Abstract
This brief presents a co-design of the second harmonic-tuned broadband power amplifier (PA) in cascade with a stub loaded parallel-coupled lines microstrip bandpass filter. These coupled microstrip lines are bilaterally connected with the shorted stub. Filter parameters are determined by an even-odd mode impedance analysis to ensure the high-selectivity and anti-interference bandpass response. Hence, a proper fundamental and second harmonic impedance matching is realized in the desired regions of the Smith chart. Moreover, an overall circuit size is significantly reduced with easy integration. For validation, the proposed structure is manufactured and tested for a commercial 10-W GaN transistor across 1.6-2.8 GHz (54.5%), with 49.1%-65% measured drain efficiency (DE) and 38-41 dBm of measured output power has been obtained. Also, when this PA-filter circuit is driven by a 5 MHz long term evolution signal with a peak to average power ratio of 8.2 dB, an adjacent channel leakage ratio of lower than -55 dBc is achieved.