Article

New Isolation Circuits of Compact Impedance-Transforming 3-dB Baluns for Theoretically Perfect Isolation and Matching

Dept. of Electr. Eng., Univ. of California at Los Angeles, Los Angeles, CA, USA
IEEE Transactions on Microwave Theory and Techniques (Impact Factor: 2.23). 01/2011; DOI: 10.1109/TMTT.2010.2087348
Source: IEEE Xplore

ABSTRACT New isolation circuits and design equations of compact impedance-transforming 3-dB baluns are suggested for theoretically perfect isolation and perfect matching at all ports. Any balun consists of two impedance transformers, being 180° out of phase, and an isolation circuit. For compactness, the impedance transformers need to be reduced and the isolation circuits should depend on phase delay of the compact impedance transformers. The compact balun with -90° phase delay of the compact impedance transformer is called the compact II-type balun and the one with non -90° phase delay is called the constant voltage-standing-wave-ratio type transmission-line impedance transformer (CVT) balun. Three isolation circuits are derived for the compact II-type baluns and five for the CVT baluns. Using the isolation circuits derived, the two types of compact baluns are fabricated and measured at a design center frequency of 1.5 GHz. The measured results have good agreement with prediction, showing power divisions of -2.9 and -3.3 dB (- 2.8 and -3.25 dB ), phase difference between two output signals of 181.8°(178.5°) , matching performance of -21.8, -31.8, and -33.8 dB ( -24, -22, and - 28 dB), and isolation of better than 40 dB (27 dB) for the compact II-type (CVT) balun.

0 Bookmarks
 · 
70 Views
  • IEEE Transactions on Microwave Theory and Techniques 09/2011; 59(9):2370-2371. · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: New symmetric equivalent circuits are suggested for 90° and 270° transmission-line sections, with which compact coupled-line ring and branch-line hybrids can be designed and fabricated. For this purpose, firstly stepped-impedance transmission-line (SITL) sections, being equivalent to a uniform transmission-line section with arbitrary electrical lengths, are synthesized, and design formulas for the SITL sections are derived. Secondly, three types of equivalent circuits are introduced by combining the SITL sections with coupled-line Π-, modified Π-, or T-type, and are called stepped-impedance coupled-line Π-type (SCΠ ), stepped-impedance modified T-type (SMT), and stepped-impedance modified Π-type (SMΠ). The SCΠs are for 270° transmission-line sections, while both SMTs and SMΠs are for 90° transmission-line sections. Based on the suggested equivalent circuits, compact coupled-line ring and branch-line hybrids designed at 1 GHz are fabricated, and the measured bandwidth of the ring hybrid is 50% with 15-dB return loss. The measured results may be considered as excellent, reflecting their total transmission-line lengths of 183° and 111° for the ring and branch-line hybrids, respectively.
    IEEE Transactions on Microwave Theory and Techniques 03/2013; 61(3):1067-1078. · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: For size reduction and design flexibility of impedance transformers, two modified asymmetric impedance transformers are suggested. They each consist of one open stub and two different transmission-line sections and are named a modified constant conductance-type transmission-line impedance transformer (MCCT) and a modified constant voltage-standing-wave-ratio (VSWR)-type transmission-line impedance transformer (MCVT), depending on where the open stub is located. As their applications, impedance-transforming MCCT- and MCVT-three-port 3-dB power dividers (MCCT- and MCVT-PDs) are presented, and it is found that the isolation circuits should be composed of not only resistance but also capacitance. For high-power applications, MCCT and MCVT Gysel-type PDs are also suggested, and four isolation circuits are developed systematically based on the isolation impedances of the MCCT- and MCVT-PDs. The isolation circuits of the Gysel-type PDs are comprised of three transmission-line sections, shunt resistances connected to ground, and series capacitances/shunt inductances. One MCCT-PD and one MCVT Gysel-type PD are verified by measurements. The measured results show good agreement with the prediction, giving power divisions of ${-}$3.08 dB, return losses better than 23.8 dB, and isolation of 24.07 dB at 1 GHz for the MCCT-PD and power divisions of about ${-}$3.42 and ${-}$3.5 dB, return losses better than 21 dB, and isolation of 28 dB at 2 GHz for the MCVT Gysel-type PD.
    IEEE Transactions on Microwave Theory and Techniques 01/2011; 59(12):3312-3321. · 2.23 Impact Factor