A new type of backward coupling is observed between two parallel microstrip transmission lines on a slot Split-Ring Resonators (SSRRs) defected ground plane, even though the lines are separated with a large gap spacing. This enhanced coupling is achieved at a fixed desired frequency on only one channel and the coupling at other frequencies is done on another channel. The design of novel types couplers with relaxed gap spacing and possible applications for diplexers and transponders can be considered for the future. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 138–141, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21287