A Single-Layer Circularly Polarized Antenna With Improved Gain Based on Quarter-Mode Substrate Integrated Waveguide Cavities Array

In this letter, a single-layer right-hand circularly polarized (RHCP) antenna with low-profile and improved gain based on quarter-mode substrate integrated waveguide (QMSIW) cavities array is proposed and experimentally validated. The proposed antenna consists of a central microstrip patch and four QMSIW cavities with the same dimensions, which are directly cascaded to the central patch. The E-field distribution of the proposed structure is similar to that of a circular SIW cavity working in the high-order TM
₁₂₀
mode. Due to the in-phase equivalent magnetic currents array formed by the fringing electric field of the radiation edges, a high RHCP gain with very low cross polarization in the broadside is achieved. Because of the high-order working mechanism, the antenna can be fed by a coaxial probe directly without any complex power distribution network. Measured RHCP gain of the antenna is up to 10.4 dBi at the center frequency point 5.78 GHz, which is in good agreement with the simulated results.