
650 Network Analysis and Synthesis
The resonant frequency of the shunt arm is so chosen such that it is slightly higher than that of
the constant K-type filter.
That is,
∞
resonant frequency
c
At the frequency f
∞
, the impedance of shunt branch is zero, that is, the attenuation is infinite.
This can be seen from the expression for attenuation as
=
−
2
4
1
1
2
cosh
Z
Z
At f = f
∞
, Z
2
= 0 and hence
. This produces very sharp cut-off or attenuation.
Here, m is a constant and
.
13.9.1 m-Derived T-section
As mentioned earlier, m-derived T-section as shown in Figure 13.50
can be obtained from constant K-type filter shown in Figure 13.49
by making the follo ...