Wideband Class-F−1 Power Amplifier With Dual-/Quad-Mode Bandpass Response

Bandpass power amplifiers (PAs) are typically implemented by a cascade of second-order topologies. To achieve a wide and flat passband response, the number of resonators must be increased, which leads to large size, high loss and low efficiency, especially at high frequencies. In this paper, a wideband Class-F
^-1
PA based on a microstrip multimode bandpass impedance transformer (BPIT) is proposed. The modified quad-mode BPIT operation enables the creation of multiple transmission poles using only a single resonator, thus simultaneously achieving a flat wideband response in a small size. In addition, the drain bias and input feed line of the BPIT are arranged to satisfy the harmonic-impedance requirement of the Class-F
^-1
amplifier. Two PA prototypes have been designed, fabricated, and measured, which exhibit desirable filtering characteristics centered at 3.5 and 3.6 GHz for 5G applications. The fabricated dual- and quad-mode circuits demonstrate large-signal gains of 11.5 dB and 12.6 dB, maximum power added efficiencies (PAEs) of 67.4% and 66.3%, respectively and, with output powers greater than 38.5 dBm. For operation with a PAE larger than 60%, the PAs achieve bandwidths of 150 and 250 MHz, respectively.