We present a compact and broadband balun based on the concept of a synthetic left-handed transmission line and right-handed transmission line. The compact balun uses lumped, discrete LC elements only to reduce the circuit size dramatically. For the frequency range of 0.6-1.2 GHz, this circuit maintains 180 6 9.5 phase difference at the outputs, whereas the maximum insertion loss is À1.78 dB, and the minimum return loss is À10.2 dB at all three ports, yet the circuit size is merely 12 Â 8 mm 2 . As far as we know, this is the smallest broadband balun reported in the literature, and the size can be further reduced, if the circuit is made with a monolithic microwave integrated circuit technology.ABSTRACT: This article describes the design, realization, and characterization of a set of hybrid medium-power RF power amplifiers, based on a commercial packaged GaN HEMT and developed through a low-cost microstrip process. Two different design solutions suitable for wireless applications are presented: the first, intended for a constant envelope modulation (with reference to the GSM standard) is a Class F amplifier exhibiting at 900 MHz an efficiency of 72% with an output power of 37.5 dBm; the second, optimized for nonconstant envelope signals with high dynamics (with reference to the UMTS WCDMA standard) is a Doherty amplifier showing, at 2.14 GHz, an efficiency higher than 40% at 6 dB of output power back-off with a maximum output power of 40 dBm.