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.
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.
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.
In an earlier Blog post we discussed the Shannon-Hartley Theorem in the context of 5G mmWave applications:
Fifth Generation (5G) communication systems are being planned to 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.
This document is designed to act as a quick reference on some terms that are used to discuss filter technology.
There are four key Filter behaviors that sort them into types: Low Pass, High Pass, Band Pass and Band Stop.