QUESTION

Question

When connecting a VNA to the PCB with a coax "pigtail", the outer ground of the coax affects the ground plane and changes the measured impedance of the antenna. What type of test setup do you use to reduce this effect?

Max Hendrickson

Answer 1

I will use  smallest possible  cable   and positioned  outside of the  PCB area. In possible scenario will connect SMA/ small RF  connector directly connect  to the PCB antenna trace after tuning circuit . Need to plan during PCB design to the extend possible

Answer 2

When tune an antennas there should always cut out measuring systems GND. A cable ferrite bead is one easy way.

Answer 3

We use special pigtail cables with U.FL connector and Balun in the cable. This will avoid current in the shielding of the cables. If you drop me an email then we will maybe sell a pair to you. harald.naumann (at) lte-modem.com

Comments

Hi Harald, I have to tune the antennas for both 868MHz and 2.4GHz. What is the frequency range that your special cable works (maybe it depends of balun,right?)? Can you show to me the special pigtail cable? It is possible to tune the antenna with a special calibration of the plane of the measure. Maybe in this way you can take into account the effect of the system GND. Thank you.