AbstractConventional techniques for designing waveguide‐to‐finline taper transitions are based on the design of a suitable impedance transformation profile used for pure TEM lines. Change of finline/slotline gap not only causes change in impedance but also correspondingly change in propagation constant. Thus the existing analysis, used for purely TEM lines, is inadequate in dealing with finline tapers. Analysis has also been carried out by varying the propagation constant using closed‐form expressions. Comparison of various taper profiles has been presented in this paper. Further in the present work, the width of the finline contour itself has been varied according to the function profiles as exponential, parabolic, cosine, and cosine squared forming the tapers. Broadband tapered transition from rectangular waveguide to offset slot asymmetric finline has been realized by gradually increasing the slot width using exponential taper profile. The designed asymmetric finline taper (two transition with one lambda spacing) using impedance variation with width exponential profile showed a very good result of 0.15–0.25 dB in the entire Ka‐band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2254–2257, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22688