The curves shown indicate the stopband frequencies normalized to the 3
dB cutoff for filters of 2 to 12 sections. A ratio of stopband frequency
to 3 dB bandwidth is used.
The curve shown indicates the frequency response resulting from the circuit used.
A LC-Series filter has a cutoff frequency of 650 MHz. A stopband attenuation
of 30 dB is required at 900 MHz.
Calculate the number
of sections as follows:
Number of 3 dB bandwidths
from cutoff frequency = The curve indicates that a minimum of 4 sections
Insertion Loss Calculation
Knowing the number of sections, and cutoff frequency of the filter, insertion loss may be calculated from the following formula:
Loss = N x 0.2
1. Number of sections = 4
2. IL = 4 x 0.2 = 0.8 dB
Note: For Lowpass filters, insertion loss is calculated at 0.9 times the cutoff frequency