The 5G “LIVER”

We all know that in every healthy, functioning human body, there are many organs working in perfect synergy, each performing different roles in keeping the body healthy and functioning. Similarly, in every kind of system, whether its a mechanical system, electrical system or a telecommunication system, there are many “organs” that perform specific roles. So, today we are gonna talk about the 5G “liver”. What is this “liver”? It is the microwave filters.

Microwave “Liver” Filter

The keyword “Liver” naturally explains its function well which is to filter “toxic” in a system in such a way that useful ingredients can be processed or extracted. So why are microwave filters considered as “liver”? This is because microwave filter remove all the signal interference propagating in free space, be it frequency spectrum generated or degenerated by other applications or varying power level, microwave filters remove them to allow a clean signal to pass through. Ever wonder why you can hear someone clearly on a phone? That’s all thanks to good microwave filter system which allow retrieval of meaningful information in the desired filtered signal. In fact, this “liver” is so hidden yet important that it is found in all generations wireless mobile communication system. From 1G to 5G, all of them requires microwave filters to function properly.

Here’s another interesting fact on why microwave filters are liken to the liver. It is common that antenna is the most visible-to-consumer devices installed at every mobile base station with significantly large dimension in appearance. One may not know that the microwave filter for mobile base station is also one of the biggest component in the system. It size can be equal or bigger than antenna depending on certain application or requirements. The “Liver” is also one of the biggest organ in the human body and hence the best analogy for representing the microwave filter in the 5G system.

Mobile Base Station Diplexer (FILPAL)

Microwave Filters in Base Stations

You may wonder where is this filter situated in the base station? The conventional base station for 3G or 4G separates the antenna and filter unit where the latter is sitting in landed containers that are not visible to consumers. However, the scenario changes when coming to 5G implementation where antenna and filter will be attached and installed as a singular outdoor unit. Here comes the challenge. It is expected that the 5G base station that will be either sub-6GHz or mm-wave would have smaller form factor, one is due to the change of frequency of operation and the other requirement being cost and size. The size of the antenna and filter will directly impact the quality of the base station. Hence maintaining the same quality and performance while maintaining smaller size base station poses a design challenge to researchers, engineers and scientists.

Designing the 5G “Liver”

Air Cavity Filter

Lets discuss about some of the details about filter miniaturization techniques which will possibly be implemented in 5G base station. Conventional filters utilize air cavity resonator to achieve high Q factor with low loss at the passband and high rejection at the stopband. The importance of the low loss performance at the passband is extremely important as it determines the relaxation of power amplifier specification. In other words, lossy passband will stress the driving power of the power amplifier in order to maintain good quality signal resulting in high power consumption and high cost with low battery life.

Typical measured response of BTS filter

The rejection specification is also equally important to perform the function of a healthy “liver”. However, air cavity filter has the disadvantage of being relatively big in size. Dielectric resonator has become popular in which the achievable Q-factor (quality) can be much higher with smaller size resonator due to the relative permittivity being greater than 1. This is further stressed for the realization of multi-mode resonator in order to reduce the size of the filter.  

The discussion of multi-mode resonators will be the topic for another day. For now, readers may refer to the figures below for some examples of base station filter. One may notice that the picture shown is entirely different from the electronic filter learnt in the school and yet the principles still applied.

Here at FILPAL, we are passionate to share and discuss on technologies related with telecommunication. Subscribe to our blog or leave us a comment if you find this article interesting. We look forward to share more information with you all in our future articles.

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