The Knowles Precision Devices DLI brand of technologies are designed to address the complex challenges of implementing high-performance mmWave filters across the widest range of specifications. Our Microwave Product Catalog covers how to select the best catalog or custom components for your application needs, while our new Microwave Products Guide provides valuable information and recommendations for how to work with our DLI brand microwave products once you have the components in hand.

To choose the right filter for your application, you'll need to evaluate filter type, identify the specific filter technology that best suits your application, and ensure the filter meets your required specifications. This post is designed to serve as a quick reference on the common terms that are used to discuss filter type, technology, and specifications.

To start, there are four key Filter behaviors that sort them into types: Low Pass, High Pass, Band Pass, and Band Stop.

As the demand for faster communications across consumer and commercial devices continues to increase, operating frequencies of RF devices are being pushed higher and higher. This creates a number of challenges for RF device designers, as filter size must be reduced to compensate for smaller device sizes and shorter wavelengths while also maintaining high levels of performance. While surface mount technology (SMT), and in particular microstrip implementations, are an excellent option to meet these demands, it is important to note that not every SMT microstrip filter is created equal. There are a variety of choices to discuss with your filter supplier, such as substrate type, plating technology, and topology that can dramatically reduce the size and increase the performance of an SMT microstrip filter. One particular choice that Knowles Precision Devices has guided customers through for decades is the decision to use thin film for these filters.

An Ideal Filter

The Ideal Filter would have unit gain (0dB) in its pass band and a gain of zero (-infinity dB) in its stop band. Between pass band and stop band there would be no indecision and would transition from 0dB to -infinity dB asymptotically. It would pass only the required frequencies without adding or subtracting anything from the signal and like a very discrete and fastidious butler we would not see it - just its perfect management of the frequencies in its care.

When developing mission-critical space applications such as low Earth orbit (LEO) satellites or equipment designed for Mars missions, there are special considerations you must make if you will be operating your RF circuits in a vacuum. This is because when pressure in the vacuum is below 10-2 Torr, a potentially catastrophic phenomenon in RF circuits called multipaction is possible.

X2Y^® technology, which was originally developed by X2Y Attenuators, LLC, is based on a proprietary electrode arrangement embedded in passive components that can be manufactured using a variety of dielectrics. Using this innovative technology, Knowles Precision Devices manufactures high-performance multi-layer ceramic capacitors (MLCCs) that we then use to create a variety of off-the-shelf and custom bypass and noise decoupling capacitors and electromagnetic interference (EMI) filters. Let’s look at how building these components with X2Y is different than using a traditional ceramic MLCC and the resulting benefits.

Since our acquisition of Integrated Microwave Corporation (IMC) in 2020, we have extended our range of RF and microwave filtering solutions to include a wide variety of ceramic coaxial resonators, lumped element filters, and cavity filters from the VHF to the Ka band. During this time, we’ve also continued to innovate on and expand our product offering for one of our most popular filter types – the microstrip filter.  

To help our customers with filter selection, we generally provide a lot of detailed information on what our various filters can do. However, we thought it also might be really helpful for our customers if we took a step back and covered 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. Therefore, we decided it was time to bring together our top engineers so that we could compile their extensive filtering knowledge into a comprehensive Filter Basics ebook. 

As discussed in previous blog posts, resonators are the building blocks used to create filters. Recently, we published a blog post that discussed two different types of resonators – coaxial ceramic and dielectric. In this post, we will cover the details of a third type of resonator – the cavity resonator.

The generation of RF energy is critical for a wide range of technologies including magnetic resonance imaging (MRI), semiconductor manufacturing, industrial lasers, and wireless charging systems that require high-frequency current and minimal instances of power loss. For example, with an industrial laser, the RF plasma excitation, which is when electrons are broken off an atomic bond and plasma forms, requires RF sources ranging from 1kHz to 40.68MHz depending on the energy required, and a CO₂ laser RF power supply that contains a standard source at 13.56MHz, 81MHz, or 125MHz.