VNA Test Connection to Reference Design

[chalecampb]

Hi all,

I need to be able to check the matching networks on a design using the nRF51 series chip. My understanding of the procedure is,

1. Set up the board, enclosure, etc. and the cabling
2. Calibrate the VNA to account for the cabling impedance
3. Perform VSWR measurements on the board under test

My confusion is with part 2. What I have found is that

• SWF is not usually adaptable from an N-type standard VNA connection
• SWF Male connection is not usually provided on calibration loads
• There are no adapters from SWF to N at all, or SWF to SMA with cables

Do people usually swap J1 in the reference design with an SMA connector? If not, my test setup is going to look something like

• N-Type to SMA Cable -> SMA to SWF Cable -> SWF Male to MM8130-2600
• N-Type to SMA Cable -> SMA to N Adapter (no cable) -> Calibration Load

My concern is that the calibration load is not going to account for the SMA to SWF cable, and I do not understand why this is not an issue. I am also concerned that the SMA to N adapter will differ in characteristics from the SMA to SWF cable. What kind of error would this introduce? Are we talking 1% or 30%? For reference, the SMA to SWF probe cables associated with the MM8130-2600 female SWF connector is 12" long.

Is SWF referred to by any other connector series name?

I also checked Nordic's recommended test setup white paper, and they listed overall requirements and suggestions, but didn't provide cables or part numbers for the cables.

What does everyone typically use for the VNA connections?

Thanks, -Alex

[ketiljo]

If you want to measure and match the antenna, this must be done after the connector, not looking into the matching network. You have a defined 50 ohm plane. Measure the radio part (matching network) with the spectrum analyzer and the antenna part with the VNA.

Note that the matching network components can not be used to tune the antenna, you need additional components for that.