A class-F high efficiency GaN power amplifier (PA) for dual band operation at 2.14 GHz and 2.35 GHz is proposed. A novel dual band harmonic-rejection load network, which controls the terminating impedances of the second and third harmonics, and contributes greatly to efficiency improvement of PA, is described. In addition, a matching network which guarantees the high efficiency and gain of PA for the desired dual bands is designed. The proposed load network has the harmonic rejection of more than 24 dB which is sufficient for rejecting harmonics, and an insertion loss of less than 0.11 dB. The dual band matching network for the maximum output power results in the measured highest output power for each operating frequency. The fabricated class-F GaN PA has 43 dBm-65.4% and 43 dBm-63.9% of output power - efficiency at the desired dual frequencies.

An unequal Wilkinson power divider with adjustable power dividing ratio is proposed. The proposed power divider consists of rectangular defected ground structure (DGS), isolated island in DGS, and varactor diodes. The impedance of the microstrip line greatly increases due to the DGS, and varies because of the varying capacitance of diodes. The measured unequal dividing ratios vary from 1.97-13.4 and 2.25-10.6 when 2- and 4-diodes are adopted.

A design of dual band amplifier using composite right/left handed (CRLH) transmission line structure is described. First, two single-band matching networks are designed for two frequencies, and they are synthesized into one dual band matching network. It is shown that CRLH transmission lines with arbitrary dual frequencies and dual electrical lengths can be designed. The CRLH transmission line section for the dual band matching network is implemented by lumped inductors and capacitors as the left handed (LH) section, and normal transmission line elements as the right handed (RH) section. As an example, a dual band amplifier for 1800 MHz and 2300 MHz is designed and measured. The simulated and measured performances well verify the proposed design by showing good matching and gain responses at the desired frequencies.