Bandpass Filtering Power Amplifier With Wide Stopband and High Out-of-Band Rejection

In this brief, a power amplifier (PA) with excellent integrated filtering characteristics is presented. The designed process is based on a novel impedance transformer (IT) consisting of cascaded coupled-line sections with stubs. The proposed IT generates four transmission zeros (TZs), which not only greatly improves the frequency selectivity, but also improves the second harmonic suppression performance, further enhancing the linearity of the PA. For demonstration, a bandpass filtering PA is designed, fabricated, and measured. The designed PA exhibits both good filtering bandpass response and power amplification. The rejection levels are larger than 59.7 and 69 dB for the lower and higher suppression bands. Meanwhile, the measured drain efficiency (DE) of the constructed PA is 58.5%-73% with a large-signal gain of 8.9-10.2 dB at 1.85-2.1 GHz. Besides, using a 20 MHz long-term evolution signal as the driving signal for the PA, the adjacent channel power ratio is lower than −57.8 dBc.