Novel Miniaturized Circularly Polarized Inverted-F Antenna With Planar Configuration

This letter proposes a novel miniaturized circularly polarized (CP) planar inverted-F antenna (PIFA) based on complementary sources. Different from the conventional 3-D CP antennas, a pair of planar complementary sources (electric-dipole/E-dipole and magnetic-dipole/M-dipole) are cleverly explored to realize CP radiation. To reduce size, a PIFA radiator and an L-shaped quarter-wavelength slot are integrated into a planar single-layer structure. Here, the PIFA radiator works as an E-dipole, and the L-shaped slot is considered an M-dipole, so two orthogonal components are obtained. Owing to the far-field characteristics of the complementary sources, a stable 90° phase difference is naturally obtained. Thus, a good CP wave is obtained. To validate the presented concept, a planar CP PIFA with a compact size of 0.17λ₀ ×0.58λ₀ (single-layer) is implemented at the 2.40 GHz WiFi band. The measured −10 dB impedance bandwidth and 3 dB axial ratio (AR) bandwidths are 2.34–2.56 GHz (9.0%) and 2.44–2.72 GHz (10.9%), respectively. Besides, this design shows good characteristics of CP coverage (Omnidirectional CP) and radiation efficiency (>85.5%). It is a good candidate for Internet of Things (IoT) applications.