The RF filter is one of the essential key components in the radio frequency system. It is mainly used for frequency selection—letting the required frequency signal pass and reflecting the unwanted interference frequency signal.
A classic example of a filter application is a receiver or transmitter front end, as shown in
Figure 1: Receiver RF Front-End
As can be seen from Figure 1, the filter is widely used in the RF band, IF band and Baseband of the receiver. Although the digital technology develops rapidly, the digital filter has replaced the analog filter at the baseband part and even the IF band section, but the filter of the RF part is still irreplaceable. Therefore, the filter is one of the essential key components in the radio frequency system.
Figure 2: Super-heterodyne receiver
Figure 3：The Composition of a GPS receiver
RF Filter Types
By frequency: low-pass, high-pass, band-pass, band-stop filters, etc.;
By structure: LC filter, Surface Acoustic Wave/Body Acoustic Wave Filter, Spiral/Helical Filter, Dielectric Filter, Cavity filter, High Temperature Superconducting Filter, and Planar Structure Filter.
By frequency response functions, it can be divided into: Chebyshev, Generalized Chebyshev, Butterworth, Gaussian, Bessel function, Elliptic function, etc.
How to choose a RF Filter?
When selecting a filter, the first thing to determine is whether to use a low-pass, high-pass, band-pass or band-stop filter.
The following is to introduce the types by frequency response characteristics and functions, such as high-pass, low-pass, band-pass and band-stop classified.
Butterworth VS Chebyshev Low Pass Filter
Butterworth VS Chebyshev Band Pass Filter
Butterworth VS Chebyshev Band Stop Filter
Low pass and band pass filters are the most commonly used filters.
Low-pass Filter is widely used in the image suppression of the mixer part and the harmonic suppression of the frequency source part.
Band-pass Filter is widely used in receiver front-end for signal selection, or after the transmitter power amplifier for spurious suppression, or at frequency source section for spurious suppression, etc.
In the next article, we will further introduce the electrical characteristic indicators that define the filter performance, so stay tuned.