**Abstract**

Indoor positioning systems based on radio wave have drawn a lot of research interest over the last few decades. One of the positioning methods, Angle of Arrival, locating object based on the relative angle of object to the reference points, requires a directional antenna in order to improve the accuracy of indoor positioning system. From this situation, an eight-port phased array antenna using reflection type phase shifter is designed. The input power is split to each antenna through eight-port Wilkinson power divider with insertion loss of about 11 dB and isolation of about 20 dB. To extract more accurate position, the main beam of phased array antenna can be steered smoothly by a design 18 of a continuous and full 360° reflection type phase shifter with low insertion loss variation. Microstrip patch antennas are used as elements in phased array antenna. The steering of main beam is presented by radiation patterns of phased array antenna, measured in anechoic chamber from 45 to 45° with step 5°. The measurement result shows that the main beam direction is quite close to the desired direction in simulation. In most case, the side lobe level is less than the main lobe about 10 dB.

**Keywords:** angle of arrival (AoA), antenna array, beamforming, phased array, low loss, phase shifter, steering beam

### **1. Introduction**

Nowadays, positioning has played an important part in daily life and is the foundation for many other applications such as navigation, tracking, location-based services, and games. While outdoor positioning has become widespread and popular with satellite-based navigation systems, that is, GPS, GLONASS, and Galileo, indoor positioning systems have attracted a lot of research interest over the last decade. Indoor localization promises to create a lot of new services such as guiding users in museum, preventing thefts from valuable assets, locating products in supermarkets, navigating in mall, saving power consumption of electronic devices, and so on.

Due to scattering and attenuation of microwave on roofs, walls, and other objects, the systems for outdoor positioning are infeasible solutions when applying to indoor positioning. Instead, indoor positioning systems have been implemented based on several technologies: infrared (IR) [1], bluetooth [2, 3], radio-frequency

identification (RFID) [4], wireless local area networks (WLAN) [5], ultrawideband [6], ultra-sound [7], magnetic positioning [8], and audible sounds [9]. Among them, WLAN-based approach appears to be among the most suitable solutions owing to its wide range and the popularity of equipment. Nowadays, WLAN devices can be found in almost all civil and commercial properties due to their ease of installation and usage. The number of WLAN devices has reached billions and is continuously increasing day by day, as a result, the study in WLAN-based indoor positioning promise to be applied and spread in the near future. Besides, with the current 5G supports, this indoor positioning technology can even attain to longer reach, greater capacity, high accuracy, and reliability.

antenna elements, power dividers, feed network, and phase shifters. In Section 4, we verify the performance the printed antenna array by the Vector Network Ana-

Phased array antenna is a multiple antenna system in which antenna elements are fed coherently with variable phase or amplitude control to provide for pattern shaping [14]. The concept of phased antenna array was introduced in military applications in the 1940s and first used for military applications for several decades. It improved the reception and transmission patterns of antennas and enabled the antenna system to be electronically steered to receive or transmit information from a particular direction without mechanically moving the structure, which cannot be obtained by any single antenna type. Furthermore, in applications for long distance communication, an antenna design with very high directive characteristics is required. As a single antenna usually provide low directivity and gain with wide radiation pattern [15], an array of antennas with high directivity gain is usually used to meet that demand. Recent growth in civilian radar-based sensors and communication systems has drawn increasing interest in utilizing phased array technology for commercial applications. In most cases, the antenna elements in an array are identical to conveniently adjust the directivity and other parameters of the array. Besides, the antenna elements can be arranged in different geometries to create different beams. The complexity of system increases according to the array geometry. The total beam of the array is a combination of the fields radiated by each antenna elements. The fields of elements will interfere constructively to reinforce in desired directions and interfere destructively to cancel in undesired directions in order to provide directive patterns. The influence of element fields on total beam is considered as array factor and the beam steering principle is based on the change of array factor. In addition, feeding techniques also contribute to the array performance and feed network is the most important component since it supplies the signals to the whole antenna structure and determines the amplitude and phase of

**2. Design factors of beamforming phased array antenna**

*Beamforming Phased Array Antenna toward Indoor Positioning Applications*

electromagnetic waves in order to create the desired beam.

As mentioned in [15], the geometrical configuration of the overall array may be linear, planar, circular, spherical, etc. For each case, the effective field distribution and mutual coupling will be different from one another. A linear phased array is where the antenna elements are aligned along a straight line, called the array axis. Normally, identical antennas with equal distances are selected in order to simplify calculation as well as beam control. An array of identical elements all of identical magnitude and each with a progressive phased is referred to as a uniform array [15].

The distance between two antenna elements is called element spacing d in **Figure 1a**. For linear phased array, the main beam can only scan along the x-axis, and the angle θ represents the "angle of arrival" of the radio waves. A planar phased array antenna is a set of antennas located in a plane with equal spacing between N elements (dy) in each column and M elements (dx) in each row, as shown in **Figure 1b**. By adjusting the magnitude and phase of incoming wave for each antenna, the main beam of this structure can be steered along two x- and y-axis. Therefore, it can provide a 2D angular scan, both horizontal ϕ and vertical θ scans. With this advantage, planar phased array antennas are being used in smart antenna

**2.1 Array geometry**

**97**

lyzer and in anechoic chamber.

*DOI: http://dx.doi.org/10.5772/intechopen.93133*

For WLAN-based approach, indoor localization techniques are classified into RSS scene analysis, ToA, TDoA, RToF, and AoA [1]. While the highly unstable feature of RSS in indoor environments is the major challenge of RSS scene analysis technique and ToA, TDoA, and RToF are based on a precise clock synchronization of devices, the AoA technique requires a directional antenna design to estimate the relative angle of object to reference points.

There have been several antenna designs for AoA-based indoor localization presented in past few years. Giorgetti and Cidronali [10] introduced a switchedbeam directional antenna, including six circular antennas to cover six areas in a room. Rzymowski et al. [11] also introduced an antenna design using 12 passive elements electrically steerable parasitic array radiator antenna with one active monopole in the center of the ground plane. By controlling single-pole, single-throw switches, parasitic elements connect to the ground and act as reflectors, which change the main lobe's directions. With 12 passive elements, this antenna has 12 different directions. Kamarudin et al. [12] proposed reconfigurable antennas using PIN diodes to switch lumped components such as inductors and capacitors in order to change the structure of antennas and switch between four beams. Bui et al. [13] built a switch-beam array antenna based on 4 4 Butler matrix to create four beams toward four angles. It is found that these designs are based on switching between the limited number of predefined beams, which limits the resolution in determining the location of object and leads to significant errors in positioning.

For indoor localization, the system needs to determine the location of object with high accuracy. Therefore, an antenna design with high-resolution steering beam ability is very essential in the AoA technique. As discussed above, the current antenna designs for indoor localization system mainly focus on switched-beam antenna structures. With these structures, the resolution of angle of arrival primarily depends on the number of antenna elements. Therefore, to create a system with high resolution of beam scanning, the number of antennas as well as switching elements such as PIN diode, FET also increases, which makes the system more cumbersome and complex. In order to improve the accuracy for AoA-based indoor localization, the aim of this chapter is to study and develop a phased array antenna at Wi-Fi band (2.4 to 2.484 GHz), capable of finely steering beam without increasing the number of antennas.

This chapter addresses the subject of a beamforming phased array antenna, which plays the vital role for AoA-based indoor positioning system. The array antenna is designed to steer the main beam in high resolution without the increase of antenna elements as well as switching elements. The design of this antenna array has focused on developing the controllable 360° continuous reflection type phase shifter. This chapter is organized as follows. In Section 2, we explain the principles of forming beam and several methods to feed antennas and to control the phase differences for phased array antennas. In Section 3, we discuss the structure of phased array antennas used for practical indoor localization, advancing from

antenna elements, power dividers, feed network, and phase shifters. In Section 4, we verify the performance the printed antenna array by the Vector Network Analyzer and in anechoic chamber.
