RF Filters and Types

An RF (radio frequency) filter is an electronic component used to allow signals to pass through at certain frequencies but reject signals at any frequency outside the approved range. RF filters are commonly used as a base for duplexers and diplexers to combine or separate frequency bands. One problem that can occur when sending and receiving signals is load impedance on the circuits. The load impedance should match the internal impedance of the lowpass and highpass filters. This minimizes the amount of signal reflections when many frequency signals are being sent out or received. This blog will explain the types of RF filters and their characteristics.

The first type of RF filters are known as bandpass filters. These are offered in a variety of ranges from very narrow band to medium and broadband with low loss. High power applications of bandpass filters have a wide array of topologies including cavity, combline, interdigital, coaxial, suspended substrate stripline, waveguide, and mixed topologies. Bandpass RF filters feature a design coupled to the system between two ports. It is designed to select a particular frequency band that will be able to pass through, while all others are rejected.

The second type of RF filters are lowpass filters. These are low loss broadband filters that provide high power applications from a wide range of topologies such as lumped element, coaxial, and suspended substrate stripline, in addition to others. Lowpass filters receive lower frequencies and will reject higher gigahertz frequencies that exceed a determined decibel cut off level. Lowpass filters have direct access to the port. Any frequency below the cutoff level will be directed to the second port. Lowpass filters function by triggering insertion loss.

The third type of RF filters, highpass filters, are broadband filters with low loss offered in high power applications. The topologies of highpass filters include lumped element, suspended stripline, and multiple topologies. These work in the opposite way of lowpass filters. Frequencies above the set decibel cutoff level will be allowed to pass through the filter on its way to the third port. Low frequencies are entirely rejected.

The final type of RF filter is known as notch or bandstop filters. These are offered with a very narrow band high rejection to medium and broad band filters. These offer low loss for high power applications from a broad scope of topologies such as cavity, combline, interdigital, coaxial, suspended, substrate stripline, waveguide, and others. There are also diplexer and multiplexer filters, which are a combination of bandpass, lowpass, and highpass filters. Whatever filter best suits your needs, you can find it at Plane Parts 360.



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March 18, 2021

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