Design of Planar Wideband Balun Model

Abstract

In order to meet the practical requirements of the balun structure while improving the output balance and isolation, an improved planar broadband balun model was designed based on Marchand balun. Aiming at the situation that the phase transition speed of the two output terminals is not synchronized due to the input transient transmission of the microstrip line, the method of compensating the microstrip line by loading the ground short-circuit ends of the two couplers is used to adjust the phase speed to synchronization and thereby improve the output balance. At the same time, a single-layer planar structure is used to reduce the vol-ume of the balun structure, and isolation circuits are introduced at the input and output ends to optimize the isolation. Simulation verification based on the model showed that the minimum isolation at the working frequency of 2.969GHz-3.702GHz was reduced to -24.53dB, and the phase imbalance at the output fluctuated between+0.32 °and -0.99 °, and the amplitude unbal-ance degree does not exceed 0.08db. The balance does not exceed -0.08dB. Both output bal-ance and isolation have been significantly improved.