With the promised delivery date of 5G wireless communication fast approaching, the world is waiting to see if this next-generation network will hit its ambitious goals of 10 Gbps peak data rates, less than 1 ms latency, 10 times greater energy efficiency, and more. In past decades, each generation of mobile systems – from 1G analog systems to 2G digital standards to 3G mobile broadband capabilities to 4G LTE and LTE-Advanced networks – has overcome a unique set of challenges. Leaps in technology are necessary to enable these advancements in performance.
In order to tackle the first challenge of increased data rates, we can return to the Shannon-Hartley Theorem that explains the maximum amount of error-free digital data that can be transmitted over a channel of a given bandwidth in the presence of noise:
where C is channel capacity, M is the number of channels (e.g., the MIMO order), B is the bandwidth, and S/N is the signal-to-noise ratio. In order to increase channel capacity (or data rates), one of the primary factors of focus for 5G is bandwidth, as well as how much bandwidth is available in a given part of the spectrum.
Nowadays contiguous bandwidth of 100 MHz is hard to find in the LTE spectrum landscape. Given that the 5G peak data rate goal is 10 Gbps, the increase in channel capacity must come from somewhere. A key innovation at the heart of 5G is utilizing new spectrums where increases in bandwidth are easier to obtain. Therefore, the millimeter wave (mmWave) spectrum – which technically corresponds to Extremely High Frequencies (EHFs) from 30 GHz to 300 GHz but generally also includes 20 GHz and higher centimeter-scale wavelengths – is of great interest to designers because it offers the most dramatic increase in available bandwidths compared to available spectra below 3 GHz.
As we enter the unfamiliar territory of the mmWave spectrum, one of the main questions that arises is filtering. In the LTE generation, developers are very familiar with the available filtering technologies that work, namely surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters. These acoustic filters cover a range of frequencies up to 6 GHz, come in small sizes, and offer a good performance-to-cost tradeoff that makes them the dominant off-chip approach in mobile devices today.
Unfortunately, analogous filtering options for the mmWave spectrum seem to have major issues in viability, performance, size, availability, and so forth. Even the research teams helping to write the 5G standards have yet to provide information on what filters will be required, where they need to be placed in the base station, and what performance metrics they need to meet. Based on our years of experience working with the mmWave spectrum, Knowles Precision Devices wrote an in-depth technical article for Microwave Journal that discusses key specifications for mmWave filtering and practical options available for consideration. Click the button below to read the full paper:
