Microwave filtering
Passive microwave circuits - Filters and cavities

An ideal filter device is one that achieves perfect transmission for all frequencies within the passband and infinite attenuation in the cut-off bands. Such ideal characteristics cannot be achieved in practice, and the aim of a filter designer is to approach these ideal constraints as closely as possible, while accepting a certain tolerance.

The working frequencies of the filters currently in production are extremely wide. .

Filters can be divided into three categories:

• low-pass filters which transmit all signals with frequencies between zero and a certain limit frequency f_c, with frequencies above f_c being attenuated;

• high-pass filters which pass all frequencies above a frequency f_c and attenuate all frequencies below ;

• bandpass filters for which only frequencies within the interval [f₁...