Design of balanced power amplifier with adopting new type of trans-directional microwave couplers

• Main Authors: Shih Tung Chou, 周世東
• Other Authors: Y. C. Chiang
• Format: Others
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/41883994131314161263

碩士 === 長庚大學 === 電子工程學系 === 100 === Conventional microwave balanced amplifier can increase its output power and provide very good impedance matching at its input and output ports. Thus, it is easy to connect with other circuits and eliminate the use of extra components to achieve the desired impedance matching. Since the traditional microwave amplifier is usually composed by branch line coupler and thus it need to be implemented with large circuit area. To improve this disadvantage, we propose a new feature of the balanced amplifier that uses the trans-directional microwave couples to realize the balanced amplifier in this thesis. This kind of balanced amplifier can provide several advantages as compared with conventional structure. First, it allows the amplifiers in the balances amplifiers to share the same DC bias circuitry and eliminate the need of DC blocking capacitors with placing the trans-directional couplers instead of the branch-line couplers in the conventional structure. Secondly, it will also reduce the required area for realizing a balanced amplifier. However, the proposed new structure still keep the same advantages of traditional balanced amplifier such as increased output power and input and output impedance matching function. For verifying the proposed circuit structure and design theory, we designed a balanced amplifier to operate at 2.4GHz for the commercial WLAN applications. It is a two stage design and constructed on the FR4 PCB circuit board with using some surface mount components and two bipolar transistors. This circuit has size 43mm6mm. The measurement of the prototype shows the maximum output power can reach 25.75dBm and input and output return loss all below 20dB within the frequency band of interest. The required power consumption is about 0.18W.