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IWR6843: waveguide trace width + ground separation calculation

Ryan Sarver
Intellectual 540 points
Part Number: IWR6843

I'm currently working with a PCB manufacturer to design a custom radar board based on the IWR6843ISK. I'm planning on copying the antenna design from the development board as it meets the requirements of our application.

When they run the stack-up simulation using their Polar design tool, the resulting trace width (with an 8mil ground plan separation) is smaller than that used in the TI design, 6.3mil vs 7.795mil used for the ISK.

Using the 7.795mil trace width, an impedance of 46.3ohm is calculated.

Any idea where these discrepancies could be coming from?

  • 0
    TI__Mastermind 25835 points
    Ryan,

    RF traces are designed to be 50 Ohm impedance with the GCPW topology. At mmWave frequency the numbers calculated using Polar design tools may not be that accurate as compared to full wave 3D EM solver based solution, there are many other factors that we need to consider for the impedance matching.

    They don't calculate effective Dk values at mmWave frequencies, also there are other factors that affects the Dk value such as surface roughness, type of Cu used, operating frequency etc, that will affect the impedance. Typically these are comprehended in 3D EM simulator (Such as Ansys HFSS, CST or any equivalent 3D EM simulator) tools and from that PCB geometry's are optimized to get 50 Ohm transmission line impedance matching.

    You could mention in the FAB note to adhere to these targeted dimensions for the RF traces for the PCB fabricator.

    Thanks and regards,
    CHETHAN KUMAR Y.B.