Elliptic / Cauer Filter

- basics of the Elliptic or Cauer Filter - its performance, key facts and how it can be used in RF filter applications.

The elliptic filter of Cauer filter is a form of RF filter that provides a very fast transition from pass-band to the ultimate roll off rate.

The Cauer or elliptic filter is characterised by the fact that it has both pass-band and stop-band ripple.

Despite the ripple, the elliptic filter offers very high levels of rejection and as a result it is used in many RF filter applications where rejection levels are key.


Cauer filter naming

The elliptic filter is also often referred to as the Cauer filter. It takes its name from Wilhelm Cauer.

Cauer was born in Berlin, Germany in 1900. He trained as a mathematician and then went on to provide a solid mathematical foundation for the analysis and synthesis of filters. This was a major step forwards because prior to this the performance and operation of filters was not well understood.

Cauer provided the solid mathematical approach required to enable filters to be designed to meet a requirement rather than the approximate methods that had previously been used.

Graduating from the Technical University of Berlin in 1924, Cauer worked as a lecturer at Institute of Mathematics at the University of Gottingen. However as a result of the depression he moved to the USA, studying at MIT and Harvard, but later returned to Germany.

Sadly Cauer was in Berlin at the end of the Second World War and his body was found in a mass grave in Berlin.


Elliptic Cauer filter basics

The elliptic filter is characterised by the ripple in both pass-band and stop-band as well as the fastest transition between pass-band and ultimate roll-off of any RF filter type.

The levels of ripple in the pas-band and stop-band are independently adjustable during the design. As the ripple in the stop-band approaches zero, the filter becomes a Chebyshev type I filter, and as the ripple in the stop-band approaches zero, it becomes a Chebyshev type II filter.

If the ripple in both stop-band and pass-band become zero, then the filter transforms into a Butterworth filter.

There are two circuit configurations used for the low pass filter versions of the Cauer elliptic filter. One has the parallel capacitor and inductor in the signal line as shown below:

Elliptic Cauer Filter Circuit

The other version of the Elliptic filter of Cauer filter has a series inductor and capacitor between the two signal lines as below:

Elliptic Cauer Filter Circuit

By Ian Poole


. . . .   |   Next >>



Read more popular RF filter tutorials . . . . .

Filter basics Filter design HPF design  
Simple LPF Simple HPF Simple BPF  
Butterworth Chebyshev Bessel Elliptic / Cauer

Share this page


Want more like this? Register for our newsletter





Too good to be true - the cost of counterfeit electronics and how to avoid them Miguel Fernandez | Avnet EMEA
Too good to be true - the cost of counterfeit electronics and how to avoid them
The issue of counterfeit electronic components is one that has troubles the electronics industry - using them can have some major issues, everything from being removed from a preferred suppliers list to a reduction in quality.
Whitepapers
Cost-Efficient & Extensible RF Spectrum Monitoring & Management
Discover how to use high-performance portable analyzers, open software and PC integration for field analysis, remote deployments, and efficient and effective spectrum management.

More whitepapers










Radio-Electronics.com is operated and owned by Adrio Communications Ltd and edited by Ian Poole. All information is © Adrio Communications Ltd and may not be copied except for individual personal use. This includes copying material in whatever form into website pages. While every effort is made to ensure the accuracy of the information on Radio-Electronics.com, no liability is accepted for any consequences of using it. This site uses cookies. By using this site, these terms including the use of cookies are accepted. More explanation can be found in our Privacy Policy