Design and characterization of multilayer spiral transmission-line baluns

Yeong J. Yoon, Yicheng Lu

Research output: Contribution to journalArticlepeer-review

76 Scopus citations


We discuss the design of coupled spiral transmissionline baluns modeled after the Marchand type. The balun structure consists of a pair of coupled spiral conductors vertically offset across intervening polyimide layers. The baluns are fabricated on various substrates (glass and high- and low-resistivity silicon). The characteristics such as return loss, insertion loss, and output signal imbalance are measured. The center frequencies of 3-dB bandwidths (BW's), primarily determined by their conductor lengths, range from 1.2 to 3.5 GHz. The 3-dB BW normalized by the center frequency is ~1.48 in all cases. We observe an optimum BW for better performance. Return losses at the center frequencies range from 13 to 18 dB. Amplitude imbalance distributes in the range of 0.3-1.0 dB, depending on the sizes of devices and substrates. The minimum insertion loss is 0.55 dB for the balun on a glass substrate with 100-jum-wide conductors. The devices fabricated on glass and high resistivity (>4000 £7 cm) silicon show remarkably similar behaviors despite the large difference in dielectric constant. This technique is applicable to monolithic microwave integrated circuits.

Original languageEnglish (US)
Pages (from-to)1841-1847
Number of pages7
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number9 PART 2
StatePublished - 1999

All Science Journal Classification (ASJC) codes

  • Radiation
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


  • Balun
  • MMIC
  • Multilayer
  • Passive devices
  • Transmission line


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