A compact electric field probe sensor incorporating two different electro-optic materials of $LiNbO_3$ and GaAs was proposed and fabricated, and it was used to measure the strength of the horizontal and vertical fields generated by a microstrip ring-resonator filter. The sensitivities of the sensors in $LiNbO_3$ and GaAs were $9.315{mu}V/sqrt{Hz}$ and ${sim}49.346{mu}V/sqrt{Hz}$ respectively, and their signal to noise ratios were approximately ${sim}50;dB$ and ${sim}40;dB$ respectively. And the operating frequency range was up to ${sim}1.2;GHz$. The electric field profile for the test circuit was scanned and found to be in good agreement with that obtained by using the HFSS simulation.