Cylindrical Coplanar Waveguide Transition Circuit for Microwave Connections on Curved Surfaces

External connections are critical in microwave circuits, and designing impedance-matched coaxial transitions is a key challenge. While planar circuit transitions are wellstudied, limited attention has been given to transitions for curved surfaces, such as vials and test tubes commonly encountered in chemical and biomedical laboratories. With the growing demand for accurate in-situ measurements in these applications, addressing this gap has become increasingly important. This work introduces a novel transition from coaxial to coplanar waveguide (CPW) mode on a cylindrical surface, specifically designed for use with curved containers like vials. The proposed transition achieves a minimum return loss of 12 dB within the DC- 10 GHz band and maintains an insertion loss below 1 dB up to 6 GHz. Fabricated on a semi-flexible substrate, the design is well-suited for biomedical sensing and in-situ measurements of cylindrical samples.