Fujitsu's Millimeter-band Transmitter Exceeds 10Gbps Data Transmission Speeds

(Top News, 23 Jun 2008)

Fujitsu Laboratories Ltd and Fujitsu Ltd have developed a transmitter operating in the 70GHz to 100GHz band using impulse radio that is capable of transmitting data at speeds of more than 10Gbps. This new development eliminates the need for oscillators and other hardware that had been required for use of earlier millimeter-band transmitters, thus enabling a smaller millimeter-band transmitter. As a substitute for fiber-optic high-speed lines, the new transmitter could be used in wide range of applications geared to help bridge the digital divide, including platform networks and short-range wireless LANs.

This research was carried out as part of the Research and Development Project for Expansion of Radio Spectrum Resources, which is sponsored by Japan's Ministry of Internal Affairs and Communications.

Fujitsu and Fujitsu Laboratories developed the following impulse-radio technologies to enable the transmitter to achieve 10Gbps data transfer speeds:
1. Ultra-short pulse generator
To obtain sufficiently high energy pulses in the 70GHz to 100GHz band, the pulses need to be very short. The smaller the full-width is at half-maximum (FWHM) for a pulse, the higher the energy it carries up to a high frequency; effectively, this requires a FWHM below 10 picoseconds (ps).

Fujitsu Laboratories' indium-phosphide high electron-mobility transistor (InP-HEMT) technology enabled the development of a short-pulse generator, with a FWHM of 7.6ps—proven to carry enough energy for frequencies above 100GHz.

2. Low-loss filter
The millimeter-band pulse transmitter carries energy in a short pulse across an extremely wide band, which must be able to extract only that band needed for transmission. Because the millimeter band is highly susceptible to losses caused by the skin effect, the researchers created a multi-stage coupled-line filter using a substrate of alumina, which is readily obtainable and offers excellent high-frequency performance.

The result is that the filter passes a signal frequency range of 78GHz to 93GHz, and losses within that range (insertion losses) were 1.5dB ±0.1dB, resulting in the levels of performance needed for a millimeter-band impulse radio transmitter.

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