Circular Cavity Backed Water Drop Shaped Slot SIW Antenna

Abstract

The paper presents a planar circular cavity backed antenna (CBA) based on substrate integrated waveguide (SIW) technology. A water drop shaped slot is etched at the back of the circular SIW cavity which demonstrates a circular cavity backed slot antenna (CBSA-SIW). The water drop shaped slot antenna is designed within the usual smartwatches dimension. The application of the proposed antenna is in smartwatches but it could be extended to medical wristbands at 5 GHz. The complete surface of the antenna cavity is built using conducting material and the volume is filled with substrate material Rogers RO4003C having dielectric constant of 3.38. The overall cavity has a tube-shaped design and the complete volume is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pi\times 784\times 2.07$</tex> mm3. The radius and circular perimeter of the outermost edge of the antenna is about <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.87\lambda$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5.55\lambda$</tex> . This allows design to be significantly compact for smartwatch users. The proposed smartwatch antenna design is intended to be used within a free space environment. To achieve efficient and robust performance, the design is simulated as well as examined with an artificial software-based computer hand with real world muscle properties. The outcomes of the simulation result demonstrate that the antenna has an efficiency of more than 95% on a phantom body. To examine the antenna performance further, the microelectronic devices within smartwatch are modelled as a conducting block. The various resonance modes of the SIW cavity, surface current density, and electric field intensity of the slot antenna are examined and then dimensional parameters are optimized for high gain radiation. The design optimization is realized on a circular SIW metallic cavity while preserving the full mode SIW scheme. Further, to enhance the radiation property of the slot antenna an additional metallic via is placed within the vicinity of the antenna. It blocks the generation of higher order resonance modes at nearby frequencies and provides higher gain. The achieved impedance bandwidth and the peak antenna gain of the proposed design are 152 MHz (4.918-5.07 GHz) and 13.9 dBi in free space, respectively. The performance of the antenna does not differ from free space environmental conditions to real world scenarios. This demonstrates the proposed antenna is rigid and fit for on-body or off-body conditions.