Analysis and design of a branch-line balun with high-isolation wideband characteristics

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 (Zt, Z1, and Z2). 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 (f0) 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 f0 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

[1]  Yu-Chih Hsiao,et al.  A New Broadband Marchand Balun Using Slot-Coupled Microstrip Lines , 2010, IEEE Microwave and Wireless Components Letters.

[2]  Amin M. Abbosh,et al.  Planar ultra-wideband balun using coupled microstrip lines , 2013 .

[3]  Kyung-Whan Yeom,et al.  An Active IF Balun for a Doubly Balanced Resistive Mixer , 2009, IEEE Microwave and Wireless Components Letters.

[4]  Tatsuo Itoh,et al.  New Isolation Circuits of Compact Impedance-Transforming 3-dB Baluns for Theoretically Perfect Isolation and Matching , 2010, IEEE Transactions on Microwave Theory and Techniques.

[5]  Stuart Crozier,et al.  Wideband and compact quasi-Yagi antenna integrated with balun of microstrip to slotline transitions , 2013 .

[6]  Quan Xue,et al.  Miniaturised branch-line balun with bandwidth enhancement , 2007 .

[7]  Kian Sen Ang,et al.  A derivation of a class of 3-port baluns from symmetrical 4-port networks , 2002, 2002 IEEE MTT-S International Microwave Symposium Digest (Cat. No.02CH37278).

[8]  Hao Xin,et al.  A Tapped Stepped-Impedance Balun With Dual-Band Operations , 2008, IEEE Antennas and Wireless Propagation Letters.

[9]  Jong-Sik Lim,et al.  A size-reduced CPW balun using a "X"-crossing structure , 2005, 2005 European Microwave Conference.

[10]  Yi-Chyun Chiang,et al.  Design of a New Type Planar Balun by Using Trans-Directional Couplers , 2012, IEEE Transactions on Microwave Theory and Techniques.

[11]  Sangwook Nam,et al.  New Design Formulas for Impedance-Transforming 3-dB Marchand Baluns , 2011, IEEE Transactions on Microwave Theory and Techniques.

[12]  Yongchae Jeong,et al.  Wideband impedance transformer with out-of-band suppression characteristics , 2014 .

[13]  Byungje Lee,et al.  Stubbed Branch Line Balun , 2007, IEEE Microwave and Wireless Components Letters.

[14]  K. Blau,et al.  Reconstruction filters for switched-mode power amplifier systems , 2009, 2009 European Microwave Conference (EuMC).

[15]  Kian Sen Ang,et al.  Analysis and design of miniaturized lumped-distributed impedance-transforming baluns , 2003 .

[16]  I.D. Robertson,et al.  On miniaturization isolation network of an all-ports matched impedance-transforming Marchand Balun , 2003, IEEE Microwave and Wireless Components Letters.