Telit GE863-GPS interface (for EVK2): 50 ohm impedance matched antenna microstrips?

3 thoughts on “Telit GE863-GPS interface (for EVK2): 50 ohm impedance matched antenna microstrips?

  1. consideration 1:

    microstrip line
    impedance for a given technology (PCB) depends basically only from
    the strip width.

    consideration 2:

    GSM antenna feed
    line impedance shall be 50 ohm

    consideration 3:

    GPS antenna feed
    line impedance shall be 50 ohm

    I can deduct from considerations 1+2+3 that GSM and GPS
    microstrips shall have the same width.

    Observation:

    take a look at the
    Telit_EVK2_User_Guide_r9 > Figure 24: GE863 Interface Boards:
    GE863-GPS (at center) page 42of 94:GSM microstrip width is sensibly
    different from GPS microstrip width.

    Question:

    What is wrong? My deduction?
    my observation? Telit GE863-GPS interface PCB layout?

     

    Thanks in advance. for any support.

    1. You are right, however you can see the lengths are very different, even in theory this wouldn’t make a difference, the interferences with nearby components may affect, and the microstrips were tuned with live measurements.

       

      1. It is not easy to explain but the width of the RF line depends also to the thickness of the PCB and the distance between RF line and its ground reference  . If the GND is closer to the RF line then the strip line will be tighter as well as the distance between strip line and the adiacent GND plane will be tighter. So in the specific case (GE863 interface board)  the RF dimensions are different because the distance between RF lines and related GND plans are different (GND planes are placed in different layers of the PCB, mainly to shiled the RF signals and avoid mutual interference interferences).