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In this brief, for the first time, the design of a dual-band pseudo-Doherty load-modulated balanced amplifier (DB-PD-LMBA) with two arbitrary frequency bands is presented. It is accomplished by the adoption of generalized dual-band coupler and power divider. Besides, for size reduction and design simplicity, the finite off-state impedance of the active devices is fully utilized for removing the offset line, and conventional dual-band phase shifter is eliminated by employing an appropriate matching network design. In addition, a stop band between two target bands is introduced to enhance isolation. For validation, the proposed PA, operating at 1.5 GHz and 3.2 GHz, with a 10 dB OBO, was designed and prototyped. Measured results indicate that the fabricated circuit can deliver a drain efficiency of 68.7/73.5% at saturation (43/42 dBm), and 56.9/48.1% at 10 dB-OBO at the frequency of 1.5/3.2GHz.

This paper proposes a new method to design compact and high-efficiency Class-F GaN microwave monolithic integrated circuit (MMIC) based power amplifiers (PAs). Closed-form design equations are derived to synthesize a multi-function bias branch sub-network (BBSN) and a harmonic-isolation matching branch sub-network (MBSN), which together form a network that is capable to satisfy the Class-F load condition from fundamental up to the $4^{th}$ harmonic frequency. These equations further assist in analyzing the impact of the finite inductor quality factor on the passive efficiency of the proposed network, yielding design choices that offer both reduced chip size and passive loss. For validation, the proposed method is applied to design a C-band high-efficiency PA in a commercial 0.25 $\mu {\mathrm{ m}}$ GaN-on-SiC HEMT process. Measurements under pulsed continuous-wave stimulation reveal, the proposed PA is capable of providing saturation output power of 38.5-39.1 dBm and excellent power-added efficiency (PAE) of 61%-70% over 5.3-5.9 GHz with a chip size of $1.5\times2.2$ mm2. Moreover, when excited by a 100 MHz 256-QAM signal, the amplifier can offer an average PAE of 33.1-38.2%, adjacent channel power ratio (ACPR) of $ < -35$ dBc, error vector magnitude (EVM) of 2.7-3.7%, without applying any digital pre-distortion (DPD).