Which network configuration provides the most effective harmonic suppression?

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Harmonic suppression is achieved by shaping the output network so that harmonics see a path to ground or are otherwise blocked, while the fundamental remains well-matched to the load. A Pi-L network does this effectively by combining a low-pass filter structure with an impedance-transforming section.

The Pi portion (two capacitors to ground with a series inductor) acts as a low-pass filter. At the fundamental frequency, the capacitors present relatively high impedance, so they don’t load the signal. At harmonic frequencies, their impedance drops, providing a path to ground and attenuating those harmonics before they reach the load or radiate. The added L section tunes the circuit to improve the overall attenuation pattern and maintain a good match at the operating frequency, giving deeper and broader suppression of harmonics than a single Pi or L network alone.

A simple L-network is mainly about impedance transformation and doesn’t inherently provide strong harmonic filtering. The inverse L network is used in different matching scenarios and isn’t optimized for broad harmonic suppression. By combining the filtering action of a Pi network with the tuning capability of an L section, the Pi-L configuration delivers the most effective harmonic suppression.