A Dual-Band Filtering Push–Pull Power Amplifier with a Large Frequency Ratio Employing a Hybrid-Mode Bandpass Response Balun

A dual-band filtering push–pull power amplifier (PA) with a large frequency ratio is presented in this paper. The proposed filtering power dividing/combining network is based on a hybrid-mode filtering balun using microstrip line (MSL) and substrate integrated waveguide (SIW). The MSL filtering balun operates in the S-band, with a frequency range of 2.6–2.86 GHz. Meanwhile, the SIW filtering balun is designed for Ku-band operation, covering a frequency range of 13–13.65 GHz. Under these conditions, the prototype is capable of attaining a frequency ratio as high as five times the original value. Due to the inherent differential characteristic of the hybrid-mode filtering balun with a large frequency ratio, the proposed push–pull PA not only realizes filtering functionality but also achieves second-harmonic suppression. To validate the designed concept, the proposed prototype has been designed, fabricated, and measured. Measurement results demonstrate that the proposed PA achieves a 7 dB small-signal gain while maintaining out-of-band spurious rejection during active testing. The developed dual-band filtering push–pull PA delivers excellent performance, with a peak output power of 36.8 dBm at low frequencies and 36 dBm at high frequencies. Moreover, by employing dual-band filtering baluns, the PA inherently suppresses even-order harmonics while simultaneously providing filtering characteristics in both operational bands, which effectively suppresses near-band spurious signals.