Ultrashort Pulse Lasers Lead The Way For 5G

The lower the frequency, the larger the antenna must be. Conversely, tiny, exact antenna modules are required for the highest frequencies.

FREMONT, CA: 5G antenna modules are presently being added to cell towers. These modules are 64 working antennas whose radiation intersection ensures optimum spatial coverage. In the trade, this is familiar as massive multiple-input multiple-output(MIMO). However, massive MIMO also forms the opposite picture: MIMO-compatible antennas are necessary so smartphones, autonomous vehicles, and Industry 4.0 systems can work in the 5G network.

These are greatly complex modules with 16 and more individual antennas. The modules allow mobile devices and systems to use the signals from various transmitters concurrently, increasing the transmitted data rates significantly with no difference in transmission performance.

But there are disputes: 5G networks work with diverse gigahertz millimeter wave (GHz mmWave) frequencies. The spectrum ranges from 3.3 - 77 GHz. The lower the frequency, the larger the antenna must be.

Conversely, tiny, exact antenna modules are required for the highest frequencies. However, problems are inevitable with the combination of small antennas and GHz mmWave frequencies. For instance, the fingers and hands of smartphone users can block data transfer.

Three and more antenna modules per smartphone

To conquer these challenges – in other words, to ensure robust MIMO data transfer in various frequencies—smartphone manufacturers will install at least three antenna modules in different areas of their 5G devices. Naturally, this significantly increases the demand for antenna modules.

In addition, other challenges are involved in manufacturing the very complex, sometimes 3-dimensional 5G antennas. “The greater the frequency, the finer the structures of the antennas must be,” is how LPKF Laser & Electronics AG details the fundamental situation. The company provides a laser direct structuring process with which it is possible to attach any shape of the antenna, conducting paths, or insulation channels in resolutions to 25 micrometers (µm) directly onto three-dimensional plastic components.

The antennas are made from laminated substrates consisting of a copper layer, an insulator like LCP (liquid crystal polymer) or modified polyimides, and a connection layer. The antenna structures are cut to size and exposed with a laser in the production process. But extreme care is necessary because copper and polymers have very different ablation thresholds.

Therefore, if the electromagnetic antenna material is affected negatively by heat, it will shorten its life or cause short circuits. To prevent these risks, Coherent uses a method comprising new picosecond lasers with up to 30 watts that work in the ultraviolet wavelength range of 355 nanometers. This enables scan speeds of several meters per second, typically around ten stages required for the latest antenna designs.

Highly developed USP processing strategy

Coherent has a “Pulse EQ” processing strategy to minimize thermal influences on the sensitive antenna material. The pulse frequency is adapted in real time depending on whether the laser works in a straight line or with narrow curves.

In addition, an integrated active pulse control system ensures stable pulse energies. This results in highly homogeneous sectional images with no thermal effects on the copper-LCP laminate.

Antennas in displays

Similar to integrating keyboards in touch displays, scientists are working on integrating non-visible 5G antennas into displays. In a consortium with industrial partners like SK Telecom and LG Electronics, the team implemented an antenna-on-display (AOD) in the ultra-high resolution touch display of a 28 GHz 5G smartphone for the first time.

By doing this, the scientists conquered the difficulty of integrating three to four modules with dozens of antennas into the installation space of smartphones, which is already very small.

Furthermore, the team achieved the invisibility of the AOD by using nanostructures. Per their paper, with this method, it is possible to integrate antennas in the complete area of OLED or LCDs, even if they are foldable or incorporated into wearables.

Whether the future of 5G lies in direct laser structuring, antenna production with USP lasers, or antenna-on-display technology—one thing is certain: Photonics is sure to play a key role.