# Quasi-Yagi Slotted Array Antenna with Fan-Beam Characteristics for 28 GHz 5G Mobile Terminals
## 1 Introduction  
Millimeter-wave (mm-wave) array antennas have been widely studied for 28 GHz 5G mobile terminals [1; 2; 3]. The mm-wave band has been considered for 5G communication due to its increased channel bandwidth for higher data rate services [4]. In mm-wave communications, a high gain with beam-forming capability is required to compensate for the high free-space path loss due to atmospheric absorption [5]. Since the high gain can be obtained by using a directional beam, the mm-wave array antenna should have beam steering characteristics with a proper radiation pattern to have wide communication coverage. Therefore, a phased array antenna with beam steering characteristics is necessary to realize mm-wave communications [6]. Beam steering with a fan-beam pattern is an effective way to achieve wide beam coverage. The number of antennas to achieve wide beam coverage can be minimized by using a phased array antenna with a fan-beam pattern. Wide half-power beamwidth (HPBW) is needed to minimize the shaded area along the \(\pm x\) direction and hemispheric beam coverage that is required in mobile communications can be achieved by fan-beam steering along the \(\pm y\) direction, as shown in Figure 1a,b [2; 3]. Fan-beam antennas were reported for mm-wave 5G applications in [2; 3; 7; 8; 9; 10; 11]. In [3], a \(1\times 8\) phased array antenna with enhanced HPBW using air-hole slots was proposed for 28 GHz 5G mobile applications. The array antenna has a fan-beam pattern with a HPBW of 219\({}^{\circ}\) with a peak gain of 11.15 dBi, and it has \(\pm\)45\({}^{\circ}\) beam steering characteristics. Despite its great performance, the phased array antenna proposed in [3] is composed of electric dipole antennas. Radiation performance of the electric-type antenna is sensitive to the human body and thischaracteristic is not appropriate in mobile terminal applications [12]. In [7], the proposed antenna was constructed in a substrate-integrated waveguide (SIW) cavity structure to radiate the fan-beam of 133\({}^{\circ}\) HPBW. However, the cost of fabricating the SIW structures is prohibitive. In [8], a 1 \(\times\) 4 SIW open ended array antenna was proposed. The proposed antenna has a fan-beam pattern with a HPBW of 180\({}^{\circ}\). However, the antenna is composed of multilayer PCB boards with the SIW technique, and this manufacturing complexity leads to an increase in cost. In [9], a 16 \(\times\) 1 mesh grid array was proposed for 28 GHz 5G cellular applications. The array antenna has a fan-beam characteristic of 109\({}^{\circ}\) HPBW with a maximum gain of 10.9 dBi. However, this beamwidth performance is not wide enough for the beam coverage required by 5G applications. In [10], a 1 \(\times\) 8 slotted array antenna with an artificial magnetic conductor (AMC) reflector was proposed for hemispherical beam-coverage in 5G mm-wave applications. The AMC-backed slotted array antenna has a fan-beam pattern with a HPBW of 142\({}^{\circ}\) with a peak gain of 11.8 dBi. However, the separation distance of 1.9 mm (\(\approx\)0.31 \(\lambda\) at 28 GHz) is required between the radiator and the AMC surface, and the overall size is not suitable for mounting on mobile terminals. In [11], a 4 \(\times\) 1 Vivaldi antenna array was proposed for 5G mobile terminals. The proposed end-fire antenna array has a fan-beam characteristic with a HPBW of 165\({}^{\circ}\) in the elevation plane. However, design complexity is increased due to the multi-layer structure composed of a 10-layer PCB and shorting vias. In this paper, a quasi-Yagi slotted array antenna with fan-beam characteristics is proposed for 28 GHz 5G mobile terminal applications. The antenna consists of a 1 \(\times\) 8 slot antenna array and directors to achieve wide fan-beam characteristic. Slits are employed between adjacent slot radiators to yield high isolation characteristics by suppressing the flow of the surface current on the ground plane and surface waves on the substrate.