A Fixed-Frequency Angular Displacement Sensor Based on Dielectric-Loaded Metal Strip Resonator

A fixed-frequency angular displacement sensor using a dielectric-loaded metal strip resonator is proposed. The dielectric body on which the strip resonator is attached is a cylinder having a high dielectric constant (e_r ≫ 1). The resulting resonator operates at the half-wave resonant frequency of the quasi-TEM mode of the loaded strip, which is much lower than the nominal resonant frequency of the strip. To enable angle sensing, the resonator is placed symmetrically between two 50 Ω, open-ended microstrip lines, so that the magnitude of the transmission coefficient(|S₂₁|) between the lines varies with the strip angle, i.e., 0° ≤ θ ≤ 90°. Also, this configuration ensures constant resonant frequency operation for all angles. Simulations show that although the |S₂₁| versus angle curve varies exponentially in the range of 0° ≤ θ ≤ 90°, the corresponding coupling coefficient varies quasi-linearly in 10° ≤ θ ≤ 80°. A laboratory prototype for ~ 2.4 GHz resonant peak is fabricated and the simulation results are verified through prototype measurement. The advantages of the proposed sensor are that it is compact, has a simple design, and operates at a fixed frequency, enabling a low-cost, robust angular sensor.