A Compact 923 MHz Monopole Antenna for LoRaWAN IoT Applications

This paper presents design and measurement verification of a compact monopole antenna with 923 MHz operating frequency for LoRaWAN Internet of Things (IoT) applications. The size of the proposed antenna is 13.11 × 22.95 mm2 which is extremely small compared to the wavelength at the operating frequency. The substrate material is FR-4 with a nominal relative dielectric constant of εr=4.3, loss tangent of tanδ=0.2 and a thickness of 1.6 mm. Miniaturization of the proposed antenna was achieved by using a short stub similar to the case with an inverted-F antenna combined with a folded monopole radiator. The measurement results of the proposed antenna show an impedance matching bandwidth of 4.5 MHz and a peak gain of -11.86 dBi with an omnidirectional radiation pattern. The low gain is typical for an electrically small antenna of this size according to the physical gain limit. Due to its extremely compact size, the proposed antenna is a good candidate for small IoT devices which can easily be integrated to physical objects in everyday life.