A reflection-absorptive harmonic-rejection filter for RF power amplifiers

A novel reflection-absorptive harmonic-rejection filter (RA-HRF) is presented for harmonic-terminated high-efficiency RF power amplifier (PA). It basically consists of a pair of reactive band-rejection filter and a dual-band Wilkinson power divider where its isolation resistor absorbs the reflected signals from the band-rejection filters. The reflection-absorptive property can solve a parasitic anti-resonance problem between a harmonic-rejection filter and a harmonic termination circuit in a PA, which degrades the efficiency/attenuation of the PA/filter. Furthermore, the proposed RA-HRF has a low-loss property because of its structural symmetry and simplicity, compared with other conventional resistive/balanced reflection-absorptive filters. A Ku-band RA-HRF for suppressing 2^nd-harmonic of an X-band PA has been fabricated, and the reflection-absorptive/low-loss characteristics have been confirmed experimentally.