Novel systems of an evanescent microwave probe (EWP) are disclosed, which enable measurements of physical properties of a sample with enhanced sensitivity and resolution, simultaneously. In one embodiment, new shielding features are added to the probe (which may be of either a sharpened tip or loop configuration) to reduce the effects of residual far field radiation, while maintaining the probe section that extends beyond the shielding aperture of the resonator. To further increase the sensitivity of the instrument, an automatic gain-controlled active feedback loop system may be added to the probe resonator to form a self-oscillator. This new active circuit feature significantly increases the effective Q of the resonator probe, enhancing the sensitivity of both the frequency and Q measurement.