AbstractMost conventional transmission line filters are commensurate structures, with all elements that contribute to the filter performance of equal length. In this article, a structure is described that makes use of a series of elements that vary in length and spacing according to a logarithmic function; this results in a series of transmission zeros at real frequencies. It is shown that excellent filtering performance can be obtained from a relatively simple construction. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2418–2420, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24652