2
\$\begingroup\$

I have an active RF antenna that is powered through an inductor in a bias tee network.

schematic of coax antenna connection, inductor connected to power, and DC-blocking capacitor to the receiver

How should I draw it on PCB layout?

I have 3 ways to do that. In these layouts, up is capacitor, bottom is connector for antenna, right is inductor.

  1. With a T join trace from the inductor

enter image description here

  1. With the inductor on the RF trace

enter image description here

  1. With the inductor on the far side of the connector

enter image description here

My signal is 1...2 GHz. What's the better/worst solution?

\$\endgroup\$
  • \$\begingroup\$ I inserted the frequency range you mentioned in a comment. You should add is the signal narrow band or does it cover full 1 to 2 GHz band. In addition you shoud tell something of the dimensions and materials. It's well possible that the wavelength for 2GHz is only about 2 cm if the PCB permittivity is high enough. Then a few millimeter wire can cause a catastrophy if it's not properly designed. \$\endgroup\$ – user287001 Nov 30 '19 at 22:38
  • \$\begingroup\$ Note: you might be helped by keeping copper away from your inductor, particularly the ground plane fill. Otherwise you get more capacitive coupling across the inductor pads on the board. \$\endgroup\$ – user2943160 Nov 30 '19 at 23:55
2
\$\begingroup\$

I am going to make an analogy to DC biasing the collector of a microwave power amplifier. I think that the main selection criteria would be the Noise Figure here, but I am rusty there to do the calculation.

I would go with the T join. That is what I see in microwave biasing stages. The length does not seem to matter much, since there is a huge inductance in series. (There is a quarter wave trick to increase isolation there.)

On the line makes an abrupt change to the signal path, which will alter Z0.

On the other side is odd, but might be interesting. But I have never seen it.

|improve this answer|||||
\$\endgroup\$
  • \$\begingroup\$ Thanks for this answer. Quater wave length will be difficult as my signal is from 1 GHz to 2 GHz. \$\endgroup\$ – doom Nov 30 '19 at 20:27
  • 1
    \$\begingroup\$ In such small frequencies, I guess you would easily get away with it. \$\endgroup\$ – mehmet.ali.anil Nov 30 '19 at 20:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.