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LTCC slot array antenna for 5G application

Hiroyuki Takahashi, Satoshi Hirano, Daisuke Yamashita NGK SPARK PLUG CO., LTD.

Konan Bldg.6F, 2-5-7 Konan Minato-ku, Tokyo, 108-8601 Japan

Ph: +81-3-6872-1007; Fax: +81-3-6872-1014 Email: h-takahashi@mg.ngkntk.co.jp

Abstract

We develop the antenna module substrate which is broadband and large gain using an LTCC technology in a 28GHz band in this study. We used LTCC materials (dielectric constant 5.8, Dielectric loss 0.002@28GHz) which we developed for materials originally. First of all, we confirmed ability of slot array antenna made by LTCC for 5G application to get broadband property. The structure of designed array antenna became 40mm x 3.2mm x t1.6mm. We confirmed that this antenna has wider bandwidth (2.2GHz) and higher gain (6dBi). But this antenna size is too large for applying mobile device. Therefore we redesigned to reduce antenna size without specification degradation. The structure of redesigned antenna element becomes basically 4.8mm x 6.7mm x t1.0mm. This antenna has wider bandwidth (2.7GHz). The gains are more than 5dBi for the characteristic of this element in a band. Assume this antenna a fabric; 2 x 2 (4 elements: for mobile device) and 4 x 4 (16 elements: for small cell base station) we make an array antenna for Small cell base station and for mobile device. We will evaluate a beam steering examination with emission properties (gain, beam angle). Key words 5G, Millimeter wave, Antenna, LTCC, Slot array

I. Introduction With explosive growth of mobile demand, the fifth

generation (5G) mobile network would exploit the enormous amount of spectrum in the millimeter wave (mm-wave) bands to greatly increase communication capacity. [1] 5G systems have a need for significant performance improvements compared with LTE systems. For example, (1) enhanced mobile broadband (eMBB), with data rates of 1 Gbps. or higher, (2) ultra-reliable low latency communication (URLLC), less than 1ms, (3) massive machine type communication (mMTC), to provide seamless service everywhere.[2] For eMBB application, mm-wave is suitable, because a large amount of underutilized band can be leveraged to provide the Gigahertz transmission bandwidth. [3]

For 5G systems, several antennas evaluate to achieve eMBB specification. [4]- [6] For the most antenna designer, patch antenna is studied.

On the other hand, in mm-wave application, slot array antenna is one of the general designs. Several evaluations carry out for mm-wave communication. Slot array antenna is relatively easy to achieve wide band. It is suitable for 5G

(eMBB) application needs Gigahertz transmission bandwidth. [7]- [11] LTCC (low temperature co-fired ceramic) has good electrical properties for mm-wave application. By using LTCC technology, SIW (substrate integrated waveguide) slot array antenna also studied for mm-wave application. [12][13] We apply these technologies for antenna development to obtain broadband property for 5G communication. II. Slot array antenna design

To confirm the efficiency of the slot array antenna for broadband and large gain, we firstly design it by using LTCC (NOC) material. This material developed originally. NOC material has good performance for high frequency (Dielectric loss 0.002@28GHz). Table 1 shows material properties of NOC. By using this material, we design substrate integrated waveguide (SIW) to construct slot array antenna. We design SIW which had 20GHz cut-off. The dimension of SIW is 3.2mm (transvers spacing) and 1.6mm (Vertical spacing). This SIW is constructed by metallic plane and metallic via array in LTCC multilayer. The conductor

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used for metallization and via is Cu. Metallic via array locate at less than λ/10 intervals. Slot is design on top side of SIW and slot size is changed each other to obtain broadband property. Fig.1 shows photograph of slot array antenna

Table 1 Material properties of NOC. Dielectric constant

Dielectric loss

Metallization material

5.8 (@28GHz) 0.002 (@28GHz) Cu

Fig.1 Developed slot array antenna

The simulated and measured |S11| of this antenna are

shown in Fig. 2.

(a) Simulated data

(b) Measurement data

Fig.2 Reflection property of designed antenna The measured and simulated results are in good agreement.

The bandwidth for |S11| <10 dB is 2.2GHz (26.8~29.0GHz). The measured gain of this antenna is shown Fig.3.

Fig. 3 Measured gain of designed antenna

Flat gain response is obtained over the operating bandwidth

of 2.2GHz. Broadband and high gain antenna is obtained by using slot array antenna made by LTCC technology. But this antenna size is too large for applying mobile device.

III. Miniaturization of antenna To reduce antenna size, redesign conduct without property degradation. Based on previous result, SIW size and structure are optimized. As a result, small size antenna is designed. The structure of redesigned antenna element becomes basically 4.8mm x 6.7mm x t1.0mm. Fig 4 shows design of modified antenna.

(a) CAD image (b) Photograph

Fig. 4 Modified antenna image This antenna has 2 slots inside of dielectric. The reflection and gain properties are shown in Fig. 5.

For the modified antenna properties, the bandwidth for |S11| <10 dB is 2.7GHz (26.5~29.2GHz), and flat gain response is obtained over the operating bandwidth of 2.7GHz. This modified antenna achieve 1/8 volume miniaturization without property degradation.

40mm 4mm

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(a) Reflection property

(b) Gain property

Fig. 5 Reflection and gain properties of modified antenna Based on this result, two type of array antennas evaluate.

One is 2 x 2 (4 elements) array antenna for mobile device application. The other is 4 x 4 (16 elements) array antenna for base station application. Fig. 6 shows design of 2 x 2 antenna array.

(a) CAD image (b) Photograph

Fig. 6 Array antenna for mobile device application For the 2 x 2 array antenna, the bandwidth property change.

The reflection behavior around 27.5 GHz is slightly bigger than single element. It probably cause impedance mismatch between antenna and divider circuit. On the other hand, gain property is not observed the effect of mismatch. Gain becomes higher by array factor and flat gain response is obtained over the operating bandwidth of 2.7GHz. (Fig. 7)

(a) Reflection property

Fig. 7 Reflection and gain properties of array antenna (2 x2) Fig.8 shows design of 4 x 4 antenna array. The bandwidth property still remained. The bandwidth for |S11| <10 dB is 2.7GHz (26.5~29.2GHz). Gain becomes higher by array factor. Gain becomes higher (Max. 13dBi) by array factor and flat gain response is obtained over the operating bandwidth of 2.7GHz. (Fig.9)

(a) CAD image (b) Photograph

Fig. 8 Array antenna for base station application

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(a) Reflection property

(b) Gain property

Fig.9 Reflection and gain properties of array antenna (4 x 4) In case of 4 x 4 array antenna, to evaluate beams scan behavior, 4 antennas gather one port and RF power (28GHz) controlled phase input each port (4port). Fig.10 shows the constitution of beams scan evaluation. Maximum beam scan angle (-3dBi toward 0degree peak gain) is +-45 degree. (Fig. 11)

Fig. 10 Constitution of beams scans evaluation

Fig. 11 Result of beams scan evaluation @28GHz

IV. Conclusion We developed broadband and flat and high gain antenna by

using SIW made by LTCC. Antenna element size is relatively small for SIW slot array antenna, and almost equal to half of wavelength in air at 28 GHz. By using this small antenna element, we evaluate array antenna for base station and mobile device application. Higher gain by array factor could be obtained and broadband property also remained. But some mismatch still observed each array antenna. We confirmed beams scan can operate for base station application evaluation.

From now on, we will development antenna module includes RFIC, and other antenna design for further improvement for mm-wave communication.

Acknowledgment The authors would like to thank Tatsuya Adachi and Ikuro

Aoki, both from MODECH Inc., for their help, particularly in antenna design and evaluation. References [1] Young Niu,”A Survey of Millimeter Wave (mm Wave)

Communication for 5G: Opportunities and Challenge”, Wireless Networks, vol.21, Nov. 2015, pp. 2657-2676

[2] Marco Giordani, “Initial access in 5G mm-Wave Cellular Networks”, IEEE communications Magazine, vol.54 (11), pp.40-47

[3] Zhen Gao, “MmWave Massive MIMO Based Wireless Backhaul for 5G Ultra-Dense Network”, IEEE Wireless communications, vol. 22(5), pp. 13-21

[4] Huan-Chu Huang, “Influence Analysis of ZrO2 Ceramic for Cellular Phone an 5G mm-Wave Antenna Performance”, IEEE Asia-Pacific Conference on Antennas and Propagation, 2018, pp.420-424

[5] Mohsen Khalily, “Design of Phased Arrays of Series-Fed Patch Antennas With Reduced Number of the Controllers for 28-GHz mm-Wave Applications”, IEEE Antennas and wireless propagation letters, vol. 15, 2016, pp.1305-1308

[6] Huan-Chu Huang, “Overview of Antenna Designs and Considerations in 5G Cellular Phones”, International Workshop on Antenna Technology, 2018

[7] Takafumi Kai, “A Coaxial Line to Post-Wall Waveguide Transition for a Cost-Effective Transformer between a RF-Device and a Planar

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Slot-Array Antenna in 60-GHz Band”, IEICE Transactions communications, May 2016, pp.1646-1653

[8] Sehyum Park, “Center Feed Single Layer Slotted Waveguide Array”, IEEE Transactions on Antenna and Propagation, June 2006, pp.1474-1480

[9] Kunio Sakakibara, “Design of Millimeter-wave Slotted-Waveguide Planar Antenna for Sub-array of Beam-scanning Antenna”, International Symposium on Antenna and Propagation, 2008

[10] M. Bozzi, “Review of substrate-integrated waveguide circuits and antenna”, IET Microwaves, Antenna & Propagation, 2010, pp.909-920

[11] Yijin Wang, “Novel Design of a Dual-band 5G mm-Wave Antenna Array integrated with a Metal Frame of a Cellular Phone”, Asia-Pacific Microwave Conference, 2018, pp.1582-1584

[12] Manju Henry, “Millimeter Wave Substrate Integrated Waveguide Antennas: Design and Fabrication Analysis”, IEEE Transactions on Advanced Packaging, vol. 32, Feb. 2009, pp.93-100

[13] Junfeng Xu, ”Bandwidth Enhancement for a 60GHz Substrate Integrated Waveguide Fed Cavity Array Antenna on LTCC”, IEEE transactions on Antenna and Propagation, vol. 59 Mar. 2011, pp.826-832