Design Of High-efficiency RF Power Amplifier

RF power amplifier is a key part of all kinds of wireless transmitter and radar systems, which largely increases the output power of the transmitter. The RF power amplifier with high efficiency can decrease the proportion that the power supply transforms power into heat, which can enhance the stability of the systems, reduce the area of the heat sink and prolong the life time of the batteries. Therefore, it is an important research field for RF power amplifier design to improve the efficiency of the RF power amplifier.Firstly, the design theory of class-E RF amplifier is introduced. Secondly, the low-pass impedance transforming network, the low-pass filter based on transformed radial stubs with ultra-wide stopband and the low-pass filter using stepped impedance hairpin units are discussed. The class-E RF power amplifier with the center frequency of 1.8 GHz using the transistor MRF6S27015 N is designed. Moreover, a class-E RF power amplifier based on the CGH40025 transistor operating at 1.6GHz is also designed. The output impedances of the transistors are obtained by using load-pull technique. The output network of the PA with 1.8GHz center operating frequency consists of a matching network and a low-pass filter with ultra-wide stopband based on transformed radial stub. The simulation results show that the power added efficiency is about 62.1%, the gain is about 12.3 dB and the output power is about 36.3dBm(4.3W) at 1.8GHz with 24 dBm input power. The PA is fabricated on the substrate with dielectric constant of 2.65 and height of 1mm. The measured results of the PA show that the power added efficiency is about 48.7%, the gain is about 11.2dB and the output power is about 35.2dBm(3.3W) at 1.8GHz with the input power of 24 dBm.The output network of the PA with 1.6GHz center operating frequency consists of a matching network and a low-pass filter based on the stepped impedance hairpin unit. The simulation results show that the power added efficiency of the power amplifier is about 80%, the gain is about 12.2dB and the output power is about 43.2dBm(21W) when the PA is operating at center frequency with 31 dBm input power. As discussed above, the class-E RF power amplifier can be realized through using the output matching network, which contains a low pass filter structure.