Truncated Near-Field Microwave Microscope With High Quality Factor in Wide Frequency Range for Permittivity Measurement

The manuscript proposes a truncated near-field microwave microscope structure, which is composed of a re-entrant coaxial cavity and a coplanar waveguide probe with two-sided symmetrical grounding. The connection between the middle conductive strip of the probe and the inner conductor of the coaxial cavity is cut off to weaken the loss of cavity caused by the probe, thereby improving the quality factor of the proposed cavity. On the basis of ensuring that the coaxial cavity itself is free of higher order modes, the effects of two key parameters on the quality factor and sensitivity are simulated and analyzed by high-frequency structure simulator (HFSS), and the optimal parameter ranges are finally determined. The quality factor can reach a value in excess of 1568 within the frequency range of 0.8–7 GHz. Finally, the permittivities of the Rogers substrate and the glass fiber-reinforced plastic (FRP) are extracted based on the perturbation method.