Polarization Reconfigurable Air-Filled Substrate Integrated Waveguide Cavity-Backed Slot Antenna

Abstract

The Internet of Things requires highly efficient ultra-wideband antenna systems that yield high performance at low manufacturing cost. Therefore, a novel ultra-wideband circular air-filled substrate-integrated-waveguide (AFSIW) cavity-backed annular slot antenna is proposed that enables straightforward integration into general-purpose materials by means of standard manufacturing techniques. The cavity top plane, serving as antenna aperture, contains two concentric annular slots, both split into two by shorting tabs that create a virtual electric wall. This enables the generation of a TE11,slot even mode in both parts of each annular slot, giving rise to a conical radiation pattern. By exciting two such modes and judiciously positioning their resonance frequencies, all the unlicensed national information infrastructure (U-NII) [5.15-5.85] GHz radio bands are covered. The annular slot antenna is then made polarization reconfigurable through an innovative excitation of the slot modes by replacing the shorting tabs with four pairs of the PIN diodes. These dynamically switch between two orthogonal linear polarizations by changing the dc control current at the antenna RF port through an external bias tee. This simple, yet effective, bias network enables the integration of all polarization control electronics inside the antenna cavity to protect them from environmental effects. A low-cost antenna substrate was realized through standard additive manufacturing in a 3D-printed substrate, while a standard high-frequency laminate was used to implement the upper conducting plane containing the radiating elements and the polarization reconfiguration electronics. The antenna features an impedance bandwidth of 0.93 GHz, a front-to-back ratio of 14 dB, a total antenna efficiency higher than 95%, and 4.9 dBi gain for each polarization state.