Antipodal Linearly Tapered Slot Antenna Array for Millimeter-wave Base Station in Massive MIMO Systems Runbo Ma * , Yue Gao ◊* , Laurie Cuthbert ◊* and Qingsheng Zeng ∆ * MPI-QML Information System Research Centre, Macao Polytechnic Institute, SAR Macao ◊ Queen Mary University of London, School of Electronic Engineering and Computer Science, London, United Kingdom ∆ Communications Research Centre Canada, Ottawa, Canada yue.gao@qmul.ac.uk Abstract—For massive MIMO systems, it is very challenging to have the large-scale antennas for a compact base station. This paper presents a 36 sub-sectors for a compact millimeter-wave base station. The antenna array for each sub-sector is comprised of 16 planar high-gain dielectric-loaded antipodal linearly tapered slot antenna (ALTSA) elements arranged in a 4×4 configuration. Down to 36 feed ports are required in a base station with 36×16 antennas. The realized gain of the antenna array is 25.6 dBi, and the half-power beam widths (HPBW) are 10.7° and 5.3° in H-plane and E-plane, respectively. I. INTRODUCTION Recently, efforts have been made to utilize the millimeter waves in mobile communication with high capacity, due to the fact that for given aperture areas of transceiver antennas, shorter wavelengths can propagate longer compared to longer wavelengths as the transmission at higher frequencies becomes more directional [1].It is possible to pack hundreds or thousands of antennas into a small area due to the short wavelength. Based on the facts, investigations have suggested that massive antennas should be configured in the millimeter- wave mobile broadband (MMB) base stations to accomplish the massive MIMO framework. Providing significantly improved signal strength, spatial degree of freedom for spectral efficiency improvement and interference suppression, massive MIMO technology can provide tremendous communication capacity. It is obvious that the design and configuration of antenna array is the key in the massive MIMO system. Literature [2] proposed a 12×4 horn antenna array with an aperture area of about 6.4λ×10.8λ for each MMB base station sector, which provides a net antenna plus beamforming gain of 26.28 dBi at the base station at boresight. However, the horn antenna often requires a large space to be embedded. Although many promising benefits can be achieved using massive MIMO technology, there are still challenges, such as the hardware cost associated with the RF elements, the complexity of signal processing resulted from the large number of branch signals, the total energy consumption greatly increasing due to the use of large number of antennas [3]. Authors of paper [3] proposed a system design by integrating an EM lens with the large antenna array, which has the capability of focusing the power of any incident plane wave passing through the EM lens to a small focal area of the antenna array, depending on the angle of arrival of the wave. This method can substantially reduce the number of required RF chains at the receiver. In [4], a practical 2D active antenna array configuration for Full Dimension MIMO systems is presented. Fed with a single port, a patch antenna array with 1×4 elements is referred to as sub-array, which has a gain of about 11.7dBi. The MIMO array comprised of 8×4 such sub- arrays can provide an array gain of 15dB theoretically, and needs a total of 32 ports and occupies an area of 4λ×8λ. This paper presents a demonstrative base station structure in Fig. 1, which has the benefits of massive MIMO system with a moderate number of RF chains. Each sub-sector has an HPBW of 10 in azimuth and can be steered in elevation. The focus of this paper is to design a high gain antenna array using millimeter-wave frequency at 38GHz with gain of at least 25dBi and half-power beam widths (HPBW) of 10 in azimuth. θ s =10° beam steered in elevation and fixed in azimuth sub-sector each normal sector is divided into 6 sub-sectors θ sa =θ s R Fig. 1. Sub-sector desgin for massive MIMO base station. II. DESIGN OF ANTENNA ARRAY In order to meet the design requirement and simplify the fabrication technology, we choose the tapered slot antenna as the element of the antenna array due to its high gain and simple structure. According to the structure of antenna proposed in paper [5] , an antipodal linearly tapered slot antenna (ALTSA) operating on 38GHz band is modeled and simulated in the electromagnetic simulation software of CST Microwave Studio. Fig. 2(a) shows the structure of the dielectric-loaded ALTSA 1121 978-1-4799-3540-6/14/$31.00 ©2014 IEEE AP-S 2014