A design method for microstrip directional couplers loaded with shunt inductors for directivity enhancement

Seungku Lee, Yongshik Lee

Research output: Contribution to journalArticlepeer-review

43 Citations (Scopus)


An accurate design method is proposed for directivity enhancement of microstrip directional couplers loaded with shunt inductors. The parasitic effects of junction discontinuities in various parts of such microstrip directional couplers have critical effects especially on the directivity, and therefore they must be taken into account. Without proper modeling of these parasitic effects, directivity enhancement becomes extremely difficult especially for weak coupling levels. The demonstrated method of analysis can be applied to obtain exact designs of all previous microstrip directional couplers that are loaded symmetrically with series and/or shunt reactance for directivity enhancement, regardless of the coupling levels. Based on the proposed method, a 20-dB microstrip directional coupler is designed at 2.4 GHz. A maximum directivity of 56 dB has been measured, which is an improvement of 48 dB over a conventional microstrip directional coupler. A 16.3% bandwidth at 2.4 GHz has been measured in which the directivity remains above 20 dB, while the maximum variation in the coupling level is 0.5 dB. This is the first work to demonstrate directivity of more than 50 dB for a 20-dB microstrip directional coupler.

Original languageEnglish
Article number5430893
Pages (from-to)994-1002
Number of pages9
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number4
Publication statusPublished - 2010 Apr

Bibliographical note

Funding Information:
Manuscript received February 24, 2009; revised December 04, 2009. First published March 15, 2010; current version published April 14, 2010. This work was supported by the Low Observable Technology Research Center and the Defence Nano Technology Application Center Programs of the Defense Acquisition Program Administration and the Agency for Defense Development of Korea under Contract UD080040GD and Contract UD090088JD.

All Science Journal Classification (ASJC) codes

  • Radiation
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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