Lowpass Filter
-
Upload
nilanshu-manas -
Category
Documents
-
view
58 -
download
0
Transcript of Lowpass Filter
5/12/2018 Lowpass Filter - slidepdf.com
http://slidepdf.com/reader/full/lowpass-filter 1/6
EXAMPLE 1:
Low-Pass Filter Design Using Stubs
Design a low-pass filter for fabrication using microstrip lines.
The specifications are:
• cutoff frequency of 4 Ghz
• third order
• impedance of 50 Ω
• 3 dB equal-ripple characteristic.
• Er = 2.2
• Thickness of dielectric = 62 mill
SolutionStart up the rf & microwave toolbox and select the low pass filter tool.
Then select filter type Chebyshev and g-values as output.Choose the shunt filter configuration.
Fill in the filter specifications and tab the Calculate button.
The normalized low-pass prototype element values are:
Zin = g0 = 1
L1 = g1 = 3.348931C2 = g2 = 0.711668
L3 = g3 = 3.348931Zout = g4 = 1
Figure 1: Low pass filter dialog
5/12/2018 Lowpass Filter - slidepdf.com
http://slidepdf.com/reader/full/lowpass-filter 2/6
The next step is to use Richard's transformation to convert series inductors into series stubs, and
shunt capacitors to shunt stubs. According to this transformation all lengths for the stubs are λ/8.
ZL1 = L1ZC2 = C2
ZL2 = L2
We will use Kuroda's identity nr 2 to convert the series elements into shunt elements.
Select tool Filter Design and the tab button Kuroda's Identities.Fill in the values for Z0 (Zin, Zout) and L (L1,L3)
Now we will use series and shunt equivalent circuit nr 1 to convert the shunt capacitors into shuntstubs.
Figure 2: Low pass prototype filter
L1
C2
L3
1 1
Figure 3: Low pass filter after using Kuroda's Identities
C2
UE
Z0'C3
UE
Z0'C1
1 1
Z0' = 4.3489
C1 = 0.7701
C2 = 0.7116C3 = 0.7701
Figure 4: Series and shunt equivalent circuits dialog
5/12/2018 Lowpass Filter - slidepdf.com
http://slidepdf.com/reader/full/lowpass-filter 3/6
After de-normalization to Z0 = 50 Ω we get the following low pass filter using ideal transmissionlines:
Figure 7: ADS circuit of the low pass filter using ideal transmission lines
Figure 5: Normalized low pass stub filter. All lengths are λ/8.
1
1.2985 1.29851.4053
4.3489 4.3489 1
Figure 6: De-normalized low pass stub filter. All lengths are λ/8.
50Ω
64.9 Ω 64.9 Ω70.3 Ω
217.4 Ω 217.4 Ω50Ω
S_Param
SP1
Step=.05 GHzStop=7.0 GHz
Start=2.0 GHz
S-PARAMETERS
TLIN TL2
F=4 GHz
E=45Z=217.4 Ohm
TLIN
TL3
F=4 GHz
E=45Z=64.9 Ohm
TLIN
TL4
F=4 GHz
E=45Z=70.3 Ohm
TLIN TL1
F=4 GHz
E=45Z=217.4 Ohm
TLIN
TL5
F=4 GHz
E=45Z=64.9 Ohm
Term
Term2
Z=50 Ohm
Num=2
Term
Term1
Z=50 Ohm
Num=1
5/12/2018 Lowpass Filter - slidepdf.com
http://slidepdf.com/reader/full/lowpass-filter 4/6
Figure 8: ADS simulation of the low pass filter using ideal transmission lines
Next step is to convert the ideal transmission lines to microstrip lines.
Select tool Microstrip Calculator and fill in the values for Er (2.2) and substrate height (62 mil).
Fill in a phase 0f 45 deg (λ/8) and F is the cutoff frequency (4Ghz)
Leave all other parameters to default.
Fill in the desired impedance of the transmission lines and synthesize the width an length of the
microstrip lines.
m1freq=dB(S(2,1))=-2.984
4.000GHz
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.52.0 7.0
-50
-40
-30
-20
-10
-60
0
freq, GHz
B
S
2 , 1
m1
m1freq=dB(S(2,1))=-2.984
4.000GHz
5/12/2018 Lowpass Filter - slidepdf.com
http://slidepdf.com/reader/full/lowpass-filter 5/6
W =5.08 mmW = 0.11 mm
L = 2.89 mm
W = 0.11 mm
L = 2.89 mm
W = 3.37 mmL = 2.72 mm
W = 3.37 mmL = 2.72 mm
W = 2.94 mm
L = 2.73 mm
W =5.08 mm
Figure 9: Microstrip linecalculator dialog
5/12/2018 Lowpass Filter - slidepdf.com
http://slidepdf.com/reader/full/lowpass-filter 6/6
Figure 11: ADS simulation of the low pass filter using microstrip lines
m1freq=
dB(S(2,1))=-3.128
4.000GHz
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.52.0 7.0
-50
-40
-30
-20
-10
-60
0
freq, GHz
d B ( S ( 2 , 1
) )
m1
m1freq=
dB(S(2,1))=-3.128
4.000GHz
Figure 10: ADS circuit of the low pass filter using microstrip lines
S_Param
SP1
Step=.05 GHzStop=7.0 GHzStart=2.0 GHz
S-PARAMETERS
VARVAR1
w3=2.76w2=.07w1=3.17l3=6.92l2=7.37l1=6.89
EqnVar
MSUB
MSub1
Rough=0 mm TanD=0 T=35 umHu=1.0e+033 mmCond=1.0E+50Mur=1Er=2.2H=62 mil
MSub
MLIN TL4
L=l3 mmW=w3 mmSubst="MSub1"
MLIN TL7
L=l1 mmW=w1 mmSubst="MSub1"
MLIN TL6
L=l2 mmW=w2 mmSubst="MSub1"
MLIN TL1
L=l2 mmW=w2 mmSubst="MSub1"
MLIN TL3
L=l1 mmW=w1 mmSubst="MSub1"
Term Term2
Z=50 OhmNum=2
Term Term1
Z=50 OhmNum=1