Cavity Filter Series

Overview Performance Specifying Charts Mechanical Outlines

Stopband Rejection and Attenuation

The adjacent curves are used to determine the out-of-band or stopband attenuation for ClearComm's cavity filter line. These curves show the attenuation as multiples of 3 dB bandwidths from center frequency for filters up to 7 sections. For requirements with greater rejections needed, please contact the factory.

The formula for approximate stopband attenuation:

3 dB Bandwidths from f0 =
Reject Frequency - Center Frequency
       3 dB Bandwidth

 

Example:
Center Frequency (f0) = 1000 MHz
3 dB Bandwidth = 10 MHz
60 dB attenuation required at 980 and 1030 MHz

We must first calculate the number of 3 dB Bandwidths away from Center Frequency

    1000 – 980    =2       1030 – 1000    =3
10 10

We can see from the table above that to achieve 60 dB attenuation at 2 3dB bandwidths away that we need a minimum of 5 sections and that at 3 3dB bandwidths away we need a minimum of 4 sections. Always use the higher number of sections.


Insertion Loss

Knowing the number of sections, center frequency and bandwidth of the filter and the 'Q' factor found from the charts below, the insertion loss may be calculated from the formula:

Loss =   N + 1.5    + 0.2
'Q' x %BW