Research on Grounded Coplanar Waveguide for Calibration of Digital Real-time Oscilloscope Probe

In this paper, the grounded coplanar waveguide (GCPW) used for the calibration of high-bandwidth digital real-time oscilloscope probes is studied. First, according to the characteristic impedance formula of the grounded coplanar waveguide without via holes, the sizes of GCPW are adjusted so that the characteristic impedance is 50Ω. Moreover, the influence of via holes on the bandwidth of the GCPW is studied through simulation software, at the same time the sizes and position of the via holes are changed to increase the GCPW bandwidth to 50 GHz. The sizes of the GCPW with via holes is further changed to eliminate the effect of via holes on the characteristic impedance. The GCPW is made by machining on the basis of the simulation data, then its S-parameters are measured by the vector network analyzer. In the frequency range of DC-50GHz, S21 is greater than −2.2dB and S11 is less than −14dB. The research results show that the bandwidth and transmission characteristics of the GCPW can meet the requirements of calibration.