Near‐field sensor based on substrate integrated waveguide microstrip cavity resonator with a circular aperture

Abstract A near‐field planar sensor fabricated from a substrate integrated waveguide (SIW) cavity resonator is presented. The SIW cavity resonator is a modification of a rectangular microstrip antenna. The rectangular microstrip antenna radiates from two radiating edges that produce far‐field radiation, which is undesired for near‐field sensing. To suppress the radiation from the edges, the microstrip antenna is modified to have conducting vias that short all four edges of the patch to the ground plane. A circular hole is placed on the patch surface in the middle of the patch to form a sensing aperture. The field is thus confined inside the cavity with leakage only allowed through a small aperture, which is used for sensing surrounding objects in the vicinity of the aperture. This cavity resonator operates in the TM21 mode of the SIW cavity. Full‐wave simulations are performed and the results are consistent with the theoretical analysis as well as CAD formulas that are derived. The performance of the sensor as a near‐field sensing device and as a near‐field imager is explored.