Research On Doherty Power Amplifier With Ku Band Based On GaN HEMT

A Ku band Doherty power amplifier is researched in this paper which will be applied for satellitecommunication. The power that power amplifier consumes is a large proportion in the entiresatellite communication system and power amplifier is a nonlinear circuit that works under largesignal. So, increasing the efficiency and improving the linearity is an eternal subject to the designersof power amplifier. Doherty power amplifier can get high linearity by backing off power. Butduring backing off power, the efficiency of Doherty power amplifier is not significantly reduced, soDoherty power amplifier can ensure linearity while achieving a high efficiency.Firstly, the methods of the design of Doherty power amplifier, frequency broadband of satellitecommunication and gallium nitride, one of the third generation semiconductor materials areinvestigated and surveyed, and then the status and development trend of Doherty power amplifier athome and abroad is summarized. Then, the work status and main performance indexes of poweramplifier are introduced. The active device of the design is0.25mGaN HEMT from TriquintCorporation and it is a discrete transistor. Parameter extraction of an equivalent circuit model forthe transistor is carried out and loadpull is simulated based on the created model to get the optimumload impedance. By comparing the optimum load impedance tested that the datasheet of thetransistor offers with the optimum load impedance simulated, a good consistency is found to verifythe accuracy of the created transistor model. Then the bonding wires that connect the pads of thetransistor and microstrip lines are electromagnetic field simulated and optimized using HFSSsoftware and then accurate simulation data of the passive component model of bonding wires andthe microstrip lines that connect bonding wires are achieved. Based on the simulation data of thepassive component model, it is convenient to design accurate and stable matching circuits followedup.Based on the above, a Doherty power amplifier and a balanced power amplifier based on GaNHEMT are designed. The working frequency range of two power amplifiers is both14to14.5GHz.Then the simulated results of Doherty power amplifier and balanced power amplifier are comparedand analyzed.The14-14.5GHz broadband Doherty power amplifier is mainly designed using ADS softwareand HFSS software in this paper and it is two cascaded: one is drive stage and the other is powerstage. The structure of the power stage is Doherty. By simulating and optimizing schematic andlayout, the gain of small signal of14-14.5GHz broadband Doherty power amplifier is higher than19dB, VSWR of input and output are both smaller than1.3. Working on the large signal, the output power is more than12W, and power gain is bigger than15dB, and PAE is high than45%. Whenbacking off6dB of output power, the power added efficiency (PAE) can still achieve38%. Thebalanced power amplifier with the same working frequency broadband working on the large signalcan get the PAE of42%when it is saturated, but when the saturated output power is backed off6dB,PAE is reduced to25.5%. Working in Ku band that has very high frequency, the PAE of thedesigned Doherty power amplifier is12.5%higher than that of the balanced power amplifier and itshows that the designed Doherty power has a good performance. The results of the simulation showthat the designed Doherty power amplifier has achieved the expected specifications.During processing and testing, firstly, main power amplifier in the power stage of the designedDoherty power amplifier is processed.Then a circuit is designed that used for power-on sequenceprotection using Altium Designer software. When power amplifier is tested, the transistor can beprotected effectively with the protection circuit.Then, based on the size of main power amplifier andensuring not generating self-resonant frequency, a shied case used to test power amplifier, shiedelectromagnetic and dissipate heat is designed using AutoCAD software. Then the main poweramplifier module is tested and the analyses of the tested and simulated results are given. Thedesigned Doherty power amplifier can be adjusted based on the analysis and summary and then agood performance of the subsequently processed Doherty power amplifier can be ensured.