QUESTION

Question

We are designing an IoT board for worldwide cellular coverage, and due to small GND plane we want to apply aperture tuning to the antenna in order to meet performance requirements, especially in the lower bands. With PCB size of only 40x60 mm how would you go about. I can see that for example Lucida SR4L002 has a tuning inductor between GND pad and GND plane.
Our idea in such a case would be to design in a SP4T switch, for example Infineon BGS14PN10 to change between tuning components in order to switch between different tunings for the lower bands. How should we proceed with design and board layout for such an approach?

Or is it other, better ways to achieve this?

Answer 1

A part of the answer is already given here: https://ask.antenova.com/567/matching-sr4l002-antenne

Have a look at the datasheet of the antenna. 40 x 60 mm regrets that the PCB is only 50 mm long. At 50 mm length, you might not reach the bandwidth for band 71, 20 or even 8. Before you can work with a switch you have to reach a band first. First, make a test setup with case and battery without any other components and then you can continue or maybe enlarge the PCB.

Comments

Hi,

Thanks for the response. We already have a 60x40 mm PCB based on a different antenna that is tuned for B20. The reason for considering to switch antenna is to use one that has a tuning component on a dedicated pin, to be able to switch between different tunings for the antenna.
What I am less sure about is how we woud proceed with layout in this case.
Of course we expect to loose quite a bit of efficiency only having an effective GND plane of 50 mm.

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Hi Ola, my business friend Günther Klenner explained what is to do. If you can not do this on your own, then Günther or I will do this for you.

Answer 2

Hello Ola,

Similar to Lucida SR4L002 with the ground return components, our Inversa SR4L034 antenna has information in the data sheet that will help you in setting up the active switching circuit you are referring to starting on page 22. Please let me know if you need more information than this.

Best regards,

Geoff Schulteis

Answer 3

One method of making your PCB ground plane area seem to be bigger is to consider including any metal mounting bracket or fixed cable shields as extensions of your PCB GND.  You will need to tune and match your antenna with those things in mind.

We have been able to utilize this method for some electrically small antennas in the past.

Answer 4

As Harald already mentioned you may need active antenna tuning to trim your antenna to used band. Prepare yourself also for an active antenna matching at desired frequency (2nd or 3rd switch) to adapt matching.

Another point is the verification. On such small GND plane your test cable to VNA can easily detune your antenna. Special precausion needs to be take to avoid this.

PS: If you have access to MIPI then some SP4T swiches from Infinion allow up to 16 combinations.

Answer 5

Hi Ola,

I have meet similar issue in one of our application. Do You have a possibility to enlarge Your PCB for 40x70? In that case Integra or Latona also would be a good choice.
May I ask where are You from and which bands You would like to cover?