How to restrain 2nd harmonic in KW45 RF path design

[Annie_he]

Hi NXP team,

    Now we are developing a biluetooth board with KW45B41Z83, and we use connectiontivity Firmeve to control dut to do some RF test, and the test cmd as below:

and Then SA to get the signal successful, The power of carrier Frequency(2402Mhz) is 10.1dBm. 

But the 2nd Harmonic(4804Mhz) is out of the ETSI limit(-30 dBm/Mhz), our result is -22.9 dBm/Mhz.

So We want to ask you how can we restain the level of 2nd Harmonic in KW45 bluetooth design? Thanks.

best Regards,

Annie

[EduardoZamora]

Hello @Annie_he,

Hope you are doing well.

Could you please confirm that you have followed the KW45B41Z-EVK RF System Evaluation Report? Section 4.1.6.2 describes the test method and results for H2.

Transmit harmonic levels depend on the quality of matching components. I will suggest you taking a look at the Compact Planar Antennas for 2.4 GHz Communication. This document is focused on helping the customers understand enough board layout and antenna basics to select a correct antenna type for the application, as well as avoiding typical layout mistakes that cause performance issues.

Also, some recommendations to have a successful wireless hardware development RF circuit topology and matching, antenna considerations are described in the Hardware Design Considerations for KW45.

Regards,
Eduardo.

[Annie_he]

Hi Eduardo,

    Thanks for your response and sharing!

    I get The test method form ETSI EN 300 328 V2.2.2 (2019-07), and most setting is following the KW45B41Z-EVK RF System Evaluation Report.

    Our default inductance value in Pi circuit is marking in the picture, 1.5nH. And now we try to increase the value of inductance in Pi circuit to 2.0nH. Then the 2nd Harmonic is decreasing to -34.3 dBm, and it will pass based on ESTI rules.

     But we want to get lower 2nd Harmonic to get the certification.  Would you mind sharing the target matching which is most suitable for KW45? We have test the 2nd harmonic of the KW45-EVK, the value is about -40 dBm, which is ideal for us. Thank you very much.

  Best Regards,

  Annie

[EduardoZamora · Accepted solution]

Hi,

As mentioned in Compact Planar Antennas for 2.4 GHz Communication Application Note, Section 4.3 Impedance matching components, you can consult theKW45B41Z Evaluation Kit Board Design Files and use it as reference.

If re-tuning is required after using the EVK reference values, you could try replacing the series matching inductors with the next incremental values (up or down). You can adjust the tuning values as necessary.

Regards,
Eduardo.

[Annie_he]

Hi Eduardo,

    Thanks for your sharing for us. It help us a lot.

    Now we have decresing 2nd harmonic by tunning matching, and now 2nd harmonic is about -39 to -45dBm. But tx power is decreasing 0.5 to 0.7 dBm, RX sensitivty is getting 0.7dBm better. We want to get a balance between RF performence and 2nd harmonic.

   Best Regards, 

   Annie