Fractal-shaped microstrip coupled-line bandpass filters for suppression of second harmonic

Il Kwon Kim, Nickolas Kingsley, Matt Morton, Ramanan Bairavasubramanian, John Papapolymerou, Manos M. Tentzeris, Jong Gwan Yook

Research output: Contribution to journalArticlepeer-review

116 Citations (Scopus)


In this paper, microstrip coupled-line bandpass filters using a Koch fractal shape are proposed for the first time. These filters are fabricated on a liquid crystal polymer (LCP) substrate for K u-band. Conventional microstrip coupled-line filters are very popular for RF front ends because they can be fabricated easily. However, their large second harmonic causes the shape of the passband to be asymmetric in the upper band and it worsens the skirt properties. By proper design, the second harmonic of fractal filters can be significantly suppressed through the use of fractal shapes. In this paper, using LCP, the maximum harmonic suppression was almost 42 dB. This type of filter can be used to suppress the second harmonic without any additional devices and regardless of the substrate.

Original languageEnglish
Pages (from-to)2943-2947
Number of pages5
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number9
Publication statusPublished - 2005 Sep

Bibliographical note

Funding Information:
Manuscript received December 2, 2004. This work was supported in part by the International Research Internship Program of the Korea Science and Engineering Foundation and by the Georgia Electronic Design Center.

All Science Journal Classification (ASJC) codes

  • Radiation
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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