In this article, a novel method to improve the rejection of edge coupled filters by perturbing the coupled line sections by a length, δ, is introduced. This gives controls over the null position between the fundamental and 1st harmonic of the filter which results in a steeper rejection slope by shifting this null closer to the centre frequency. A 4th order 5 GHz band‐pass filter is designed and tested. Measured results show an improvement of about 9 dB at 6 GHz. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 680–683, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23176