Flexible Single-Layer Low-Cost Coplanar Waveguide Slot Inverted-F Antenna for Internet of Things Applications

This work presents the design, fabrication, and characterization of a flexible planar slot inverted-F antenna (PIFA) based on coplanar waveguide technology (CPW), operating at 2.4 GHz and intended for Internet of Things (IoT) applications. The proposed antenna features a slot-based surrounding ground conductor, enabling its use in antenna array configurations without interconnection wires. Two low-cost and low-profile fabrication alternatives are assessed: (i) robot-assisted additive manufacturing using inkjet technology with conductive silver-based ink; and (ii) metallization through conductive spray sputtering on laser-patterned masks. The impact of conductivity on the antenna performance metrics is examined, revealing that increasing the amount of conductive paint sputtered in prototypes fabricated by method (ii) enhances the conductivity but decreases mechanical flexibility. The optimised design achieves a bandwidth of ∼150 MHz and a gain of 2.9 dBi and 2.6 dBi for antennas fabricated using methods (i) and (ii), respectively. The influence of the bending angle along the x and y axes is also evaluated, demonstrating a negligible degradation in S-parameter measurements. Mechanical stress tests involving 50 and 100 bending cycles were conducted, revealing minimal deterioration. Radiation patterns are characterized using the three-antenna method in an anechoic chamber, confirming similar performance for both (i) and (ii) manufacturing methods. This comprehensive study paves the way for future low-cost antennas aimed at flexible IoT applications.