Filtering Angular Displacement Sensor Based on Transversal Section With Parallel-Coupled-Line Path and U-Shaped Coupled Slotline

An ultra-wideband (UWB) bandpass-filtering microstrip circuit with an embedded in-band transmission zero (TZ) for co-integrated angular displacement RF sensing is reported. It is based on a two-layer structure that exploits a combination of a UWB transversal filtering section (TFS) with a parallel-coupled-line (PCL) path and a U-shaped slotline acting as the stator and a semi-circular slotline acting as the rotor. As the rotor consisting of a semi-circular slotline rotates, the degree of coupling between the slotline of the stator and the rotor is altered in a contactless fashion, thus varying the stator slotline effective lengths and, hence, the in-band TZ location and its rejection depth that enable to perform the rotation-RF-sensing task. The equivalent circuit model of the engineered dual-functionality UWB bandpass filtering/ angular displacement sensing RF device is provided, together with a numerical/parametric evaluation to study its performance. The sensing capability is analyzed for an example circuit built with a UWB bandpass filtering transfer function centered at 1.8 GHz with a fractional bandwidth of 110%. Furthermore, a proof-of-concept microstrip prototype with an angular rotation range of 90° is developed and tested to validate this approach experimentally. The average frequency sensitivity in terms of the variation of the in-band TZ location is 2.27 MHz/°, showing enhanced linearity and contactless operation as added merits compared with prior-art TFS-based rotational angle sensors.