Research and development on 20 GHz Digital Radio-Relay system

Structure of transmitter local oscillator

Fig.1 Structure of transmitter local oscillator

Cross-polarization discrimination (XPD) degradation due to rainfall

Fig.2 Cross-polarization discrimination (XPD) degradation due to rainfall

Standard relay station general view

Fig.3 Standard relay station general view

    Microwave radio-relay system has been employed to cope with the rapidly increasing transmission demand for the subscriber toll dialing network and television program relay network in the Nippon Telegraph & Telephone Co. by using microwave spectrum below 15 GHz including 2,4,5,6 and 11. However, further large capacity and economical digital radio-relay system was required for the forthcoming total communication network to treat the diversification of the new services.

    Newly developed 20GHz digital radio-relay system is enabling long distance digital transmission of 5,760 telephone channels (400Mbit/s) per radio channel and about 46,000 telephone channels per total radio system utilizing unexplored new frequency spectrum.

    Research and development activities required about eight years and cooperation of wide range experts in NTT Co. and manufacturing industries was required. Particularly, Moriji Kuwabara, Heiichi Yamamoto and Yoshio Nakamura played a key role overcoming difficulties in different stage of the research and development. A great many technical difficulties in exploiting the so-called quasi-millimeter wave spectrum of 20 GHz arose from the severe radio attenuation due to rainfall and innovative activity was required.

    Feasibility study of this system was begun in 1969 and several on-site field tests were conducted in Kanto and Hokuriku district in order to find and reveal every subject and problem under real environmental condition. Total system examination was conducted in Yokosuka area in 1974. Commercial service on Tokyo-Yokohama and Osaka-Kobe sections was successfully started in December of 1976.

    Realization of this system depend on the following technical establishment: (1) highly accurate presumption of radio attenuation and clarification of cross-polarization discrimination deterioration mechanism in the 20 GHz frequency band due to heavy rainfall, (2) jitter reduction method in multiple relaying, (3) high-speed and spectrum-efficient QPSK modulator with inter-symbol interference compensation, (4) small and high-reliable electric circuit, such as solid-state quasi-millimeter wave oscillator, microwave IC and ring-type branching-filter, (5) economic pillar type relay station with workability and maintainability. This system has been steadily operated since the start of service and it was confirmed its original objectives have been fully achieved.

    Completion of this system gave the basis for formation of the future digital transmission network, further increased the level of this technical area.

    The Institute of Electronics and Communication Engineer awarded the Achievement Prize for this technology to Yoshio Nakamura, Heiichi Yamamoto and Moriji Kuwabara in 1978.


[1] Yoshio Nakamura, Tatuo Yoshikawa, Heiichi Yamamoto, Kohei Nishino, and Akira Hosoda、20 GHz Digital Radio-Relay System、1978、Journal of IECE, Vol.61, No.3, 1978/3
[2] Kenji Kohiyama and Kouji Monma、Band Reflection Type Cavity Stabilized Gunn Oscillator、1974、Trans. IECE, Vol.57-B, No.2, 1974/2
[3] Heiichi Yamamoto and Hiroaki Shiota、PIN-Diode High-Speed Quadriphase Modulator at 20 GHz Band、1975、Trans. IECE, Vol.58-B, No.7, 1975/7
[4] K. Morita et al.、Measurement of Cross-Polarization Distortion in 20GHz Band due to Rain、1974、Trans. IECE, Vol.57-B, No.9

Related Researches



Events in World

Japan-China Peace and Amity Treaty was signed.
Narita Airport was inaugurated.
Page Top