Another circuit construction commonly used for higher-frequency applications, which can be much more impacted by final finishes, is GCPW. This structure has two copper layers, and the bottom layer is the ground plane.
The GCPW circuit will be more impacted by a lossy plated finish than will the microstrip circuit because the final finish is in the coupled areas, and four layers of the finish are used by the circuit.
The results for the GCPW circuits shown in Figure 6b have a difference in insertion loss of about 1.2dB/in.
Electric field representation for a grounded coplanar waveguide (GCPW) circuit.
This article presents an effort to achieve an acceptable SOLR calibration on GCPW lines using the WinCal software.
 The four standards are GCPW lines fabricated on an FR-4 substrate with an effective dielectric constant of 2.57 and a characteristic impedance of 92 [omega].
The measurement results show that a good SOLR calibration using GCPW lines is feasible.