RF Filters are an integral part of radio systems, required for keeping the right signals ‘in’ and the wrong signals ‘out’ on both the Transmit and Receive sides of the system.
As mobile wireless technology moves from LTE to 5G, a common question we hear is “How is filtering going to be handled in the unfamiliar territory of millimeter wavelengths?” There is a lot of uncertainty around what filters will be required, where they need to be placed in the base station, how good they need to be, and so forth.
The millimeter wave (mmWave) part of the electromagnetic spectrum is at the high end of the microwave region, which spans ~300 MHz to 300 GHz, and is usually taken to mean frequencies from ~30 GHz to 300 GHz and wavelengths in the range of 1mm to 1cm (Table 1). This dramatically increases available bandwidth, thus expanding achievable data rates, which makes these frequencies extremely interesting to teams around the world working on fifth generation (5G) communications.
One of the questions we get asked regularly is:
‘why not just integrate a filter in the board stack?’
Our answer to this comes in two parts: First there are manufacturing tolerances to consider, and second there is size.
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.
Manufactured using a thin-film process, Microstrip (planar) filters can offer a high quality factor (Q) and a reduced packaging envelope when compared to discrete lumped element designs, and are more practical at higher frequencies. The thin-film design can hold tighter design tolerances due to the distributed transmission lines forming resonant structures. Planar filters are a robust solution, attractive for applications ranging from established platforms, such as military warfare, to emerging technologies, like 5G. Below are some general-purpose resources for additional background, applications, and benefits of Microstrip filters:
In an earlier Blog post we discussed the Shannon-Hartley Theorem in the context of 5G mmWave applications:
Fifth Generation (5G) communication systems are being planned to enable a hundred-fold increase in user data-rates – and with this increase comes a need for significant increases in bandwidth over what is currently available.