1. Introduction

As more high speed is required, many 5G communication systems have been proposed. While there are a lot of technologies for the 5G communication system, multiple-input multiple-output (MIMO) system is a basis for the 5G communication system. MIMO system has been proposed to increase spectral efficiency and diversity gain in wireless communication. The MIMO technology enhances the spectral efficiency and diversity gain by utilizing multiple antennas, because the multiple antennas provide multiple channels [1, 2]. In order to obtain multiple channels, the antenna elements have to be separated from the other antenna elements with larger gap than half-wavelength distance. However, it is difficult to increase the number of antennas because the antenna size is limited in wireless communication.

To enhance the spectral efficiency with compact antenna size, dual-polarization antenna array has been used for 5G technology [3]. It is possible to obtain two uncorrelated channels using the orthogonality of the dual-polarization antenna. However, the dual-polarization antenna still has limitation to increase the spectral efficiency without expanding antenna space.

It has been studied to enhance the spectral efficiency without increasing antenna space by using multiple radiation patterns of the antennas [4–7]. It was theoretically proposed that six times of spectral efficiency can be obtained compared to a single antenna by using three electric dipoles and three magnetic dipoles allocated at the same position. It means that the multiple antennas can be integrated within a compact size and provide multiplexing gain. Thus, the MIMO system can increase the spectral efficiency by not only using larger antenna array size but also combining multiple radiation patterns.

2.1 MIMO channel model

Array Pattern Based on Integrated Antenna DOI: http://dx.doi.org/10.5772/intechopen.81087

be expressed as

H can be described as

vector with the columns of A.

described as [1]

case.

j τ�ιþ2

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We consider a MIMO channel with a transmit and receive system, which is equipped with Nt antennas and Nr antennas, respectively. The received signal y can

where H is the Nr � Nt MIMO channel, x is an Nt � 1 transmit signal and n is an Nr � 1 complex Gaussian noise. Based on spatial fading correlation, the elements of

where H<sup>w</sup> is an Nr � Nt Rayleigh fading channel with uncorrelated and zero mean

NrNt � NrNt covariance matrix and ð Þ� † and <sup>E</sup>f g� are Hermitian and expectation operator, respectively [1]. Here, vecð Þ A is a vectorization operation to produce a

We assume that the sizes of the transmit and receive antenna are negligible compared to the distance between the transmit system and the receive system.

0

<sup>H</sup><sup>r</sup> <sup>H</sup>wR<sup>1</sup>=<sup>2</sup>

This channel model is called by the Kronecker model of MIMO system in general

There are spherical vector wave (SVW) modes which are orthonormal basis functions for arbitrary radiation pattern [10–12]. The radiation pattern of an arbi-

where ^<sup>r</sup> is the direction of the radiation, <sup>A</sup>ινs<sup>τ</sup>ð Þ¼ ^<sup>r</sup> <sup>A</sup>αð Þ¼ ^<sup>r</sup> <sup>A</sup>θ,αð Þ^<sup>r</sup> <sup>A</sup>ϕ,αð Þ^<sup>r</sup> � � is <sup>α</sup>th SVW mode with the multi-index <sup>α</sup> <sup>¼</sup> <sup>2</sup> ι ιð Þ� <sup>þ</sup> <sup>1</sup> <sup>1</sup> þ �ð Þ<sup>1</sup> <sup>s</sup> <sup>ð</sup> <sup>ν</sup>Þ þ <sup>τ</sup>, <sup>α</sup>max is the maximum number of SVW modes, Að Þ^r is an αmax � 2 matrix containing the row vector

Aαð Þ^r and t is an αmax � 1 vector with the element T<sup>α</sup> which is the transmitting coefficient of the transmitter antenna [10]. The SVW mode Aαð Þ^r is described well in Appendix. In order to decompose the radiation pattern of a receiver antenna, the

TινsτAινsτð Þ^r

<sup>T</sup>αAαð Þ¼ ^<sup>r</sup> <sup>k</sup> ffiffiffiffiffi

2η p A<sup>0</sup>

ð Þ^r t,

(5)

R<sup>h</sup> ¼ R<sup>0</sup> Ht

<sup>H</sup> <sup>¼</sup> <sup>R</sup><sup>1</sup>=<sup>2</sup>

Kronecker product operator, respectively. Therefore, the MIMO channel can be

<sup>h</sup> <sup>¼</sup> vecð Þ¼ <sup>H</sup> <sup>R</sup><sup>1</sup>=<sup>2</sup>

entries which follow complex Gaussian distribution, Rh <sup>¼</sup> <sup>E</sup> hh† � � is the

Then, the covariance matrix of the MIMO channel is given by

where <sup>R</sup>H<sup>r</sup> <sup>¼</sup> <sup>E</sup> HH† � �, <sup>R</sup>H<sup>t</sup> <sup>¼</sup> <sup>E</sup> <sup>H</sup>†<sup>H</sup> � � and ð Þ�

2.2 Spherical vector wave-based channel model

trary transmitter antenna is described as

<sup>F</sup>ð Þ¼ ^<sup>r</sup> <sup>k</sup> ffiffiffiffiffi

2η p ∑ ιmax ι¼1 ∑ ι ν¼0 ∑ 2 s¼1 ∑ 2 τ¼1 j τ�ιþ2

<sup>¼</sup> <sup>k</sup> ffiffiffiffiffi 2η p ∑ αmax α¼1 j τ�ιþ2

y ¼ Hx þ n, (1)

<sup>h</sup> vecð Þ H<sup>w</sup> , (2)

⊗RHr, (3)

and ⊗ are matrix transpose and

<sup>H</sup><sup>t</sup> : (4)

On the other hand, there have been studies of array optimization technologies for the linear antenna array according to various objective functions [8, 9]. This antenna array could have better interference cancelation using genetic algorithms. Then, it is also possible to enhance the spectral efficiency and diversity gain by combining the array optimization technologies and the integrated antenna-based array system.

In this chapter, we introduce an integrated antenna array which is a type of the MIMO systems. The integrated antenna array consists of multiple array elements, and the array element has multiple antenna elements. Each antenna element of the integrated antenna has different radiation patterns to increase the spectral efficiency in wireless communication area. The purpose of this chapter is to introduce the concept of the integrated antenna array and to show the possibility to apply it practically to wireless communication technology. We will also explain a framework for next-generation technology so that we can provide further works as well.

We organize the chapter as follows. In Section 2, we explain channel models for the integrated antenna array. In Section 3, several practical integrated antennas are introduced to verify that the integrated antenna array can be implemented practically. In Section 4, we verify the performance of the integrated antenna array in urban macro-cell environment compared with mono-polarization and dualpolarization dipole antenna arrays.
