A 60-W L-Band Class-E/Fodd,2 LDMOS Power Amplifier Using Compact Multilayered Baluns

Abstract

Abstract – A Class-E/Fodd,2 power amplifier is reported that operates at 1.1 GHz, with an output power of 60 W and a power-added efficiency of 65%. Compact, low-loss impedance-transforming microstrip baluns are used in a push-pull configuration. The circuit board dimensions are only 3.5 cm × 5.0 cm. The amplifier uses a pair of Motorola 284 LDMOS transistors. The amplifier is intended for space-based phased-array radar T/R modules. Switching-mode amplifiers are promising candidates for UHF transmitters that require high efficiency, but only limited bandwidth and linearity. Recently Kee et al. reported a new class of switching power amplifiers – the Class-E/F amplifier [1]. Figure 1a shows the schematic of an E/Fodd,2 amplifier. This amplifier has zero-voltage switching like a Class-E amplifier, while terminating the odd harmonics and the 2nd harmonic like a Class-F-1 amplifier. The amplifier uses a pair of transistors, driven as switches 180 ° out of phase. A second-harmonic trap helps shape the current waveform. Figure 1b shows a photograph of the actual amplifier. The amplifier is built on a Duroid substrate with a dielectric constant of 2.2. Push-pull amplifiers need a balun at the input and output when amplifier is connected to coaxial cables. However, at frequencies in the 1-GHz range, traditional microwave baluns, such as hybrid rings, are larger than we would like. Broadside coupling is used for our input and output baluns, with a pair of stacked microstrip lines separated by a Duroid dielectric layer 180 µm thick. The dimensions of the baluns are optimized with the