Direct high frequency measurement method for small diameter coaxial cable

We are developing a high-quality flexible coaxial cable with a diameter of less than 1 mm. It is difficult to carry out precise measurement using the conventional coaxial connectors that are commercially available. Therefore, we have developed a high frequency measurement method for determining the characteristics of a small-diameter coaxial cable without exclusive connectors. In this method, a time domain reflectometry (TDR) measurement system and a microwave vector network analyzer (VNA) are used with a microwave probe station. The cables are molded using resin and cut vertically with a cutting tool. The surfaces of the cable edges are polished to obtain a good electrical contact. Microwave contact probes (SG or GS type) are used. We have precisely measured the characteristics of 0.8-mm-diameter coaxial cables. The impedance distribution and S parameters were successfully evaluated by TDR and VNA measurement respectively. The impedance distortion at the probe contact was negligible. The effects of the connection performance are discussed in detail.