# Wideband Millimeter-Wave Perforated Hemispherical Dielectric Resonator Antenna
###### Abstract
However, it is difficult to precisely fix a conformal strip on the DRA surface at mmWave frequencies due to the smaller dimensions and potential air gaps between the strip and DRA. Another slot-coupled three-layer hemispherical DRA design offers a broad impedance bandwidth in the region of 29% with a gain of 4.4 dBi proposed by exciting the fundamental TE\({}_{111}\) resonance mode [15]. When the performance of a two-layer hemispherical DRA is compared to that of a single-layer counterpart, it becomes evident that there is a broader bandwidth of 31.9% and a gain of 2.5 dBi for the layered DRA compared to 14% for the single-layer DRA that operates at the TM\({}_{101}\) lower order mode [16]. On the other hand, multi-layer DRA configurations are associated with known limitations, such as the increased physical size and the complex assembly procedure with respect to bonding the different dielectric layers together with no potential air gaps in between. This study addresses the above issue by utilizing 3D printing technology to fabricate a DRA and perforated coat configuration using alumina. It should be noted that innovative 3D printing technology is simple, cost-effective, and has a short fabrication cycle. Hence, it has recently been considered in the context of DRA fabrications as it eliminates the potential air gaps more effectively than other fabrication techniques [17; 18]. In this paper, we introduce a novel approach wherein the traditional layered hemispherical dielectric resonator antenna (DRA) geometry is replaced with an alumina structure comprising two distinct sections: an inner solid DRA and an outer perforated coat featuring a considerably lower effective dielectric constant. This structural modification enables an automated 3D printing process, obviating the requirement for labor-intensive assembly and bonding of numerous solid dielectric layers. Moreover, utilizing the same material for both the DRA and the coat optimizes the 3D printing procedure, thereby enhancing overall efficiency. It is noteworthy that prior research, as documented in [19], has introduced a 3D-printed cylindrical DRA with a perforated coat, achieving optimal performance through the utilization of a cross-slot topped by a thin alumina layer to enhance coupling. Conversely, in our proposed hemispherical DRA (HDRA), optimal performance is attained through the implementation of a spiral slot. This discrepancy in performance stems from variations in the electromagnetic field distribution within the two DRAs. Additionally, the perforated coat layers exhibit differing numbers and sizes of air gaps in the respective DRAs. Consequently, maximum coupling to the HDRA is achieved without necessitating the addition of a thin alumina layer between the HDRA and the spiral slot. Previous research on multi-layer hemispherical DRAs has primarily focused on enhancing impedance bandwidth, overlooking opportunities to widen the CP bandwidth, despite the potential afforded by the outer section to introduce an additional degree of freedom. Another contributing factor to the expanded CP bandwidth is the incorporation of an Archimedean spiral slot to feed the antenna, which excites multiple higher-order modes. Operating within the 18.4-33.4 GHz mmWave frequency band, the antenna demonstrates impressive impedance and axial ratio bandwidths of approximately 58% and 17%, respectively, surpassing those reported in earlier studies for circularly polarized hemispherical DRAs. The paper is organized as follows: Section 2 introduces the proposed two configurations of the HDRA; Section 3 presents the measured results obtained from prototypes of the two HDRA configurations; and Section 4 offers concluding remarks and summaries. Simulations were conducted using CST Microwave Studio version 2020, and the results closely aligned with experimental measurements.