A Diplexer-Like Dual-Band Filtering Power Amplifier With Selectable Frequency Output

This letter presents a novel diplexer-like dual-band filtering (DBF) power amplifier (PA). The PA is mainly composed of a diplexer-like DBF output matching network, which can better separate carriers into two output ports. In addition, the PA also integrates filtering characteristics, achieving better out-of-band and second harmonic suppression. For demonstration, a diplexer-like DBF PA (nonconcurrent) operating at 2.1/3.5 GHz is designed, fabricated, and measured. The measured small-signal maximum gains
$S_{21}$
and
$S_{31}$
in the lower and upper bands are 15.6 and 12.7 dB, respectively, and the isolation
$S_{23}$
between two output ports is lower than −22.2 dB. The suppression levels of one frequency output branch to another frequency band can reach −59.4 and −50.1 dB, respectively, and the second harmonic rejection levels are below −35.3 and −37.9 dB, respectively. The PA achieves the maximum efficiency of 62.4% and 51.2% with an output power of 41.0 and 39.5 dBm at two frequencies. In addition, using a 20-MHz long-term evolution signal with a 7-dB peak-to-average power ratio (PAPR) and applying the digital predistortion for the designed PA, the adjacent channel power ratios can be improved from −33.0/−27.5 to −52.7/−53.5 dBc at two frequencies.