pcb calculator incorrect results for transmission line

[Heitor]

Coupled Microstrip Line in TransLine tab of PCB Calculator does not agree with online calculators.

With:
T = 1.2 mil
H = 1.5 mm
W = 0.5 mm
S = 0.5 mm
Er= 4.5

PCB Calc says Z_odd = 68.8 Ohms
EEWeb Calc says Z_odd = 76.4 Ohms
AllAboutCircuits says Z_odd = 76.4 Ohms

Attached PCB Calc screenshot.
Calculators:
https://www.eeweb.com/tools/edge-coupled-microstrip-impedance
https://www.allaboutcircuits.com/tools/edge-coupled-microstrip-impedance-calculator/

I did not check the other transmission line calculations.

Application: kicad
Version: (5.0.0-rc2), release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.60.0 OpenSSL/1.1.0h zlib/1.2.11 libidn2/2.0.5 libpsl/0.20.2 (+libidn2/2.0.4) nghttp2/1.32.0
Platform: Linux 4.17.3-1-ARCH x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
    Boost: 1.66.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.60.0
    Compiler: GCC 8.1.0 with C++ ABI 1012
Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_WXPYTHON=OFF
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON

[Seth Hillbrand (sethh)]

The simplistic online calculators are frequency independent. Increase your modeled frequency in KiCad to see the effective frequency used by the online calcs.

[Gabriel Staples (ercaguy)]

In other words, the KiCad calculator in this case at least is better, and should be trusted over the online calculators, correct?

[jean-pierre charras (jp-charras)]

@eRCaGuy,

Please, avoid this kind of stupid behavior.

Impedance calculations are always approximations depending on formulas used to do these calculations, that never are exact formulas, due to the complexity of the problem.

You could try Saturnpcb that is a very good tool.

[Maciej Suminski (orsonmmz)]

eRCaGuy, do not trust anyone, make your own judgements - KiCad developers are still only humans.

[Wayne Stambaugh (stambaughw)]

Isn't that engineering 101?

On 7/10/2018 1:50 PM, Maciej Suminski wrote:
> eRCaGuy, do not trust anyone, make your own judgements - KiCad
> developers are still only humans.
>