P822601 Internal PCB Antenna Poor Performance vs External Antenna on nRF9151

[Piyush Devani]

Hi,

nRF9151 + Kyocera AVX P822601 internal SMT antenna: 8 dB RSRP loss vs external antenna — possible PCB layout issue?

Test Results

Test 1 — Out of Faraday cage, internal P822601 antenna:
WR-2370 CONNECTED — RSRP: -66 dBm, RSRQ: -5 dB

Test 2 — Out of Faraday cage, external Taoglas FXUB65.07.0180C via SMA:
WR-XXX-2149 CONNECTED — RSRP: -65 dBm, RSRQ: -6 dB

Test 3 — Inside Faraday cage, internal P822601 antenna:
WR-2370 FAILED — no message received

Test 4 — Inside Faraday cage, external Taoglas FXUB65.07.0180C:
WR-XXX-2149 CONNECTED — RSRP: -65 dBm, RSRQ: -6 dB

Reference device for comparison:
WR-8738 (Taoglas FXUB65 external) CONNECTED — RSRP: -58 dBm, RSRQ: -5 dB

Summary of Issue

• Approximately 8 dBm RSRP difference between internal P822601 and external Taoglas FXUB65 antenna
• External antenna works reliably inside Faraday cage
• Internal antenna completely fails inside Faraday cage
• Both devices use the same nRF9151 SiP and same firmware
• RF switch configuration confirmed:
  • R42 = DNP
  • R43 = 0Ω (internal antenna path active)

We designed the RF layout same as the Nordic nRF9151 DK board reference design.
https://devzone.nordicsemi.com/support/348377

Attached Files:

• Schematic (RF section)
• PCB layout
  drive.google.com/.../1tCCkOSTPwavuZT4Ztj6aebqibDN27iHo
  

Thank you for your support. We look forward to your guidance and hope you can help us resolve this issue.

[JONATHAN LL]

Hi there Piyush, 

I see you are getting some good feedback in the other ticket here but I will try and provide some answers here as well. 


Firstly I think this is a issue that you need to bring up with the antenna provider as well. We at Nordic have little we can do with the antennas here as we only use them as other customers also would, the ones we use on our development kits are likely chosen due to a different set of criteria then what some end customer products would have. 


The antennas will have different performance characteristics depending on its surrounding environment, and a Faraday change will have in most cases a negative impact on antenna as it will in best of cases only provide a hindrance but can block as well. The two antennas used here also work a bit differently where the PCB antenna will likely be more effected by the PCB shape and size, this can change the radiation pattern but also the performance over different frequencies. The external antenna is likely less effected by the PCB shape and size. 

During testing is the antennas located in the same place relative to the Faraday cage? if not this will also be a contributing factor to why these antennas my perform different in your test setup. 


I would contact the antenna manufacturer and start a discussion with them on what is the best practices for the setup you have here and its conditions. They should be able to provide proper guidance and set a realistic expectation on what can be achieved with their antennas. 

The nRF9151 is not the issue here as it proves it can work well in the test conditions with at least one antenna. 

Regards,
Jonathan