# Wideband Millimeter-Wave Perforated Hemispherical Dielectric Resonator Antenna
###### Abstract  
This paper presents a novel wideband circularly polarized millimeter-wave (mmWave) hemispherical dielectric resonator antenna (HDRA). Two distinct configurations of alumina dielectric resonator antennas (DRAs) are investigated, each featuring a different coating: the first configuration incorporates a polyimide layer, while the second involves a perforated alumina. Both configurations demonstrate promising characteristics, including impedance and axial ratio (AR) bandwidths of 58% and 17.7%, respectively, alongside a maximum gain of 10 dBic at 28 GHz. Leveraging additive manufacturing technology, the HDRA with the perforated coating layer is fabricated, simplifying assembly and eliminating potential air gaps between layers, thereby enhancing the overall performance. This innovative approach yields a circularly polarized (CP) HDRA suitable for Beyond 5G (B5G) communication systems. Agreement between measurements and simulations validates the efficacy of the proposed design, affirming its potential in practical applications. additive manufacturing; circular polarization; dielectric resonator antenna; millimeter wave 202413390/10/39/10/15/1  
fundamental modes. The radiation pattern of the TE\({}_{111}\) mode resembles that of a short horizontal magnetic dipole, while the TM\({}_{101}\) mode exhibits characteristics akin to a short electric monopole. Consequently, the diverse array of modes renders the hemispherical DRA (HDRA) appealing for various applications. The subscripts \(n\), \(m\), and \(s\) denote variations in fields along the elevation (\(\theta\)), azimuth (\(\phi\)), and radial (\(r\)) axes of the spherical coordinate system. It is well known that a substantial increase in the impedance bandwidth can be achieved by appending a dielectric coat to the DRA [6] since it acts as a transition zone between the antenna and the free space. Recent reports indicate that the DRA coating can increase gain, circular polarization, and impedance bandwidths [7; 8]. As an example, a wideband slot-fed multi-layer hemispherical DRA has been reported with an impedance bandwidth of 55% by exciting the TE\({}_{111}\) and TE\({}_{221}\) resonance modes in combination with the slot's resonance mode [9]. There have also been suggestions that a coaxial probe fed three-layer hemispherical DRA can be adopted in conjunction with materials that have relative permittivities of 9, 4 and 3 for the inner, middle, and outer layers, respectively, wherein a bandwidth of 65.6% has been realized with a lower gain of 3.2 dBi when lower-order modes of TM\({}_{101}\) and TM\({}_{102}\) are excited [10]. However, as mentioned earlier, probe feeding is impractical at mmWave frequencies. An alternative design of a three-layer hemispherical DRA has been reported using a rectangular waveguide feed whereby the optimization of the outer layer's permittivity renders the possibility of a broadband coupling to deliver impedance bandwidth and gain of 9.6% and 6.4 dBi, respectively, through the excitation of the TE\({}_{113}\) mode [11]. Another research study reported a wide impedance bandwidth of \(\sim\)25% in cases where a conformal strip is employed to excite a three-layer hemispherical DRA operating in the TE\({}_{111}\) fundamental mode [12]. A hemispherical DRA on a ground plane, fabricated using 3D printing technology with a conductive material, is presented in [13]. The antenna is optimized for operation in the C-band. Performance analysis reveals a bandwidth of return losses reaching 12.2%, along with an average and peak gain of 4.69 dBi. However, it is noted that utilizing probe feeding may significantly impact the antenna's bandwidth and efficiency, particularly in mmWave design scenarios. In [14], another design employing probe feeding is introduced. It explores a multi-layered cylindrical dielectric resonator antenna crafted with 3D-printing technology and tested at X-band frequencies. This design offers an impedance bandwidth of 65.7% (3.56-7.04 GHz) with a gain of 2.3 dB.