‘Constant-k’ implies that the product of underlying impedances Z
1
and Z
2
must be a
constant independent of frequency.
Therefore, L
1
C
1
has to be equal to L
2
C
2
if the filter is to be of a constant-k type. This
constraint is imposed on band-pass filter design.
∴=
=
LCLC
L
C
1122
2
1
by design.
Then, ZZ
This product is define
12
dd as of the filter.
o
o
R
RZZ
L
C
L
C
LCLC
2
12
2
1
1
2
1122
∴====()∵
ZjL
jC
j
LC
C
ZjL
jC
j
L
LC
11
1
2
11
1
22
2
2
2
22
1
1
1
1
=+=−
−
()
==
−
()
ω
ω
ω
ω
ω
ω
ω
ω
//
∴∴=
−
()
×
−
()
=×
−
()
−
ZZ
LC
C
L
LC
L
C
LC
LC
12
2
11
1
2
2
22
2
1
2
11
2
22
1
1
1
1
ω
ω
ω
ω
ω
ω
(()
725
16.14CONSTANT-k BAND-PASS FILTER
16.14 CONSTANT-k BAND-PASS FILTER
Constant-k T-section and Π-section band-pass filters are shown in Fig. 16.14-1.
Step-5 ...
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