We propose new empirical expressions for the characteristic impedance of a microstrip‐like interconnect line in presence of ground plane aperture. The existing characteristic impedance expressions are modified so as to include the effect of the ground plane aperture. The variation in the characteristic impedance vis‐à‐vis the aperture size is established. The proposed expressions are general and valid for a range of dielectric materials concerning MICs, RFICs, and PCBs. The results are validated by measurements performed on a vector network analyzer.