by Fandy Wei, Senior Director, OEM Marketing in Asia, Isola Asia Pacific (Taiwan) Inc.
It seems like only yesterday, but Fifth Generation (5G) cellular networks have been making wireless connections for almost four years. Already, some of the major carriers and test-equipment developers are looking ahead to around 2029 or 2030 and the expected start of Sixth Generation (6G) networks. Still, 5G has room for expansion, especially at higher frequencies, and it may be in the design and development of that “upper-frequency half” of 5G networks that much can be learned to prepare for 6G.
The part of the 5G New Radio (NR) standard developed by the international Third Generation Partnership Program (3GPP) technical standards committee that is so familiar to most 5G users refers to frequency range FR1 from 410 to 7125 MHz and its use of those terrestrial frequency bands has proven efficient and effective. But the many futuristic features that will set 5G apart from 4G, including blazing data rates and video streaming without delays, will be provided by 5G’s higher FR2 frequency range from 24.25 to 71.00 GHz typically using smaller cells placed closely together to overcome the propagation limits of higher-frequency signals.
The large 5G FR2 bandwidth available at millimeter-wave frequencies is expected to be exhausted before 6G is commercially available, with users finding many new applications for 5G networks in the forms of Internet of Things (IoT) sensors, control of unmanned vehicles, even connectivity to “self-driving” autonomous vehicles, with mobile video conferencing becoming a standard practice as businesses continue to abandon traditional “fixed” workplaces. To exceed the performance levels established by 5G networks, telecom providers are estimating 6G data rates many times that of 5G, as fast as 95 Gb/s. Such high-speed data rates require large channel bandwidths, which are available at higher frequencies. Those higher frequencies with their wider bandwidths will enable applications as of yet unavailable, such as streaming of real-time data and imaging with less than 1 μs latency for medical procedures and operations where a patient is remote from a surgeon, or the use of virtual reality (VR) and augmented reality (AR) to enable three-dimensional meetings and conferences in which no one is present.
Some 6G prognosticators are pointing to frequency spectrum to the upper limits of the millimeter-wave range, from 30 to 300 GHz, or even to the Terahertz range of 0.3 to 3 THz (300 to 3000 GHz). Circuit materials capable of supporting millimeter-wave circuits are currently available, for essential 5G components such as array antennas and filters. But the THz frequency range is still largely the realm of medical imaging and other scientific researchers. Significant advances in conductive and dielectric materials will be needed to support the micrometer-dimensioned transmission lines needed for THz circuits. The opportunity to learn more about those 6G circuit requirements is right now, with the FR2 buildup of 5G network infrastructure.
By understanding how circuit materials respond to the needs of millimeter-wave circuit design, those lessons can guide the development of circuit materials with the characteristics needed for 6G systems. Circuit materials such as I-Tera®MT40, Astra® MT77, and Tachyon® 100G from Isola Group exhibit the traits needed for 5G’s FR2 region and even beyond 100 GHz, with minimal loss and excellent dimensional stability.
These reliable circuit materials maintain high dimensional stability with temperature, minimizing the ill-effects of temperature during normal operation and during manufacturing processes, such as soldering. All three circuit materials are noteworthy for their good high-temperature durability, characterized by a glass transition temperature (Tg) of +200°C. The materials absorb very little moisture and so will suffer only minimal degradation in performance even under high-humidity operating conditions.
These three high-performance circuit materials are examples of the materials being used to assemble printed-circuit boards (PCBs) for the FR2 millimeter-wave frequency range of 5G networks. At those frequencies, the low loss and minimal distortion afforded to those circuits is making possible wireless communications within a part of the frequency spectrum once thought impractical for commercial use. Those same three circuit materials also provide realistic foundations for high-speed-digital (HSD) circuits, since the electronic modules within 5G small cells often involve mixed-signal combinations of high-frequency analog circuits and HSD circuits.
Exploring how these circuit materials will respond to the needs of 5G networks operating within their FR2 frequency bands will provide useful lessons for the even higher frequencies and performance goals of 6G networks when they come. It may seem like only yesterday, but technical advances have ways of creeping up quickly.
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