Low pass filter does not take effect

Hi Experts
In my WiMAX RF design, I used a low pass filter after power amplifier to remove 2nd and 3rd harmonic.
Unfortunately, the LP filter doesn't take effect because it only can filter out 3rd harmonic by 20dB rather than 40dB which the LPF demo board can get.
Does any expert know what wrong with my design?

Thanks

Hello,


Your LPF is designed for a 50Ohm match at the 2nd and 3rd harmonics, which is surely not the case on application boards. That should explain the difference observed on the attenuation between application and demo baords.
Hope this helps.