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g86
Joined: 21 Jan 2003
Posts: 208
Helped: 4
Location: On top of antenna :))
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 08 Mar 2003 14:39 Best Chamfer for microstrip discontinuities |
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How to get best chamfering in microstrip lines (in terms of chamfering factor or angle) for:
1. 45, 90 and 135 degree bends
2. single step and double step
3. T-junctions
What are the merits and de-merits of these methods?
How to calculate the exact path length in such chamfers?
  
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flatulent
Joined: 19 Jul 2002
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Location: Middle Earth
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| 08 Mar 2003 17:15 it all depends |
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It falls in two categories.
1. Routing requirement. The line is restricted on where it can run and it has to turn a corner to get to the destination. 90 degree bends with the outer corner cut off can totally eliminate reflections. The 135 degree bend comes from digital design where the layout programs do not cut the corners of bends off. This 135 bend has a low enough reflection for digital signals that it is acceptable. The 45 internal angle bend is totally unacceptable and should be avoided.
2. Electrical requirements. The step in impedance is intentional for filtering purposes or impedance transforming purposes. The step can be modeled as a shunt reactance. Your simulator program will take this into account. T junctions also fall into the intentional discontinuity area. Adding extra triangles of metal will only make things worse because it add extra unknowns to your design.
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g86
Joined: 21 Jan 2003
Posts: 208
Helped: 4
Location: On top of antenna :))
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| 08 Mar 2003 19:01 Re: it all depends |
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Oops, I am expecting exact numerical values  . These theoretical basics I know:)
| flatulent wrote: |
It falls in two categories.
1. Routing requirement. The line is restricted on where it can run and it has to turn a corner to get to the destination. 90 degree bends with the outer corner cut off can totally eliminate reflections. The 135 degree bend comes from digital design where the layout programs do not cut the corners of bends off. This 135 bend has a low enough reflection for digital signals that it is acceptable. The 45 internal angle bend is totally unacceptable and should be avoided.
2. Electrical requirements. The step in impedance is intentional for filtering purposes or impedance transforming purposes. The step can be modeled as a shunt reactance. Your simulator program will take this into account. T junctions also fall into the intentional discontinuity area. Adding extra triangles of metal will only make things worse because it add extra unknowns to your design. |
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g86
Joined: 21 Jan 2003
Posts: 208
Helped: 4
Location: On top of antenna :))
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| 09 Mar 2003 14:19 |
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Yesterday I was trying to optimize 90 degree chamfer and found 0.55 chamfering is much better than 0.5. I have used IE3D as simulator.
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flatulent
Joined: 19 Jul 2002
Posts: 4856
Helped: 292
Location: Middle Earth
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| 09 Mar 2003 17:12 sources of error |
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| Be careful with the results of simulators. There are many variables that come into play such as the thickness of the metal and the angle of the edges. There is also the operating frequency. Simulators are not accurate enough to take these items into effect. I have seen many comparisons of simulator results vs measurements for patch antennas. They were always off by a few percent in frequency and a few dB in magnitude.
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g86
Joined: 21 Jan 2003
Posts: 208
Helped: 4
Location: On top of antenna :))
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| 10 Mar 2003 12:20 Re: sources of error |
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Why? I have taken care of all the parameters requred and the value nou I obtained in 0.56 which is very closer to that suggested by KC Gupta or T Edwards.
| flatulent wrote: |
| Be careful with the results of simulators. There are many variables that come into play such as the thickness of the metal and the angle of the edges. There is also the operating frequency. Simulators are not accurate enough to take these items into effect. I have seen many comparisons of simulator results vs measurements for patch antennas. They were always off by a few percent in frequency and a few dB in magnitude. |
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mwpro
Joined: 20 Apr 2001
Posts: 83
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| 10 Mar 2003 15:22 |
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Curious to know how much is much better? My experience is that they doesn't differ by much.
mwpro
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g86
Joined: 21 Jan 2003
Posts: 208
Helped: 4
Location: On top of antenna :))
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| 10 Mar 2003 19:16 Re: sources of error |
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You are correct today I chacked with some more materials as your suggestion and found the factor depends upon the material too. Now it is too complecated. Means I could not end up with a solid answer. And for some cases 0.5 is "BEST Choice" for 90 degree which includes air. But I could not get the answer of exact path length. That also varies...nothing is stable.
Later I will try with other chamfers. Thanks all of you.
| flatulent wrote: |
| Be careful with the results of simulators. There are many variables that come into play such as the thickness of the metal and the angle of the edges. There is also the operating frequency. Simulators are not accurate enough to take these items into effect. I have seen many comparisons of simulator results vs measurements for patch antennas. They were always off by a few percent in frequency and a few dB in magnitude. |
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