 Mega symbols per second (Msps) and polarization multiplexing of 64APSK (coding rate: 4/5) for right- and left-hand circular polarizations.

Original languageEnglish
Pages (from-to)1-12
Number of pages12
JournalIEICE Transactions on Communications
Issue number1
Publication statusPublished - 2021 Jan


  • Cross Polarization Discrimination (XPD)
  • DVB-S2X
  • Polarization multiplexing
  • Satellite communications
  • Small satellite

ASJC Scopus subject areas

  • Software
  • Computer Networks and Communications
  • Electrical and Electronic Engineering


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