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. At mmWave frequencies this can be prove to be a particularly interesting problem, given the change in the physical dimensions of the system as one moves from say 600MHz to 38GHz.
The quality factor (Q) of a resonator is expressed as the ratio of stored versus lost energy per oscillation cycle. Overall losses through a resonator increase as Q factor drops and will increase more rapidly with frequency for lower values of resonator Q. However, truly understanding how Q factor is determined is a bit more intricate. Let’s take a closer look.
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.
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.