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Analysis and design of a branch‐line balun with high‐isolation wideband characteristics
Author(s) -
Kim Phirun,
Chaudhary Girdhari,
Jeong Yongchae
Publication year - 2015
Publication title -
microwave and optical technology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 76
eISSN - 1098-2760
pISSN - 0895-2477
DOI - 10.1002/mop.29065
Subject(s) - balun , wideband , return loss , electrical engineering , center frequency , stub (electronics) , bandwidth (computing) , microwave , transmission line , electric power transmission , standing wave ratio , impedance matching , reflection coefficient , resistor , engineering , electrical impedance , electronic engineering , physics , telecommunications , antenna (radio) , voltage , band pass filter , microstrip antenna
ABSTRACT This article presents a design of wideband balun with high isolation using a branch‐line structure. Theoretical analysis of the proposed balun shows that the reflection coefficient characteristics with two transmission poles can be obtained by controlling the characteristic impedances of transmission lines (Z t , Z 1 , and Z 2 ). The high isolation can be obtained by adding a shunt coupled‐line short stub and resistor (R) between the output ports. The proposed balun was designed at the center frequency (f 0 ) of 2.6 GHz for a current‐mode class‐S amplifier application. The measured results were in good agreement with the simulations, showing that power division ratios were 3.09 dB and 3.14 dB, whereas the return loss was 21.39 dB at the f 0 and higher than 20 dB over a bandwidth of 0.98 GHz (1.98–2.96 GHz). The isolation between output ports was higher than 18 dB for the bandwidth of 0.75 GHz (2.21–2.96 GHz). The measured phase difference between the output ports was 180° ± 9° over a frequency range of 2.2–2.98 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1228–1234, 2015