A Wideband Microstrip Line-Based Balun Structure for High Power Amplifier Applications

This paper proposes a balun matching technique to achieving a high output power and wide bandwidth. The proposed structure includes microstrip transmission line-based even and odd mode-matching circuits. A three-port unipolar microstrip line is designed to transform the balanced load termination to 50 Ω unbalanced port impedance. The proposed network design is based on real symmetrical four port network with open ended transmission line is inserted between the middle of the structure. To improve the isolation, transmission coefficient parameter and match the 50 Ω termination, a resistive network is inserted between the two balanced ports. The proposed structure is simulated in Keysight Technologies Advanced Design System (ADS), fabrication is done by using 0.51 mm RT Duriod substrate alignments. To verify the design concept, first of all, a wideband microstrip matching technique is designed and characterized at the frequency of L5 band (1.17 GHz). Then a prototype of microstrip transmission line-based wideband balun matching circuit is designed and fabricated. Analytical design equations have been derived for the even mode as well as odd mode techniques which satisfied the results. The proposed balun could overcome power loss mechanism over traditional transmission line structures and can utilize for high power application.