According to the first attached figure you are including dispersion effects. How does the impedance, seen from the load looks like?
If I understood you correct, for both simulations the load impedance is 12.2 Ω?!
Because i've never used smith chart in cst before the values on the right part of the smith plot inside the parentheses what are they stand for?View attachment 158912View attachment 158913
Is it possible that this happened because W/h>15?? Because if i want to use waveguide port(although i'm using discrete port) and calculate the port extension coefficient it produces an error wich says that w/h>15
Because i've never used smith chart in cst before the values on the right part of the smith plot inside the parentheses what are they stand for?View attachment 158912View attachment 158913
The "," decimal indicator is located at the values of Z0 and epsilon effective wich are produced by the impedance calculator of CST. As for the input values of line width, substrate height and metal thickness i used "." decimal indicator so the produced values are fine.I dont know, but it seems there are some restrictions in CST, and I have no clue which one. It sounds to me your ratio is physically some kind unrealistic.
You have not told as If you have tried to unify the decimal indicator in your calculations, and if it results in different results.
Sorry at the beginning i meant to write the values at the left side of the smith chart not the right(made a typo)That may also be the referece impedance for the smith chart, if so, your result for the compolete matched 12.2 Ω system should reside in the center of the smith chart.
We get the same 12 Ohm for w=1.5mm h=0.1mm from other micorstrip calculculators, so that part is ok.
But see my comment in #8 on port width ... There is a strong discontinuity when such a very wide line is connected only in the line center (by lumped port). You need something like a wide resistive sheet (same width as line) for termination.
the values at the left side of the smith chart
a warning from Momentum wich says that the port becomes electricaly large above 10.25 GHz and the S parameters may become unphysical so i cannot trust the results i'm getting(wich are different from the results i got from schematic).
Sorry at the beginning i meant to write the values at the left side of the smith chart not the right(made a typo)
The screenshot of the current density of the line is attached, but it doesn't seem physicaly correct because from what i'm seeing there, is that there are some extremes at the edges and at the rest of the line the density is much lower, looks like a standing wave at the two edges. Also very weak signal appears to travel to port 2. It looks like more of a cavity than a transmission line. Also, besides of the warning about the electrically large port, i get two more warnings about the substrate and layout(screenshot is attached)- - - Updated - - -
Yes, the line must NOT be wide compared to the wavelength, otherwise you get funny resonances and multi-mode issues in both simultation and reality. So have a look at current density that you get from Momentum, if that looks physically correct.
Placing the pin on the edge of the line is fine, that is what you want to have here - if it matches your physical reality. See my appnote on that topic:
https://muehlhaus.com/support/ads-application-notes/edge-area-pins
The values in the parenthesis on the left are your complex impedances Z = R + j • X. The fist one (left) is the real valued part (resistance) and the second one (right) the complex one (reactance).
According to this values, the reference impedance of your smith chart should be 12.2 Ω (center corresponds to 12.2 Ω).
that there are some extremes at the edges and at the rest of the line the density is much lower, looks like a standing wave at the two edges. Also very weak signal appears to travel to port 2. It looks like more of a cavity than a transmission line.
Also, besides of the warning about the electrically large port, i get two more warnings about the substrate and layout(screenshot is attached)
The screenshot of the current density of the line is attached, but it doesn't seem physicaly correct because from what i'm seeing there, is that there are some extremes at the edges and at the rest of the line the density is much lower, looks like a standing wave at the two edges. Also very weak signal appears to travel to port 2. It looks like more of a cavity than a transmission line. Also, besides of the warning about the electrically large port, i get two more warnings about the substrate and layout(screenshot is attached)
View attachment 159008View attachment 159009
Yes, the minus pin is assigned to GND just as port 1
View attachment 159015
Screenshots of S11 and S22 from 0-33GHz and Smith charts of S11 and S22 at these frequencies are also attached (first two screenshots)@nikosnte
I would like to see the S-parameters down to 0Hz, so that we can better check for simple mistakes in the setup.
The simulation was performed for the band 27-33 GHz. The central frequency is 30GHz. The line has characteristic impedance 12.2 Ohms and load impedance also 12.2ohmsHi, for which frequency was the simulation performed? 30 GHz for the 12.2 Ω line with a 12.2 Ω load and source?
Yes, weird thing that the input impedance at 33 GHz is greater than charecteristic impedance wich for a line with ZL=Z0 it is mathematically impossible.According to your attached smith charts, the impedance seen from the source is higher than expected (@ 30 GHz), thus a missmatch and consequently multiple reflections and standing waves occuring along your microstrip.
I attached the current along the microstrip for the case at wich i used a discrete face port. As volker said, it makes sense that because of the wide line it is incorrect to place a lumped port as an excitation and i also placed a lumped port as the load so maybe there are some reflections also there. Next to the currents i attached the S11 parameter of the lumped port case. Something else interesting, is that i simulated the same line 1)with a substrate and ground plane with bigger width and 2) with a substrate and ground plane with the same dimension of the line and the results were much different. I also attached the screenshots for these two cases.First screenshot shows the current for the lumped port case and the rest of them is for the two other cases in that orderWould it be possible to provide two 2D line plots, one showing the current along the microstrip line as well as one showing the voltage? As your transformed load appears to be larger than the source impedance (@ 30 GHz), I would expect a "high" voltage in combination with a low current at the load (smiliar to a open circuit condition).
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