Phased Antenna Arrays toward 5G

*Tran Cao Quyen*

### **Abstract**

An antenna array for 5G has to be able to create multibeam (approximately dozens or hundreds of beams), wide azimuthal coverage (approximately 360°), and high gain (>20 dB). The analyses of four kinds of multibeam phased arrays, namely a multibeam ULA analog phased array (MULA-analog-PA), multibeam ULA digital phased array (MULA-digital-PA), multibeam cylindrical digital phased array (MCdigital-PA), and multibeam cylindrical analog phased array (MC-analog-PA), are performed. The analyses show that all arrays could provide multibeam with different complexities and computations but MULA-analog-PA and MULA-digital-PA are with maximum 180° of azimuthal coverage; whereas MC-analog-PA and MCdigital-PA are with unlimited azimuthal angle. The simulations of the MC-analog-PA with 32 10 elements (10 rings with each ring of 32 elements) show that the array could provide 32 beams symmetrical over 3600 azimuthal coverage with the directivity of 27 dB. The obtained results proved the effectiveness of the phased array antennas for 5G applications.

**Keywords:** phased array antennas, multibeam, azimuthal coverage, cylindrical geometry

### **1. Introduction**

5G will be at the heart of the future of communications in which the technologies such as new multiple accesses, massive MIMO, multiple beams, ultra-dense networking, etc. [1–4] are key technologies. 5G will bring new challenges for the designers of the physical infrastructure including antenna designers. Antennas for 5G have to be able to create multiple independent beams (approximately dozens or hundreds of beams), wide azimuthal coverage (approximately 360°), high gain (>20 dB), and acceptable complexity of feeding network for analog platform or powerful digital processing for digital one.

This chapter will present about multibeam phased array antennas toward 5G in terms of their principles of operation and theoretical limits. The analyses of four kinds of multibeam phased arrays, namely a multibeam ULA analog phased array (MULA-analog-PA), multibeam ULA digital phased array (MULA-digital-PA), multibeam cylindrical digital phased array (MC-digital-PA), and multibeam cylindrical analog phased array (MC-analog-PA), are performed, and some simulation results are given to demonstrate the performance of those arrays.

As is known, the phased array antennas were dating back from 60 to 80 decades with the main application of satellite communications and military radar [5–8]. In

accompany with the use of higher carrier frequencies of 5G [9–10], phased array antenna could be smaller and more compact in size with civilization application.

The principle of phased array is that the phase of each antenna element is controlled by using an analog phase shifter. Assuming the array has M elements, the

where *ψ* is the total phase difference of the fields of adjacent elements as

where *α* is the phase difference of adjacent elements, that is, element 2 with

*<sup>E</sup>* <sup>¼</sup> sin Mð Þ *<sup>ψ</sup>=*<sup>2</sup>

The array factor which is a ratio of total field E to its maximum is given by

The array factor of ULA with equal amplitude, equal spacing in Z-axis, and *α* ¼ 0 (Broadside Array) is illustrated in Cartesian coordinate in **Figure 2** as follows.

<sup>¼</sup> *<sup>E</sup>*

*<sup>ψ</sup>* <sup>¼</sup> <sup>2</sup>*π<sup>d</sup>*

After some manipulation, the total field E can be written as

*AF* <sup>¼</sup> *<sup>E</sup> E*max

*<sup>j</sup><sup>ψ</sup>* <sup>þ</sup> *<sup>e</sup> <sup>j</sup>*2*<sup>ψ</sup>* <sup>þ</sup> <sup>⋯</sup> <sup>þ</sup> *<sup>e</sup> j M*ð Þ �<sup>1</sup> *<sup>ψ</sup>* (1)

*<sup>λ</sup>* cos *<sup>ϕ</sup>* <sup>þ</sup> *<sup>α</sup>* (2)

sin ð Þ *<sup>ψ</sup>=*<sup>2</sup> (3)

*<sup>E</sup>*ð Þ *<sup>ψ</sup>* <sup>¼</sup> <sup>0</sup> (4)

total field E at a large distance in the direction Ѳ is given by

*E* ¼ 1 þ *e*

respect to 1, 3 with respect to 2, etc.

*Phased Antenna Arrays toward 5G*

*DOI: http://dx.doi.org/10.5772/intechopen.93058*

given by

**Figure 2.**

**67**

*The array factor of ULA-analog-PA.*

In order to create a main beam pointing into Ѳ direction, it is necessary to make phase progressive of a uniform linear array (ULA) with the phase difference of kdcosѲ between two consecutive elements [11]. In other words, a MULA-analog-PA having M antenna elements required M phase shifters. If this array needs N independent beams, the array must have a matrix of M N phase shifters [12].

Due to the complexity of the design of the MULA-analog-PA, the development of digital processing leads to the invention of digital beamforming of phased array. Performing the beamforming in a multibeam digital phased array antenna is a more flexible and versatile approach. For each antenna element, it has its own amplifying module but without any phase shifters or attenuators; but it required a strong central processing unit (CPU) in order to process beamforming algorithms [13, 14].

A MULA-digital-PA could create unlimited number of independent beams, but its azimuthal coverage could not be over 180°. It is intrinsic property of an ULA. To make a solution for this problem, we need to use the circular array [14] that has 360° beam coverage in azimuthal plane. Combining the advantage of multibeam and wide azimuthal angle leads to the construction of multibeam cylindrical phased array antenna in analog or digital beamforming. MC-digital-PA is preferred if a large numbers of beams and high computing performance are required, and MC-analog-PA is suggested if a moderate numbers of beams and low cost of computing performance are required.

#### **2. Multibeam ULA analog phased array (MULA-analog-PA)**

#### **2.1 ULA analog phased array (ULA-analog-PA)**

Let us introduce the subject of phase array antenna by considering the simplest situation, namely, uniform linear analog phased array (ULA-analog-PA). An array of identical elements (in this case, isotropic elements), all of identical magnitude and each with a progressive phase and arranging in a straight line, is referred to as a uniform linear array. A typical ULA-analog-PA in which each antenna element with equal spacing, *d*, is illustrated in **Figure 1**.

**Figure 1.** *A typical ULA-analog-PA.*

*Phased Antenna Arrays toward 5G DOI: http://dx.doi.org/10.5772/intechopen.93058*

accompany with the use of higher carrier frequencies of 5G [9–10], phased array antenna could be smaller and more compact in size with civilization application. In order to create a main beam pointing into Ѳ direction, it is necessary to make

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

phase progressive of a uniform linear array (ULA) with the phase difference of kdcosѲ between two consecutive elements [11]. In other words, a MULA-analog-PA having M antenna elements required M phase shifters. If this array needs N independent beams, the array must have a matrix of M N phase shifters [12]. Due to the complexity of the design of the MULA-analog-PA, the development of digital processing leads to the invention of digital beamforming of phased array. Performing the beamforming in a multibeam digital phased array antenna is a more flexible and versatile approach. For each antenna element, it has its own amplifying module but without any phase shifters or attenuators; but it required a strong central processing unit (CPU) in order to process beamforming algorithms [13, 14]. A MULA-digital-PA could create unlimited number of independent beams, but its azimuthal coverage could not be over 180°. It is intrinsic property of an ULA. To make a solution for this problem, we need to use the circular array [14] that has 360° beam coverage in azimuthal plane. Combining the advantage of multibeam and wide azimuthal angle leads to the construction of multibeam cylindrical phased array antenna in analog or digital beamforming. MC-digital-PA is preferred if a large numbers of beams and high computing performance are required, and MC-analog-PA is suggested if a moderate numbers of beams and low cost of

**2. Multibeam ULA analog phased array (MULA-analog-PA)**

Let us introduce the subject of phase array antenna by considering the simplest situation, namely, uniform linear analog phased array (ULA-analog-PA). An array of identical elements (in this case, isotropic elements), all of identical magnitude and each with a progressive phase and arranging in a straight line, is referred to as a uniform linear array. A typical ULA-analog-PA in which each antenna element with

computing performance are required.

**2.1 ULA analog phased array (ULA-analog-PA)**

equal spacing, *d*, is illustrated in **Figure 1**.

**Figure 1.**

**66**

*A typical ULA-analog-PA.*

The principle of phased array is that the phase of each antenna element is controlled by using an analog phase shifter. Assuming the array has M elements, the total field E at a large distance in the direction Ѳ is given by

$$E = \mathbf{1} + e^{j\mathbf{y}} + e^{j2\mathbf{y}} + \cdots + e^{j(M-1)\mathbf{y}} \tag{1}$$

where *ψ* is the total phase difference of the fields of adjacent elements as given by

$$
\psi = \frac{2\pi d}{\lambda} \cos \phi + a \tag{2}
$$

where *α* is the phase difference of adjacent elements, that is, element 2 with respect to 1, 3 with respect to 2, etc.

After some manipulation, the total field E can be written as

$$E = \frac{\sin\left(\mathbf{M}\varphi/2\right)}{\sin\left(\varphi/2\right)}\tag{3}$$

The array factor which is a ratio of total field E to its maximum is given by

$$AF = \frac{E}{E\_{\text{max}}} = \frac{E}{E(\nu = 0)}\tag{4}$$

The array factor of ULA with equal amplitude, equal spacing in Z-axis, and *α* ¼ 0 (Broadside Array) is illustrated in Cartesian coordinate in **Figure 2** as follows.

**Figure 2.** *The array factor of ULA-analog-PA.*
