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This article presents a high-efficiency dual-band filtering Doherty power amplifier (DPA) using multi-function circuits for simplifying the structure. A dual-band filtering power combiner also plays the role of real-to-real impedance matching, in which one resonator is shared by both the power combing and filtering circuits. Thus, only one extra resonator is needed for the power combiner to provide second-order dual-band filtering responses, which contributes to high efficiency of the DPA. Transmission zeros are generated between the two passbands, realizing a sharp roll-off rate and greatly enhancing the isolation between the two passbands. Meanwhile, an impedance control network is designed to simultaneously suppress the harmonics and transform the optimized complex impedance desired by the transistor to a real one. In this way, the output matching network and extra filter in conventional design are realized by the filtering power combiner and impedance control network in the proposed design, resulting in a simpler structure. A dual-band DPA operating at 2.14 and 2.6 GHz is implemented with the measured peak efficiencies of 64.4% and 69% at the output power of 43.25 and 43.3 dBm, respectively. The 6-dB back-off efficiencies are 50% and 57% at the two passbands. Under 20-MHz long term evolution (LTE) modulated signals with a peak-to-average power ratio (PAPR) of 7.5 dB, the DPA after digital predistortion (DPD) is measured with an adjacent channel leakage ratio (ACLR) of better than −45.2 dBc and the efficiencies of 51.6% and 54.3% at interested bands. The peak efficiency under the excitation of the concurrent modulated signal is 48.6%. [ABSTRACT FROM AUTHOR]

In this article, we propose a circuit model for designing the switchable filtering circuit with reconfigurable functions between a single-pole quad-throw (SPQT) filtering switch (State 1) and a four-way filtering power divider (State 2) without additional switchable impedance matching network (IMN). The proposed circuit model can be utilized as the feeding network of a switchable directive and omni-directional antenna system to eliminate the omni-directional antenna in conventional solutions to reduce the size and cost. It consists of four filter channels with a common port. In State 1, it works as a SPQT filtering switch, where only one channel is turned on to realize good filtering responses and the impedances at the other three channels are adapted to infinity to realize high isolation. The four channels are turned on simultaneously in State 2 to work as a four-way filtering power divider, and the input impedance of the common port is the same as that in State 1. Thus, a switchable IMN is not required for port matching when switching between the two states. Transmission zeros are generated to enhance the skirt selectivity. For verification, the filtering circuit is constructed using high- $Q$ coaxial resonators. Experimental results show excellent performance in both states acting as a SPQT filtering switch and a four-way filtering power divider. [ABSTRACT FROM AUTHOR]