RF circuits for applications in the mmWave range (30 to 300 GHz) require high-performance filtering to meet the high-data, high-speed functionality that operating at these higher frequencies promises. However, filters for devices operating in the mmWave range will not function optimally if your printed circuit board (PCB) is not configured appropriately. For this reason, RF design engineers need to make a number of critical PCB design decisions that range from selecting the right materials to developing a board configuration that will limit common issues such as spurious-wave-mode propagation, conductor and radiation losses, unwanted resonance, and dispersion.

Turning 5G wireless communication into a widespread reality will require the use of mmWave frequencies. However, there are many of us RF engineers out there that have spent much of our careers working in the sub-6 GHz range, which actually has quite different needs than mmWave. Therefore, it is critical to get a handle on the key differences between working in this range and mmWave frequencies.

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.

As the RF spectrum becomes more crowded and the number of bandwidth battles grows each year, RF designers are looking for innovative designs that minimize interference while also increasing signal transmission power. Since phased arrays can efficiently maximize gain and signal directivity and minimize interference for both Tx and Rx, adoption of this architecture by RF designers is growing. This means RF designers are also on a quest for phased array filtering options that can help meet the size, weight, and power (SWaP) needs and performance demands required by today’s RF applications. As a result, our engineers have spent a significant amount of time working on an innovative approach that can meet this seemingly impossible combination of requirements.

Spectral efficiency, or bandwidth efficiency, tells us about the channel capacity over a 1Hz bandwidth. It is a measure of the efficiency of a physical layer protocol when it comes to utilizing the spectrum available. To understand how spectral efficiency is calculated, it’s first important to understand the Shannon-Hartley Theorem in the context of 5G mmWave applications (which we discussed in an earlier blog post).

Looking back, 2020 was a year full of big changes regarding how RF spectrum is allocated in the US. Led by the Federal Communications Commission (FCC), multiple portions of the spectrum ranging from the C band to the V band were either opened to new uses and/or auctioned to new users throughout the year. These changes are driving a variety of new opportunities for wireless device manufacturers and broadband and cellular carriers, which is resulting in a range of exciting new challenges for RF technology vendors to help solve. 

When designing an RF or microwave application, you will always need some level of filtering to attenuate or remove unwanted signals from the desired channel. Since the end goal of what a filter must accomplish is quite broad, it may seem daunting to know what qualities to look for in a filter to get there.

At any given time, there are a multitude of signals at a variety of frequencies streaming all around us. Each device that relies on receiving the proper RF signals such as televisions, radios, radars, medical devices, and cell phones, requires some level of filtering. While all filters have the same basic job – remove unwanted or out-of-band signals – the specific job requirements of each filter vary depending on the RF architecture used and the needs of the final device.

Microwave Journal has released an all new mmWave RF Components Guide. This eBook is a collection of seven articles and white papers written to help you make the best component selections when designing your 5G products, several written by engineering experts here at Knowles. Here’s an overview of what’s included in the eBook.

As radio architectures evolve, the need for filters is also evolving. At the same time, the industry is working to miniaturizes mmWave devices while continually minimizing costs. This means RF designers need filter solutions that offer a smaller footprint while keeping prices manageable.