I am designing a Class-E power amplifier in UHF band using ADS. Now I have 20dBm fundamental output power with 13% PAE, which is low for this class of PA. The problem is that I have thermal dissipation and DC power consumption and harmonics. How can I reduce these?
Class-E implies switching a transistor on and off, rather than operating it linearly. This implies a rectangular signal shape, which implies a sinc spectrum, which implies high out-of-band emissions. You counteract that correctly by using High-Q LC filters. Make sure you measure efficiency at the right point -- that is, including these filters, as they convert harmonic energy to in-band energy, if you want so.