The main requirements for RF rotary couplers employed in contactless resonant SAW torque sensors have been formulated in the paper. They are: (a) flat frequency response, (b) small angular variation of the measured resonant frequency, (c) small angular variation of the insertion loss, and (d) insensitivity to manufacturing tolerances and contaminations. A theoretical analysis has been performed to establish influence of the coupler on the measured SAW natural oscillations. As a result the frequency of the natural oscillations, their length and amplitude have been found as functions of the coupler's output impedance and insertion loss. The results are applicable not only to RF rotary couplers but also to any combination of sensor and interrogation antennas including those positioned in the near field of each other.
展开▼
