Reconstruction filters for switched-mode power amplifier systems

This paper presents two designs of reconstruction comb-line filters with symmetrical input for a class-S power amplifier system operating at 450 MHz. The class-S amplifier architecture is intended for highly efficient power amplification with demanding requirements for the design of the reconstruction filter terminating the final stage that operates in the push-pull current-mode. According to the measured results, the compact coaxial filters have insertion loss of less than 1 dB for the differential mode, a 3-dB-bandwidth of 27 MHz and a second pass-band at 2.8 GHz. The device can handle up to 300 W of input power and is mechanically tunable over at least one octave.