This paper describes the performance improvement of power amplifiers by defected ground structure (DGS). Due to the excellent capability of harmonic rejection and tuning, DGS plays a great role in improving the major nonlinear behaviors of power amplifier such as output power, harmonics, power added efficiency (PAE), and the ratio between the carrier and the third order intermodulation distortion (C/IMD3). In order to verify the improvement of performances by DGS, measured data for a power amplifier, which adopts a 30 Watts LDMOS device for the operation at 2.1-2.2 GHz, are illustrated under several operating bias currents for two cases, i.e., with and without DGS attached. The principle of the improvement is described by the simple Volterra nonlinear transfer functions with the consideration of different operating classes. The obtained improvement of the 30 Watts power amplifier, under 400 mA of IdsQ as an example, includes the reduction in the second and third harmonics by 17 dB and 20 dB, and the increase in output power, PAE, and C/IMD3 by 1.3 Watts, 3.4%, and 4.7 dB, respectively.

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.