喇叭天线

Characterization of Millimeter Wave Phased Array Antennas in Mobile Terminal for 5G Mobile System

Jakob Helander, Daniel Sjöberg, Mats Gustafsson

Department of Electrical Information Technology

LTH, Lund University

Lund, Sweden Kun Zhao, Zhinong Ying

Network Technology Laboratory SONY Mobile Communications AB

Lund, Sweden

Abstract — This paper presents a characterization method for millimeter wave (mmWave) phased array antennas in the mobile terminal for 5G communication. Arrays of different antenna designs, operating at 28 GHz, are evaluated according to novel characterization methods in this context - the total scan pattern of the phased array and its respective coverage efficiency. The results show the relevance of evaluating antenna array designs according to these characteristics, and illustrate, by introducing pattern diversity through sub-array schemes, that the coverage efficiency can be enhanced.

I. I NTRODUCTION

For supporting high quality multimedia applications in future smartphones, the massive increase in mobile data rates creates new challenges regarding the development of the 5th generation mobile system. Due to shortage of frequency spectrum below 6 GHz, bands at the mmWave frequencies (10 – 300 GHz) have been widely suggested as candidates, as the considerably larger bandwidths could be exploited to increase the capacity and enable the user to experience several gigabits per second data rates [1-3]. However, moving from the much lower cellular carrier frequencies used today (700 MHz – 2.6 GHz) up towards the mmWave bands results in a much higher free space path loss, as can be seen from Friis’ formula:

R T T R 20log

. (1) Here, is the distance between the antennas, the carrier frequency, the speed of light, and R,T and R,T the power and gain for receiving and transmitting antenna, respectively. In order to compensate for this increase in path loss without applying additional power, the antenna gains in both base

station and mobile terminal need to be much higher than current cellular antennas. In the mobile terminal, the high gain could be realized by employing an antenna array, which is

made possible as the physical antenna element aperture

decreases with the increase of frequency. However, as gain is

increased the resulting beamwidth will be narrowed accordingly, which will reduce the coverage of the mobile terminal array. Phased array configurations introduce the beamsteering function, and enable the system to achieve a good

link when incoming signals are coming from different angles [2, 3], but the steering range will still be limited. Beamsteering using phased arrays as a concept is not new, but the idea of

utilizing it in mmWave spectrum using small form factor

antennas in the mobile terminal is just starting to be considered [4-6]. Thus, it is of great value to characterize mmWave phased

arrays in mobile terminals, not only according to classical standards, but also to consider their total scan pattern and achievable coverage with respect to a gain threshold level , see Fig. 1.

This paper introduces the total scan pattern and coverage efficiency, and presents simulated results of different phased arrays implemented in the mobile terminal and operating at 28 GHz, Moreover, some sub-array schemes have also been investigated in order to achieve pattern diversity and illustrate how the coverage efficiency can be enhanced.

II. C HARACTERIZING A RRAY P ERFORMANCE

Since mobile terminals are hand-held in non-fixed

positions, incoming signals are assumed to be isotropically distributed. Our simplified physical model assumes urban cell sizes of ~200 m with a link being established either through line-of-sight (LOS) or minimum number of reflections. A. Total Scan Pattern and Coverage Efficiency ( ) The total scan pattern is obtained from all array patterns corresponding to the different phase shifts, by extracting the

best achievable gain at every angular distribution point ( , ),

such as to the right in Fig. 1. The coverage area of a mobile terminal phased array antenna can be found from the total scan pattern coverage with respect to . The coverage efficiency

can thus be defined such as: C A

. (2) The total area is the whole surrounding sphere. will

depend on the parameters in (1), with the flexibility of adding

Fig. 1. Left: The total scan pattern of phased array gain, and how its coverage is evaluated with respect to a gain threshold level.

Right: Example of total scan pattern of phased array.

7978-1-4799-7815-1/15/$31.00 ©2015 IEEE AP-S 2015