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.
Innovating essential high technology systems with demanding specifications is always challenging; making any sort of difference requires extensive resources and deep subject matter knowledge.
But that’s what keeps it interesting.
The advent of fifth generation (5G) communications brings an increased interest in Millimeter Wave (mmWave) technologies. One of the biggest technology challenges engineers face with 5G is how to implement sufficiently high-performance RF filtering in mmWave applications. Given the frequencies involved a distributed element planar approach, such as using Microstrip or Stripline, is often ideal for constructing resonators and filters.
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.
Frequencies in the mmWave spectrum play a key role in 5G communications. RF technology that was developed around existing mmWave applications has evolved to encompass the needs of 5G wireless access. Components for such systems need to be selected for performance and cost – commercial systems are subject to intense price pressure and so both the purchase cost and the implementation cost of a component become important factors in selecting devices for a new design. Another key consideration can be size constraints and the need to preserve valuable board space.
When selecting a filter implementation one factor that is common across all frequencies is optimizing the size of the filter given the application and the required performance.