Advanced lumped-element trisection filter for digital microwave power amplifiers

In this paper, a compact lumped element bandpass reconstruction filter for digital microwave power amplifier applications in the 800 MHz band is presented. The filter, based on the trisection topology, includes a cross coupling which produces a transmission zero for maximum selectivity. In contrast to common filter designs the input impedance characteristic is optimized broadband to values different from 50 Ω, as is required for proper amplifier operation. The filter achieves an insertion loss of 0.8 dB and an equiripple bandwidth of 240 MHz, with improved out-of-band suppression.