To help customers with filter selection, we generally provide a lot of information on what our filters can do. But in this new Filter Basics Series, we are taking a step back to cover some background information on how filters do what they do. Regardless of the technology behind the filter, there are several key concepts that all filters share that we will dive into throughout this series. By providing this detailed fundamental filter information, we hope to help you simplify your future filtering decisions. 

In part 3 of this series, we aim to help simplify filter selection by providing an overview and reference point for five of the most commonly discussed filter technology specifications.

At this point, you’ve likely seen a slew of mainstream news articles about 5G causing safety concerns around air travel. In fact, ahead of the rollout of new 5G services from major US telecom companies including Verizon and AT&T on Jan. 19, 2022, many international airlines canceled or delayed flights to major US airports where they believed 5G signals could possibly interfere with the radar signals required to properly operate landing equipment on their planes.

At Knowles Precision Devices, we truly do love all things RF. While we are focused on using our expertise in ceramics and thin film manufacturing to innovate on our high-performance filters, our engineers also enjoy keeping up with the trends impacting the entire RF “ecosystem.” This includes dedicating time to experimenting with various open-source RF modeling and analysis tools that we think our potential non-design engineer customers might find useful. One open-source RF and microwave network analysis tool we have been playing around with lately that we feel does a particularly good job is scikit-rf, which is based on the Python programming language.

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.

This year, Knowles Precision Devices acquired Integrated Microwave Corporation (IMC), a leader in the design and manufacture of custom precision RF microwave filters and multiplexers for the aerospace, defense, and communications industries. This acquisition was particularly exciting as our two companies share deep expertise in engineering high-performance ceramics for RF and microwave applications. And, like Knowles Precision Devices, IMC also has a long heritage of supplying highly reliable components for mission critical space devices that includes applications such as the MARS Orbiters, MARS Landers, and MARS Rovers.

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.

Many critical military operations around the world are increasingly relying on a variety of electronic warfare devices for a range of threat suppression, detection, and neutralization activities. This means that numerous devices operating across the RF spectrum including low-frequency devices in the VHF band and mmWave devices in the Ka band are necessary. As shown in Figure 1, when many electronic warfare devices are in use, a large number of signals are being sent and received and crossing paths. Therefore, it’s easy for any one of these devices to experience issues with interference if proper filtering techniques are not in place.

We are pleased to announce that the Knowles Corporation recently acquired Integrated Microwave Corporation (IMC), a leader in the design and manufacture of custom precision RF microwave filters and multiplexers for the aerospace, defense, and communications industries. With this acquisition, the Knowles Precision Devices Microwave group can now offer a complete range of RF and microwave filtering solutions that support applications from the VHF to the Ka band. In addition to the small, temperature-stable filters our customers have come to know us for, we can now deliver ceramic and cavity filters for lower frequency and/or higher power applications. The full range of the IMC filter technologies we now offer is shown in the graphic below.

Today, electronic warfare applications need to detect a wide variety of signals ranging from UHF communications to GPS and other data signals in the L band to high-frequency radar signals that can fall in the X, S, or K bands. Therefore, these receivers need to operate across an extremely wide range of bandwidths to pick up and understand signals anywhere from 300MHz to 20GHz and beyond. However, a basic general wideband antenna isn’t sufficient for these applications because selectivity is needed to determine what you are actually listening to. Additionally, as if the task of designing an ultra-wideband receiver with selectivity wasn’t challenging enough, RF designers are simultaneously facing pressure to reduce the size, weight, and power (SWaP) of these applications as well.

To provide a better understanding of build-to-print in general and the breadth of our offerings, as well as how our thin-film technology can benefit your applications, we’ve put together a Build-to-Print Basics series. In part 12, we tie everything we’ve discussed so far together and provide more specifics about how we use the processes and options detailed throughout this series to create the custom microwave components you need.