Design Of C-band Internally-matched High-efficiency GaN Power Amplifier

Microwave power amplifiers (PAs) have met wide applications in the fields like radars, wireless communication base stations, satellites, aircrafts and aerospaceplanes. However, given the limitations of their own characteristics, the first and the second generation semiconductors are not qualified for these purposes. Due to the capabilities of radiation hard, high breakdown voltage, high power density and high electron mobility, gallium nitride (GaN) high-electron-mobility-transistor (HEMT) is the most promising candidate for microwave power applications. With the increase of power density, the area of the active region of GaN HEMT is greatly reduced, making the package size become smaller. However, miniaturization brings the heat problem at the same time. It is very important to improve the efficiency of microwave PAs not only to reduce the power dissipation, to lower the thermostat and to ensure the microwave performance, but also to extend the life time of batteries and devices.Based on the GaN HEMTs produced at Xidian University, a C-band internally-matched high-efficiency power amplifier is designed and manufactured.2nd-harmonic tuning sections are added to the matching network circuits for realizing both high output power and high efficiency at the same time. In the frequency range from 5.2GHz to 5.8GHz, the PA demonstrates a maximum output power of 163W and a power-added-efficiency (PAE) of 68.4% under a pulsed condition.The processing of GaN HEMT is introduced in this paper. The direct-current (DC) and radio-frequency (RF) characteristics of the GaN HEMT are measured by Agilent B1500A and microwave-probe system, respectively. The basic working principle of load-pull system is also introduced because it is indispensable for microwave circuit design. By comparing the advantages and disadvantages of different types of PAs, the PA represented in this paper is finally chosen to work as class-AB PA. The 2nd-harmonic tuning circuits are added to the matching network for suppressing the 2nd-harmonic component as well, thus obtaining higher efficiency.The design of C-band internally-matched GaN high-efficiency power amplifier is based on the improved EEHEMT large signal model. In order to obtain higher output power, the PA contains two parallel bound 12mm GaN HEMTs working as its active region. A Wilkinson power divider and a combiner are introduced to the circuits to separate the signals transformed by the PA into four ways. Through this way, the phase imbalance caused by the great gate width gets reduced. Both optimum efficiency impedances at fundamental frequency and 2nd-harmonic frequency are obtained by load-pull and source-pull simulation measurements using advanced design system (ADS) software. Fundamental impedances are then matched from the measured optimum fundamental impedances to 50Ω by the matching network circuits. On the other hand, by using of 2nd-harmonic tuning sections, the 2nd-harmonic component is suppressed to reduce its impact on the output waveform and to increase the PA’s linearity, and finally, to improve the efficiency. The schematic diagram of the PA is completed before drawing its layout, and then the manufacture of the modules made on ceramic substrates are achieved.Using internally-matched technology, the PA is actually made after the design work is done. First of all, HEMTs and circuit modules are sintered in the tube and bonded by bonding gold wire. An RF testing fixture working in the target frequency range with great RF performance is also designed and made in this paper. According to the very first testing parameters obtained from the PA, the matching network circuits are adjusted, demonstrating a good performance under small signal condition from 5.2GHz to 5.5GHz. At last, the RF power parameters such as output power, PAE and gain of the PA are tested under continuous wave and pulsed condition, respectively. According to the results, the C-band internally-matched GaN high-efficiency PA showed in this paper obtains a great performance in the working frequency range.