Phased Array Antenna with Parasitic Slot Array for HPBW Enhancement in 5G Applications

Minbeom Ko1, Sungpeel Kim1, Youngwook Kim2, and *Jaehoon Choi1

1Department of Electronics and Computer Engineering, Hanyang University, 222, Wangsimni-ro, Seongdong-gu, Seoul 04763, Korea

2Electrical and Computer Engineering, Lyles College of Engineering California State University, Frenso, USA *choijh@hanyang.ac.kr (corresponding author)

Abstract- A 1ⅹ8 folded dipole phased array antenna with parasitic slot array is proposed to enhance the half power beamwidth (HPBW). Ground plane is modified to flare type for impedance matching at the center frequency of the target band (26.5 GHz – 29.5 GHz). In order to enhance the HPBW in H-plane, parasitic slots are embedded in the ground plane. The -10 dB reflection coefficient bandwidth of the proposed antenna is 4.47 GHz from 25.76 GHz to 30.23 GHz and the isolation between the two adjacent ports is higher than 20 dB over the target band. The HPBWs of the proposed antenna are 215° in H-plane and 12.4° in E-plane at 28 GHz, respectively. The simulated peak realized gain is 11.59 dBi at 28 GHz and the front-to-back ratio is 11.66 dB.

I. INTRODUCTION

With the rapid development of communication technologies, numerous devices can be connected together to support a variety of Internet-of-Things (IoT) applications, including smart grid, advanced metering infrastructure (AMI), smart devices, and etc [1]. Among the various potential frequency bands for 5G wireless communication, millimeter-wave (mm-wave) band is considered as a promising candidate for IoT applications because of its large capacity and high data rate [2]. Antenna is one of the key hardware elements required to support the fifth generation (5G) communications. However, there are several challenges to design a mm-wave 5G phased array antenna. The peak gain of the array antenna should be over 9 dBi to overcome the path loss and to satisfy the link budget. In addition, the beam scanning coverage and beamwidth should be wide to satisfy the required beam coverage [3].

Many researchers have studied various mm-wave 5G phased array antennas, such as folded dipole antenna array with the truncated ground plane [4], folded dipole antenna array with corrugated ground plane [5], and antipodal Vivaldi antenna array with decoupling structure [6]. Although, all aforementioned array antennas have peak gain of over 10 dBi, the half power beamwidth (HPBW) in H-plane is less than 169° which is not sufficient to achieve the hemi-spherical beam coverage for stable communication.

In this paper, we proposed a 28 GHz 1ⅹ8 folded dipole phased array antenna with parasitic slots in the flared ground plane for HPBW enhancement in H-plane. The simulated results show that the proposed antenna has good performance suitable for 5G mm-wave communication.

II. ANTENNA DESIGN AND SIMULATION RESULTS

A. Antenna Geometry (a) (b)

(c)

Figure 1. Geometry of the proposed antenna: (a) Front view of a 1ⅹ2 folded

dipole antenna array with a parasitic slot, (b) Side view, and (c) Front view of

the 1ⅹ8 proposed antenna array structure. (LGND = 12, WGND = 42.8, l1 = 2.4, l2

= 1.7, l3 = 3.3, l4 = 1.6, w1 = 0.2, w2 = 0.5, w3 = 2.3, g1 = 0.36, g2 = 5.35, hs =

0.127, α1 = 45°, α2 = 83°) (Unit: mm)

Figure 1 illustrates the geometry of the proposed antenna. The antenna is printed on the Taconic RF-35 substrate (εr = 3.5, tanδ = 0.0018) with a thickness of 0.127 mm. The bottom side of the substrate consists of half of dipole elements, parasitic slots, and the flared ground plane acting as a reflector. The microstrip feed line and another half of dipole elements are printed on the top side of the substrate. The overall size of the antenna is 42.8 mm ⅹ 12 mm.

B. Simulation Results

Figure 2. Simulated S-parameters comparison between the proposed array

antenna and the flat ground type.

Figure 3. Simulated radiation patterns at 28 GHz with and without parasitic

slot array.

(a) (b)

Figure 4. Simulated surface current distributions when the port 1 and port 2

are excited at 28 GHz: (a) Without parasitic slots and (b) With parasitic slots. Figure 2 shows the simulated S-parameters of the proposed

array antenna compared with those of a flat ground array antenna. As shown in Figure 2, the impedance matching characteristic is improved by modifying the ground plane to flare type. The simulated -10 dB reflection coefficient (S11)

bandwidth of the proposed antenna is 4.47 GHz (25.76 - 30.23 GHz) which is wider than flat ground case (26.61 - 30.61 GHz). The isolation between the two adjacent ports is higher than 20 dB with the separation distance of λ0/2 at 28 GHz. The good isolation level was achieved by folding the dipole elements. Figure 3 shows the simulated radiation patterns of the proposed array antenna at 28 GHz. The simulated peak gain of the

antenna array without parasitic slot array is 11.99 dBi and the FBR is 14.07 dB. The simulated HPBWs are 191° in H-plane and 12.5° in E-plane, respectively. The simulated peak gain of the proposed array antenna(with slot) is 11.59 dBi and the front-to-back ratio (FBR) is 11.66 dB. The simulated HPBWs are 215° in H-plane and 12.4° in E-plane, respectively. Even though the peak gain and FBR values are reduced slightly, the HPBW in H-plane is increased by 24°. To better understand the operation principle of the parasitic slot, the surface current distributions at 28 GHz with and without parasitic slots are illustrated in Figure 4. When port 1 and port 2 are excited simultaneously, the parasitic slot on the ground plane operates as a slot antenna due to the surface current flowing towards the nearest port through the ground plane, as shown in Figure 4(b). Therefore, the gain at the lower elevation angle can be improved by the additional radiation of parasitic slot array, whereas the gain at the boresight is barely affected.

III. CONCLUSION

In this paper, a 1ⅹ8 folded dipole phased array antenna with parasitic slot array is proposed. The simulated -10 dB S11

bandwidth fully covers the required frequency band. The simulated peak gain and FBR are 11.59 dBi and 11.66 dB, respectively. The simulated HPBW in H-plane is 215° and the HPBW enhancement is achieved by inserting slots in the ground plane. We are convincing that the proposed antenna is highly suitable for 5G applications.

ACKNOWLEDGMENT

This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIP) (No. 2017R1A2B4002811).

This work was supported by Institute for Information & communications Technology Promotion(IITP) grant funded by the Korea government(MSIT) (NO. 2019-0-01089, Development of low-frequency ultra-wide area antenna using conical beam pattern structure for remote water metering).

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