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Futuristic Glass Antenna by NTT Docomo and AGC

For nearly a year, NTT Docomo has been working with the glass manufacturer AGC to create a new transparent antenna that can work with a base station to become an antenna. We know that as we move towards higher frequency, the penetration of radio waves in building is affected. While this is not obvious in C band, it is very visible in case of mmWaves.

In a recent publication titled "An Unobtrusive Antenna", Osamu Sawaji interviewed NTT Docomo and AGC engineers about this development

To solve these problems, NTT DOCOMO entered into joint development with major glass manufacturer AGC, presenting a new glass antenna in November 2018. The antenna is 85 cm wide, 21.2 cm high and 6.6 mm thick, and on first glance appears to be normal transparent glass. However, the antenna becomes a base station when connected to cables and a wireless transceiver in the ceiling and attached to indoor window glass.

The antenna makes use of the laminated glass manufacturing technique used for the front windshield in cars. For laminated glass, resin is put between two sheets of regular glass and melted at high temperature, forming a single piece of glass. The glass antenna is made from the unified transparent resin and conductive materials that are placed between the two sheets of glass. In this way the glass becomes an antenna that can send and receive signals by conducting electricity. 

Moreover, a newly developed Glass Interface Layer (GIL) applied to the surface of the glass antenna reduces the signal attenuation and reflection that normally occurs when passing through window glass. The thickness of window glass varies according to window size and building floor height and normally affects the amount of signal attenuation and reflection, but by selecting the appropriate type of GIL, signals can be sent and received seamlessly no matter the size of the window glass the antenna is installed on.

Plans for commercialization of the glass antenna are now in the works and many inquiries have been received not just from Japanese mobile phone companies but also from companies overseas.

NTT DOCOMO and AGC are investigating the development of a glass antenna compatible with 5G, the next generation system of mobile communications. 5G will enable large amounts of data to be transmitted at very fast speeds, but the 5G signal has the disadvantage of being susceptible to attenuation from buildings, the atmosphere, rain and other obstacles.

NTT Docomo has been working with AGC and Ericsson to show demos of on-glass antennas on windscreen. The playlist for that is embedded below

Back in May, NTT Docomo also announced that they, in partnership with AGC and Ericsson have achieved what is believed to be the world's first 5G mobile telecommunications using an antenna embedded in synthetic fused silica glass to transmit and receive 28 GHz 5G radio signals for stable, high-speed mobile communication in buildings, vehicles and trains.

The antenna was used to verify 28 GHz 5G mobile communication with downlink speeds averaging 1.3 Gbps within a 100-meter range and reaching a maximum of 3.8 Gbps at 400 MHz. The verification tests, which used a vehicle fitted with multiple antennas and traveling about 30 km/h, were conducted in the Sumida area of Tokyo between April 22 and May 28.

Radio signals in the 28 GHz band are more linear than 4G LTE signals, so they are not strong enough to adequately penetrate windows in buildings, vehicles and railway cars. The new glass antenna can be attached to window surfaces to enable radio waves to be received and relayed in ideal directions for stable, high-speed 5G communications under challenging indoor and in-vehicle conditions.

In the latest NTT Docomo Technical Journal (October 2019 - Japanese Version), NTT Docomo have provided more details and trial results of this 5G glass antenna.

As can be seen in the table, in the on-glass antenna experiment using 800MHz bandwidth, A throughput of up to 7.9 Gbps ​​downstream was achieved. The average throughput is 3 Gbps in an area of ​​about 100m radius.The maximum distance was about 232m.

In the experiment with a integrated-glass 5G antenna, a 400MHz bandwidth and an 800MHz bandwidth were used. Up to 3.8Gbps downstream with 400MHz bandwidthwas achieved with 1.3 Gbps on average in an area with a radius of about 100m. Up to 7.5 Gbps downlink with 800 MHz bandwidth was obtained with 2.5 Gbps in an area with a radius of about 100m. The maximum communication distance was 178m.

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A new article on this topic is available from NTT Docomo in the January 2020 Technical Journal here.

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