Stopband Rejection and Attenuation

The adjacent curves are used to determine the out-of-band or stopband attenuation for ClearComm's Discrete Element Highpass Filters. These curves show the attenuation as multiples of the normalized stopband frequency to the 3 dB cutoff frequency for filters up to 12 sections. For requirements with greater rejections needed, please contact the factory.

The formula for approximate stopband attenuation:

3 dB Bandwidths from Cutoff Frequency = Reject Frequency / Cutoff Frequency

Example:
Cutoff Frequency (fc) = 1215 MHz
35 dB attenuation required at 900 MHz

We must first calculate the ration of the two frequencies:

900 / 1215 = 0.74

We can see from the table above that to achieve 35 dB attenuation at .74 away that we need a minimum of 5 sections. Always use the higher number of sections.

Insertion Loss

Knowing the number of sections, the insertion loss may be calculated from the formula:

Loss = 0.2 x N

Example:
Number of sections = 7
Insertion Loss = 7 x 0.2 = 1.4 dB

Note: For Highpass filters, insertion loss is calculated at 1.1 times the cutoff frequency