QUESTION

Question

Dear sir/madam,

PCB vendor have finished our M20057-1 board. Now we can tune M20057-1 module antenna matching.

In our experience, we understand how to tune passive antenna. But we have no experience to tune your active antenna. Do you have any simple guideline (or step) for your GNSS module matching tuning? Can I use network analyzer to tune M20057-1 GNSS antenna matching tune?
my step(I am not sure):

1. Apply 3v to M20057-1 Vcc and then network analyzer connect to RFO capacitor.
2. measure RFO return loss.
3. What components value(in AT1 and AT2) can be use when I tune the matching?

Thanks in advance.

Best regards

Harry Cheng

Answer 1

Hi Harry,

Tuning active antennas is similar to passive antennas you just have to supply DC voltage to the LNA to turn it on.

For the tuning values of AT1 and AT2 you should start with a zero ohm resistor on AT1 and a 1.8nH inductor on AT2. The series capacitor, C1, acts as a DC block going to your network analyzer with a value of 22pF so be sure to put this in your circuit or you can damage your network analyzer.

Be sure to follow our VCC component values and install the ESD diode as well listed in our datasheet. Other than that be sure the 3VDC is turned on when matching otherwise you will get the wrong results.

Hope this helps but if not feel free to reach out to our tech support line for any additional needs.

Best regards,

Geoff S.

Comments

Dear Geoff,

Thanks for your quick reply.

I follow your method to tune antenna matching and apply 1.8v series 47nH inductor to RFO. But I found return loss is about +5dB at 1596MHz. Is there any mistake in my setup?

I also change AT1 to 15pF and AT2 to 2.2nH. But return loss is also about +5dB at 1596MHz.

I apply 1.8v. The return loss is below:

---

I do not apply 1.8v. The return loss is below:

Answer 2

Hi Harry,

Yes, the smith chart on the network analyzer will go off the chart because you are sending in more power than it is putting out on the RF port so the image you sent where the trace goes outside the circle is accurate and typical.

Your tuning with the 1.8VDC turned off looks good as it is -10dB across the entire band.

Have you taken your GPS receiver outside to see how well it works? That would be my next step.

Best regards,

Geoff S.