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Antenna F reference design

Huber Jonathan
Prodigy 30 points
Other Parts Discussed in Thread: CC2590

Hi,

Is it nessesary that the wire lenght is the same and the 0 ohm resistor is placed on the refenece design of the CC85xx board? is the rule, the wire as short as possible?

The  distance from the gnd plane and the wire to the antenna, is this nessesary like in the reference design?

Thanks for helping.

regards

j. huber

  • 0
    TI__Guru 56590 points

    By wire do you mean the transmission line between the chip and the antenna? Usually it is designed to have a characteristic impedance of 50 ohm meaning that regardless of length it will not impose mismatch When source and load also is 50 ohm. You should follow the ref design as close as possible, but you can adjust the length of the line after the Balun and filter. 

    Can you specify which specific design you are referring to so I can see which 0 ohm you mean?

  • 0 in reply to Eirik V
    Prodigy 30 points

    Hi,

    it is the design CC85xx_cc2590EM from TI. The 50ohm load comes from the components, is that right?

    The wire is like an inductor and influenced the impedance. or is that insignificant?

    regards

    j. huber

  • 0 in reply to Huber Jonathan
    TI__Guru 56590 points

    Hello Huber,

    The Antenna together with the matching components form a load that should be close to 50 Ohm. The line has inductance, but it is more complex than that. Many parameters Width, depth, and metal type of the PCB trace in addition to distance between the copper on the layer beneath, the ground plane on each side and all the different characteristics of the PCB material itself will be variables that "control" the characteristic impedance. To get an idea of how the impedance change according to change in variables you can try out the TXLINE SW tool and change different variables to see how the impedance changes. One of the most sensitive variables I found was  the height between the layers. When you have shorter segments than 10% of the RF wavelength there is a rule of thumb that due to the very small phase shift over the line will make the effects of the characteristic impedance almost negligible. In this case just make sure to have a wide enough trace to minimize resistance ( results in loss ).

    When you say the 0-Ohm resistor, do you mean the resistor between the CC85xx and CC2590? If so this is a "do not mount" component meaning that you do not need to use it. The footprint was placed there to be able to add components for matching.

    My advice to you if you are not familiar with the details around RF theory is just to follow the ref. design as close as possible. This way you will have the best chance of getting a system that performs well. Also remember that if you use a different PCB type and have different distance between the layers in your PCB then the different parameters might change (For example antenna characteristics).