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.

As early adopters of beamforming technology in the 1960s, aerospace and defense organizations have a lot of experience using the initial large-scale active electronically scanned arrays (AESAs) for military radar tracking applications. But these arrays aren’t as convenient for some applications today as the operational frequencies of the targets of interest for many military applications are increasing. This means the wavelengths of the signals that need to be monitored are getting shorter and these radar applications need denser arrays since antenna spacing needs to be set at one half the wavelength. For example, at 25GHz, the wavelength in free space is approximately 12mm (0.47”), leading to half-wave spacing for antennas of 6mm (0.24”). Also, as arrays become denser, the new challenge for RF system designers is avoiding interference in these tighter spaces, especially when transmitting signals.

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. 

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 and components for such systems need to be selected for performance and cost. Commercial systems are subject to intense price pressure, making both the purchase cost and the implementation cost of a component important factors in selecting devices for a new design. Another key consideration is likely size constraints and the need to preserve valuable board space.

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.

Planning is in the works for Fifth Generation (5G) communication systems that will 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. Why does bandwidth follow when we ask for an increase in data rates? 

Many microwave applications, such as repeaters, and electronic warfare equipment, require increased spectral resolution. This means these devices only need to look at a narrow slice of a given band. Filters that are optimized for the whole band, such us our planar microstrip devices, are too broadband for these applications. Likewise, traditional high Q filters, such as waveguide devices, are often too large to consider using in these types of applications.

With more than 2,000 satellites currently orbiting the Earth, and that number expected to quintuple in the next 10 years, the demand for space-ready components is exponentially increasing (Figure 1). At the same time, the technology needed to control and transmit satellite data has changed from mechanically controlled parabolic or dish technology to active electronically steered arrays (AESAs).