A Dual-Band Dual-Circularly-Polarized Slot Antenna With Stable In-Band Gain and Reduced Frequency Ratio Under Triple Resonance

In this article, a dual-band dual-circularly polarized (CP) narrow slot antenna with stable in-band gain and reduced frequency ratio (FR) is proposed by resonating the
$0.5\lambda $
-,
${\it \lambda }$
-, and
$2{\it \lambda }$
-modes. For this purpose, two critical issues are significantly investigated and explored. The first effort is attempted to construct two pairs of orthogonal polarization with opposite rotation, i.e., (
${\it \lambda }$
- and
$0.5{\it \lambda }$
-modes) and (
$0.5{\it \lambda }$
- and
$2{\it \lambda }$
-modes), by properly reshaping the equivalent magnetic currents of the slot radiator. Another attempt is to reallocate these modes in proximity to each other in virtue of stub-loaded technique and ensure them to resonate in the designated sequence of
${\it \lambda }$
-,
$0.5{\it {\lambda }}$
-, and
$2{\it \lambda }$
-modes instead of the inherent sequence. With these improvements, the dual-CP performance can be successfully realized for our designed antenna. Finally, for experimental verification, a dual-band dual-CP slot antenna in virtue of the proposed design approach is implemented and tested. It proves that the left- and right-hand CP radiation patterns toward the
${z}$
-axis are satisfactorily obtained around 1.88 and 2.39 GHz by simultaneously employing the triple resonance, thus revealing a small FR of 1.27. Moreover, the dual operation bands hold stable in-band gains of about 2.8 and 3.5 dBic. In addition, the CP antenna still maintains the single-layer, single-fed, and single-radiator properties, which evidently confirms the validity and effectiveness of the proposed design.