Wideband circularly polarized printed antenna designed based on theory of characteristic modes

Today, the development of modern wireless communication systems demands wideband circularly polarized (CP) antennas capable of simultaneous multi-band operation within the compact footprint of telecommunication devices. Printed antennas are widely adopted for their low profile and ease of integration; their design remains challenging due to the difficulty of simultaneously achieving wide impedance bandwidth and stable CP, with most conventional approaches still relying on trial-and-error methods.

The theory of characteristic modes (TCM) offers a robust and efficient design framework that outperforms traditional techniques, which are often computationally intensive and time-consuming. Furthermore, the application of TCM provides deep physical insight into the underlying operating mechanisms of the antenna. This work employs TCM to guide the systematic design of a wideband printed antenna with CP.

Based on characteristic mode analysis, the proposed antenna achieves an impedance bandwidth of 2…4.54  GHz, with CP (axial ratio less 3 dB) maintained across 2.27…4.07 GHz. The maximum gain is 3.84 dBi at 2.8 GHz and remains above 3 dBi in the frequency range of 2.4…3.2 GHz. The antenna radiation pattern is bidirectional along the z-axis with a sufficiently wide beamwidth.

The antenna is well suited for diverse wireless applications, particularly 5G sub-6 GHz systems, and the TCM-driven design methodology provides a general framework applicable to the development of other advanced antenna structures. Its operating frequency range covers the 5G NR bands standardized by 3GPP. Furthermore, the proposed antenna is highly promising for hybrid terminals in NTN architectures and Direct-to-Cell/Device scenarios.