What advantage does a pi-L network have over a pi-network for impedance matching between a vacuum tube linear amplifier and a multiband antenna?

A Pi-network is commonly used in amplifier output stages because it effectively matches impedance while acting as a low-pass filter. A Pi-L network improves upon this by adding an extra series inductor (forming an additional L-network), which provides a steeper filter roll-off. Because of this additional filtering stage, the Pi-L network achieves significantly greater harmonic suppression than a standard Pi-network. This keeps unwanted, out-of-band emissions from reaching the antenna. Distractors such as lower losses or higher efficiency are incorrect because adding extra physical components to the RF path actually introduces slight additional losses; the trade-off is made specifically for the superior spectral purity.