A Dielectric Resonator Fed Wideband Metasurface Antenna With Radiation Pattern Restoration Under its High Order Modes

In this article, a dielectric resonator (DR) excited wideband metasurface (MTS) antenna with differential feeding is proposed, which uses two modes of the MTS and the fundamental mode of the DR to achieve multimode operation and obtain wide bandwidth. Initially, based on the characteristic mode theory, relevant modes of the MTS are analyzed. Then, a DR operating at the fundamental mode ( ${\mathrm {TE}}_{\delta 11}^{\mathrm {x}}$ ) is introduced as the magnetic current source to feed the MTS, exciting the dominant mode and high order mode (HOM) of the MTS simultaneously. However, this HOM has a weak gain at the broadside direction and large side lobes. According to the superposition principle of radiation patterns, the maximum at the broadside generated by the DR is utilized to enhance the boresight gain of the HOM, thus transforming the top-weak radiation pattern of this HOM into a broadside one and improving the gain flatness. Additionally, the differential feeding technique is introduced to improve the asymmetry of radiation pattern. Furthermore, by analyzing the out-of-phase currents and the periodicity of the MTS patches, three measures —loading transverse open-ended slots, shortening periodicity and loading longitudinal slots— are introduced to reduce the high side lobe level of the HOM while preserving radiation patterns undistorted and improving the gain stability. As a result, this HOM and the dominant mode of the MTS are combined with the fundamental mode of the DR, achieving multimode operation. Finally, the proposed antenna was fabricated and measured. The measured results agree well with the simulated ones, indicating an impedance bandwidth of 51.4% (4.38-7.41 GHz), a 5–9 dBi in-band gain and a 15 dB front-to-back ratio (FBR) within the operating band.