VNA Test Connection to Reference Design

RE: VNA Test Connection to Reference Design

ketiljo — Wed, 07 Oct 2015 11:49:57 GMT

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.

RE: VNA Test Connection to Reference Design

chalecampb — Tue, 06 Oct 2015 15:23:16 GMT

Hi,

I am sorry I might not have been clear, but this is to explicitly perform antenna matching. We do have a spectrum analyzer, but that cannot provide the VSWR measurements that I need to select the components required for manufacture.

Thanks, -Alex

RE: VNA Test Connection to Reference Design

ketiljo — Tue, 06 Oct 2015 08:55:20 GMT

Hi Alex

You shouldn't use a VNA for this. It will only tell you the impedance when you look into the matching network. It will not give you any information about the actual output power, the level of the harmonics or spurious in RX mode. It's far better to use a spectrum analyzer and measure all these parameters.

Setup a constant carrier and measure output power and harmonics at the same time. For this, you can use the SWF cable if you have the same connector on your design as on the nRF51-DK.

A VNA is usefull for antenna measurements. You calibrate the coax cable with your cal kit as usual. Consult the operating manual for the procedure. Then you need a short test cable with a suitable connector in one end. The other end should be open. Setup the VNA to measure impedance and add electrical length (in the calibration menu) until you measure open, or near open, impedance. Then, solder the cable to the board. The center conductor should be as short as possible, 1 mm or so. You need to break the connection between the antenna and the matching network and solder the cable to the antenna side. Make sure the outer conductor is firmly connected to the ground plane.