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ELEC 412 - Lecture 14 1
ELEC 412 RF
& Microwave Engineering
Fall 2004
Lecture 14
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ELEC 412 - Lecture 14 2
Lumped Parameter Band-Pass Filter Design
Design an N=3 band-pass maximally flat (Butterworth) filter with a center frequency of 900 MHz. The Bandwidth of the filter is 20% ; That is, BW = (0.20)(900 MHz) = 1.8 MHz or 0.9 MHz.
From the Maximally Flat Low Pass Prototype Table 5-2,
g0 = g4 = 1, g1 = g3 = 1, g2 = 2
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ELEC 412 - Lecture 14 3
Low Pass Prototype Filter
RSg0=1
L1g1=1
C2g1=2
L3g3=1
RLg4=1
Where the normalized center frequency is
c = 1, L = 1.1(2·900 MHz), and
U = 0.9(2·900 MHz)
So that U - L = 1.13Grad/s and Grad/s627.5 ULo
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ELEC 412 - Lecture 14 4
Finding the Filter Components
nH4450 131
LU
gLL
pF713.050
1
1231
gCC
o
LU
nH892.0502
22
gL
o
LU
pF2.3550
1 22
LU
gC
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ELEC 412 - Lecture 14 5
Filter Simulation with Ansoft Designer
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ELEC 412 - Lecture 14 6
Filter Simulation with Ansoft Designer
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ELEC 412 - Lecture 14 7
Some Observations On The Results
• Values of components are unreasonable
• Some other method for implementing the filter design goals must be found
• Solution: Use distributed filters using waveguides
• Richardson Transforms and Kuroda’s Identities
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ELEC 412 - Lecture 14 8
Richards Transformation: Lumped to Distributed Circuit Design
jXL
jBC
L
C
l/ 8 at c
l/ 8 at c
Zo = 1/(j C)
Zo = j L
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ELEC 412 - Lecture 14 9
Kuroda Transforms