Harmonic filtering is implemented in two stages: the second harmonic notch filter and the higher order harmonic low-pass filter.The notch filter is implemented by replacing the original L3 with a parallel LC filter. As a general rule of thumb, the new inductor value is chosen to be 3/4 of the original L3, and C4 is calculated to resonate out the second harmonic of the carrier frequency.The higher order harmonic filter is a 50-ohm to 50-ohm pi filter, realized on C5, L4, C6, and C7. C5 is therefore used for both the impedance matching and the harmonic filtering, and its value will be the sum of the two values obtained separately.Again, it’s often necessary to fine-tune the simulated values to account for PCB parasitic and practical component values.The last step would be to add the PE4259 RF switch and redo the measurements. Additional filtering and impedance matching to any non-50-ohm antenna can be accommodated by utilizing C8, C9, L5, and C10.