QUESTION

Question

The Product Specification for the SRF2I019-PS-1.7  PFC antenna shows a return loss plot on page 3. How was this measured? At the antenna directly or at the end of the 100mm cable? 

I have measured this antenna with my VNA (S11) at the input to the 100mm cable and the result is very different, see below.

Please advise.

Thanks,

Jim

Answer 1

Hi Jim,

It's difficult to see in the image you provided. The antenna must be adhered to a plastic surface, as stated in the tabulated data, otherwise it will look off-tune. The antenna is designed in this condition, as this is how it will be practically fitted in a device. Is the antenna adhered to a suitable surface?

Many Thanks

Steve

Answer 2

Hi Steve,

The antenna is attached by adhesive to the inside of a plastic enclosure. I believe the material is polypropylene but I'll check and confirm. I will assume then the measured return loss plot in the product specification is measured at the cable (100mm) connected to a VNA, is this correct?
I will extend the span of my VNA measurement to determine if the antenna is off frequency. This may be why my S11 measurement starts to decline below 800MHz.
Best regards,

Jim

Answer 3

Hi Jim,

Thanks for confirming, yes this was measured with 100mm cable fitted. The measurement was made from a small PCB acting as a host interface. I.e.: Connect VNA to host PCB at the feed to the UFL socket, set Electrical Delay, attach antenna, measure.

Many Thanks

Steve

Answer 4

Hi Steve,

I made a second VNA measurement with a wider frequency range (500MHz to 1000MHz) and the S11 response has a minima at 762MHz.So there is an extreme downward shift in the frequency response of the antenna in the enclosure. The material that the antenna is mounted on is Thermoplastic Polyurethane (TPU). I should get the material properties this afternoon and can forward that to you. The image below shows the S11 plot with the center frequency about 750MHz. The three markers on the right (blue trace) identify where the response should be.

Is there some way to shift the frequency response upward with a material buffer between the antenna and the TPU or some other solution? 

Best regards,

Jim

 

Comments

Hi Jim,

A material buffer will probably not have much effect. It may be due to the antennas proximity to conductive/reflective parts, or the cable routing. I have contacted you directly, as I would like to get a few more details on your set up/device.

Many Thanks

Steve