0
\$\begingroup\$

I am designing a GPS module but am quite new to RF design. I have seen a number of people say to keep your antenna feed line as short as possible. But in the design guide of the GPS module I am using, it says for chip antennas, which I am using, keep the module a minimum of 2 cm away from the antenna.

enter image description here

Also, the datasheet for the chip antenna I am using shows a long winding trace for the feed line.

enter image description here

I have several components in between the feed point and the RF IN pin on the GPS module, such as blocking capacitors, LNA, SAW filter, and frequency tuning inductor. I have placed the GPS module about 7 cm away from the antenna, placing all the components in between like this.

enter image description here

Which design rule should I obey more closely? Trying to keep the GPS module at least 2 cm away from the chip antenna? Or keeping the RF traces as short as possible? Also I would welcome any other comments or criticisms of my design.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ Having PCB copper above the corner antenna pattern will possibly affect the reception pattern. Better to eliminate the copper and even move J20 away from the antenna end. The minimum distance mentioned in the specification is likely needed to reduce noise pick up to or from the chip circuitry. \$\endgroup\$
    – Nedd
    Apr 22, 2022 at 4:18

1 Answer 1

1
\$\begingroup\$
  1. Optimize positioning of the antenna on the PCB: it should be at the upper right corner, not halfway up the right edge.
  2. Minimize bends and jogs in the microstrip transmission line. Every discontinuity is a potential source of reflections and loss. Just one bend at the lower right corner should be sufficient.
  3. The LNA/SAW components should be as close as possible to the antenna so that transmission line losses don't degrade the noise figure.
  4. Move all the power and digital headers to the far left end of the PCB
  5. Rotate the GPS chip so the antenna output emerges at the lower right corner and can connect directly to the transmission line. Moving it to about the middle of the board will provide sufficient isolation from the antenna while leaving room to keep the DC/signal headers all on the left end.
\$\endgroup\$
1
  • \$\begingroup\$ Thanks again for your valuable input. \$\endgroup\$ Apr 22, 2022 at 13:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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