The Uhf Broadband Power Amplifier Research And Design

With the development of wireless communication technology, the demand for high capacity and high quality communications is improved continuously. In order to meet the needs of people, wireless communications must possess the characteristics of large data capacity, fast transmission rate and low bit error rate. Consequently, broadband data communications come into being. The research on broadband high-power amplifier is vital to the development of broadband communication technologies.A broadband high power amplifier is proposed and fabricated in this thesis. The output power can reach to 250 W within the band of Ultra High Frequency (UHF). It has not only the characteristics of broad frequency band and high power capacity, but also small size and high linearity, which make it suitable for broadband communication systems.Firstly, an overview of power amplifiers is introduced, and a brief description of the design specifications, classification and various linearization techniques of power amplifiers are given, The broadband matching theory and technology are highlighted at last.Based on the design specifications and the use of broadband matching theory and linear technology, a broadband linear power amplifier is designed. Firstly, the overall design scheme of the power amplifier is formulated according to the specifications. Secondly, some methods have been taken to resolve the problems encountered in the amplifier design. For example, the transmission line theory, lumped components and Balun technologies have been used to improve broadband matching performance. Amplitude equalization technique is used to flatten the gain. The linearization is achieved by using negative feedback technology and power back off technology. In the overall layout, the circuits with different functions are separated to reduce electromagnetic interference. At last, these technologies are used for the main circuit design and automatic level control (ALC) circuit design, respectively, while temperature control circuit and the detector circuit are used to realize a real-time monitoring of the power amplifier.The designed power amplifier is fabricated and measured. It is shown from the measurements that the VSWRs of the power amplifier is less than 1.2 at the input port , respectively, within the required frequency range. Also, a gain greater than 68 dB, second harmonic less than-42 dBc and third-order intermodulation less than -25 dBc have been obtained. Furthermore, an output power in excess of 54 dBm and power added efficiency of 36.1% have been achieved. Moreover, good thermal stability has been realized. In a word, all the specifications have been achieved successfully.