Why are RF filters becoming increasingly important?
2019-07-22
RF filter
Why is it becoming increasingly important?
The rapid growth of mobile wireless data and 4G LTE networks has led to a growing demand for new bands and combinations of bands through Carrier aggregation to accommodate wireless traffic. The 3G network only uses about five frequency bands, while the LTE network currently uses over 40 frequency bands. With the arrival of 5G, the number of frequency bands will further increase.
Interconnected devices must transmit cellular, Wi Fi, Bluetooth, and GPS signals across multiple frequency bands, while also avoiding interference. We may immediately think of smartphones, but this is true for shark fins, cellular base stations, radar and communication systems installed on the roof, as well as industrial, scientific, or medical applications connected to the Internet of Things (IoT). At this point, filters are needed.
A smartphone without a filter is just a brick
Like antennas, filters are becoming an increasingly important part of networked mixers. The device will receive various frequencies, and the filter can allow the desired frequency to pass while suppressing unwanted frequencies. In other words, filters are like Gandalf in John Ronald Riel Tolkien's book "The Lord of the Rings": "You can't pass through here!" Today's devices are usually equipped with 30 to 40 filters to avoid interference. As the next generation of high-end smartphones requires more filters, this situation will become even more complex.
Filter design Challenges
Filters are essential tools for RF design engineers, but they also face many challenges. For starters, the performance of filters varies with temperature. Nowadays, filters in various devices can withstand an average temperature of 60 degrees Celsius (140 degrees Fahrenheit) or higher, while indoor filters can withstand an average temperature of 25 degrees Celsius (77 degrees Fahrenheit), and filters embedded in shark fins or rooftops can withstand even higher temperatures. The higher the temperature of the filter, the harder it is to filter out a specific frequency, and thus the more likely the signal is to "drift" to adjacent frequency bands.
Due to the close proximity of many newly allocated frequency bands to existing ones, managing temperature drift becomes particularly important. At the same time, Carrier aggregation (CA) is also developing rapidly. Cellular service providers can combine up to five carrier channels to improve network performance, of which accurate filtering is a prerequisite.
To address temperature issues, the RF industry is developing low drift and drift free filter technologies. Surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters can still maintain a highly stable performance when the temperature changes, which can meet the stringent performance requirements of emerging equipment.
As mentioned earlier, the next generation of high-end smartphones also needs to be equipped with more filters. Similar to all other components of RF, the space left for the filter is very limited. Engineers must be able to integrate multiple filters into smaller spaces in order to achieve higher performance.
Duplexers, triplers, quadruplers, and even hexamers are collectively referred to as multiplexers. Multiplexers can integrate multiple filters into one device, helping designers save space, simplify design, meet performance requirements, and avoid interference.
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