Difference between revisions of "RF Tutorial Lesson 5: Designing Lumped and Distributed Microstrip Lowpass Filters"
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|All versions|{{download|http://www.emagtech.com/downloads/ProjectRepo/RFLesson5.zip RF Lesson 5}} }} | |All versions|{{download|http://www.emagtech.com/downloads/ProjectRepo/RFLesson5.zip RF Lesson 5}} }} | ||
− | + | == What You Will Learn == | |
In this tutorial you will build and analyze a stepped-impedance microstrip lowpass filter based on a standard lumped LC filter design. | In this tutorial you will build and analyze a stepped-impedance microstrip lowpass filter based on a standard lumped LC filter design. | ||
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− | [[File:RF52.png|thumb| | + | [[File:RF52.png|thumb|left|640px|A lumped LC lowpass filter.]] |
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− | [[File:RF53.png|thumb|720px|Graph of S11 and S21 parameters of the ladder LC filter over the frequency range 500MHz-3GHz.]] | + | [[File:RF53.png|thumb|left|720px|Graph of S11 and S21 parameters of the ladder LC filter over the frequency range 500MHz-3GHz.]] |
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== Designing a Stepped Impedance Microstrip Lowpass Filter == | == Designing a Stepped Impedance Microstrip Lowpass Filter == | ||
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A distributed microstrip version of the above ladder LC filter can be realized using consecutive low- and high-impedance line segments. It is well known that short segments of low- and high-impedance transmission lines behave like capacitive and inductive elements, respectively. Therefore, you will need four low-Z0 microstrip segments to replace the capacitors C1, C2, C3 and C4, and three high-Z0 microstrip segments to replace the inductors L1, L2 and L3. The transformations are based on the following equations: | A distributed microstrip version of the above ladder LC filter can be realized using consecutive low- and high-impedance line segments. It is well known that short segments of low- and high-impedance transmission lines behave like capacitive and inductive elements, respectively. Therefore, you will need four low-Z0 microstrip segments to replace the capacitors C1, C2, C3 and C4, and three high-Z0 microstrip segments to replace the inductors L1, L2 and L3. The transformations are based on the following equations: | ||
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for capacitors. Here Z<sub>high</sub> and Z<sub>low</sub> are the high and low characteristic impedances of the narrow and wide microstrip segments, respectively, and R<sub>0</sub> is the reference impedance of the filter. | for capacitors. Here Z<sub>high</sub> and Z<sub>low</sub> are the high and low characteristic impedances of the narrow and wide microstrip segments, respectively, and R<sub>0</sub> is the reference impedance of the filter. | ||
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+ | <table> | ||
+ | <tr> | ||
+ | <td> | ||
+ | [[File:RF58.png|thumb|left|640px|The top view of layout of the Stepped Impedance Mirostrip Lowpass filter.]] | ||
+ | </td> | ||
+ | </tr> | ||
+ | </table> | ||
For this project, you will use 0.5mm-wide and 5mm-wide microstrip lines to realize Z<sub>high</sub> and Z<sub>low</sub>, respectively. As you found earlier, these lines provide approximately 102Ω and 30Ω impedances, respectively. Using the above transformations, the following table for the segment lengths is obtained: | For this project, you will use 0.5mm-wide and 5mm-wide microstrip lines to realize Z<sub>high</sub> and Z<sub>low</sub>, respectively. As you found earlier, these lines provide approximately 102Ω and 30Ω impedances, respectively. Using the above transformations, the following table for the segment lengths is obtained: | ||
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− | [[File:RF54.png|thumb| | + | [[File:RF54.png|thumb|left|640px|The schematic of a Stepped Impedance Microstrip Lowpass filter.]] |
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− | [[File:RF56.png|thumb| | + | [[File:RF56.png|thumb|left|720px|The Stepped Impedance Mirostrip Lowpass filter including step discontinuity models.]] |
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− | [[File:RF57.png|thumb| | + | [[File:RF57.png|thumb|left|720px|Graph of S11 and S21 parameters of the stepped-impedance microstrip filter including step discontinuity models over the frequency range 500MHz-3GHz.]] |
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Latest revision as of 23:34, 8 November 2016
Contents
What You Will Learn
In this tutorial you will build and analyze a stepped-impedance microstrip lowpass filter based on a standard lumped LC filter design.
Analyzing a Lumped Ladder LC Lowpass Filter
The following is a list of capacitors and inductors needed for this part of the tutorial lesson:
Part | Value |
---|---|
C1 | 0.71pF |
L1 | 4.96nH |
C2 | 2.87pF |
L2 | 7.96nH |
C3 | 2.87pF |
L3 | 4.96nH |
C4 | 0.71pF |
This is a classic Butterwoth LC lowpass filter with N = 7. The cutoff frequency of this filter is 2GHz and it attenuates to more than -20dB at 3GHz. Place the parts and connect them as a ladder filter. Mark the input and output of your lumped LC filter with two Net Markers: IN and OUT.
Run a network analysis of this two-port circuit according to the table below: