Lumped elements dimensions and placement considerations

How to use openEMS. Discussion on examples, tutorials etc

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asdf
Posts: 9
Joined: Sat 11 Aug 2018, 08:19

Lumped elements dimensions and placement considerations

Post by asdf » Sat 11 Aug 2018, 13:28

Hi
I've got some problems with lumped elements. I tried to simulate 100R cooplanar line matched to 50R port with matching network (two 75R resistors) and finally I got reasonable results (SWR=1.2, measured is 1.1) but it required a lot of experiments with their size and placement (resistors in simulation much smaller than in real world but their height is not too low). In real world I matched the cooplanar line to VNA with "large" 0603 resistors but the the simulation seems to be much more sensitive to the matching network shape. Example attached.
Other example: 50R load connected to 50R source - I expect no reflection as long as I set 50R to port, load and calcPort but I don't usually get the SWR=1. In attached example I get SWR=1 when I set the impedances to 100R but when I change them to 50R or 200R then SWR is higher.
What do I do wrong? What to consider to get predictable results of simulation with lumped elements? I tried many combinations but still have no idea what makes the components working or not.
Attachments
cooplanar_100r_line_2_tmp7.m
(4.59 KiB) Downloaded 574 times
cooplanar_100r_line_6tmp.m
(3.29 KiB) Downloaded 569 times

thorsten
Posts: 1517
Joined: Mon 27 Jun 2011, 12:26

Re: Lumped elements dimensions and placement considerations

Post by thorsten » Sat 18 Aug 2018, 09:43

I have not (yet) had a look at your supplied files, but what is important is to have a propper mesh for the lumped elements, make sure they are oriented in Cartesian direction and that you do connect the end caps correctly. Maybe I can find some time to look at your files.

regards
Thorsten

asdf
Posts: 9
Joined: Sat 11 Aug 2018, 08:19

Re: Lumped elements dimensions and placement considerations

Post by asdf » Tue 21 Aug 2018, 01:16

In the long line matched with resistors I get low reflections as expected when I use 3D boxes as matching resistors. When I change their height to 0 then I get much higher reflection than measured. Is it something wrong or special about 2D resistors? I use 2D resistor at the end of the line as a terminator and there it seems to do the job (maybe coincidence?). I checked elements directions, priorities, mesh lines on caps and still can't see what's wrong

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