**4.2 Beamforming antenna measurement evaluation**

#### *4.2.1 Material and facility preparation*

In general, the radiation pattern of an antenna is three-dimensional. Because it is impractical to measure a three-dimensional pattern, a number of two-dimensional patterns are measured. Patterns can be obtained by fixing one of angles (θ or ϕ) while varying the other. For a single antenna, the θ = π/2 azimuthal pattern and ϕ = 0 elevation pattern are usually chosen. For phased array antenna, only θ = π/2 azimuthal pattern is measured to observe the direction of main beam, and the ϕ = 0 elevation pattern does not provide useful information. Ideally, the measurement system would be placed in outdoor space in the far field region to cancel reflection waves. However, this ideal condition is not achievable; therefore indoor anechoic chambers have been developed for this antenna array measurement. The region inside anechoic chambers is covered with RF absorber. The reflection coefficient of anechoic chambers is about 40 dB [15, 37].

Structure of the measurement room is shown in **Figure 30**. A horn antenna, HF 906, is used as a transmitting antenna, and antenna under test (AUT) is received antenna. Thanks to the reciprocity property of antennas, the transmitting and receiving radiation patterns are identical. Therefore, the swap between two antennas is not necessary. The receiving and transmitting powers are measured by the PNA N5222A network analyzer in which the AUT is rotated through a rotating table. To automatically operate this system, a rotating table with an angle step of 5° is set up, and then the measured results are extracted and analyzed from the network analyzer.

**Figure 31** shows the radiation pattern of my microstrip patch antenna. We can see that the half power beam width is larger than 90° and the measured radiation pattern is similar to simulated one. Therefore, in terms of radiation pattern, each antenna element meets the requirement for indoor positioning system (**Figure 32**).

#### *4.2.2 Beamforming array measurement*

All components of the array including power divider, phase shifter, antenna, and controller are assembled together to form a phased array antenna. The radiation

patterns of phased array antenna are also measured in anechoic chamber at General Department of Technical Logistics of the Vietnamese Ministry of Public Security, similar to microstrip patch antenna at 2.45 GHz. The phased array antenna will be mounted in the rotating table to steer the main beam toward angles from 45 to 45° with step of 5°. The measured results are compared with simulated results in same coordinate to investigate the quality of the resulted array (**Figure 33**). The direction of main beam in measurement can track the simulated results. However, when phase shift is tuned, due to variation of electrical length change, and the amplitude variation on both WPD and RTPS causes the difference between direction of main beam in measurement and simulation. Additionally, fabrication tolerance also produces the beam angle error between the measured and calculated value. The measured beam scan angles are within 5° tolerance (**Table 1**). In general, the measurement results are in good agreement with the simulated results.

**Figure 31.**

**Figure 32.**

**127**

*Array antenna measurement in anechoic chamber.*

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

*Beamforming Phased Array Antenna toward Indoor Positioning Applications*

*Radiation pattern of microstrip patch antenna element.*

*Beamforming Phased Array Antenna toward Indoor Positioning Applications DOI: http://dx.doi.org/10.5772/intechopen.93133*

**Figure 31.** *Array antenna measurement in anechoic chamber.*

**4.2 Beamforming antenna measurement evaluation**

In general, the radiation pattern of an antenna is three-dimensional. Because it is impractical to measure a three-dimensional pattern, a number of two-dimensional patterns are measured. Patterns can be obtained by fixing one of angles (θ or ϕ) while varying the other. For a single antenna, the θ = π/2 azimuthal pattern and ϕ = 0 elevation pattern are usually chosen. For phased array antenna, only θ = π/2 azimuthal pattern is measured to observe the direction of main beam, and the ϕ = 0 elevation pattern does not provide useful information. Ideally, the measurement system would be placed in outdoor space in the far field region to cancel reflection waves. However, this ideal condition is not achievable; therefore indoor anechoic chambers have been developed for this antenna array measurement. The region inside anechoic chambers is covered with RF absorber. The reflection coefficient of

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

Structure of the measurement room is shown in **Figure 30**. A horn antenna, HF 906, is used as a transmitting antenna, and antenna under test (AUT) is received antenna. Thanks to the reciprocity property of antennas, the transmitting and receiving radiation patterns are identical. Therefore, the swap between two antennas is not necessary. The receiving and transmitting powers are measured by the PNA N5222A network analyzer in which the AUT is rotated through a rotating table. To automatically operate this system, a rotating table with an angle step of 5° is set up, and then the measured results are extracted and analyzed from the

**Figure 31** shows the radiation pattern of my microstrip patch antenna. We can see that the half power beam width is larger than 90° and the measured radiation pattern is similar to simulated one. Therefore, in terms of radiation pattern, each antenna element meets the requirement for indoor positioning system (**Figure 32**).

All components of the array including power divider, phase shifter, antenna, and controller are assembled together to form a phased array antenna. The radiation

*4.2.1 Material and facility preparation*

anechoic chambers is about 40 dB [15, 37].

*4.2.2 Beamforming array measurement*

*Anechoic chamber configuration for measuring beamforming antenna array.*

network analyzer.

**Figure 30.**

**126**

**Figure 32.** *Radiation pattern of microstrip patch antenna element.*

patterns of phased array antenna are also measured in anechoic chamber at General Department of Technical Logistics of the Vietnamese Ministry of Public Security, similar to microstrip patch antenna at 2.45 GHz. The phased array antenna will be mounted in the rotating table to steer the main beam toward angles from 45 to 45° with step of 5°. The measured results are compared with simulated results in same coordinate to investigate the quality of the resulted array (**Figure 33**). The direction of main beam in measurement can track the simulated results. However, when phase shift is tuned, due to variation of electrical length change, and the amplitude variation on both WPD and RTPS causes the difference between direction of main beam in measurement and simulation. Additionally, fabrication tolerance also produces the beam angle error between the measured and calculated value. The measured beam scan angles are within 5° tolerance (**Table 1**). In general, the measurement results are in good agreement with the simulated results.

**129**

*Beamforming Phased Array Antenna toward Indoor Positioning Applications*

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

### *Beamforming Phased Array Antenna toward Indoor Positioning Applications DOI: http://dx.doi.org/10.5772/intechopen.93133*

**128**

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

**Figure 33.**

*Radiation pattern of phased array antenna at different angles.*

Regarding side lobes, compared with simulated results, the gain of side lobes in reality is much higher. The reason is due to the difference of space in simulation and measurement. In simulation, the array antenna is computed in open space, and as a result, there is no affection of reflection on radiation pattern. In reality, although the antenna array is measured in an anechoic chamber, the reflection from wall and other objects in chamber still exist and affect to measured results. Compared with main lobe, side lobe level is less than about 10 dB in most case (**Figure 33**).

A comparison about performance among my antenna design with previous antenna designs for indoor localization is presented in **Table 2**. It can be seen that, in previous designs, based on switching predefined beams, the number of beam is similar to the number of antenna elements. This leads to the limitation of the number of lobes due to the size of an indoor antenna that cannot be too large. Hence, the scan step of these design is quite large, namely 60, 30, 90, and 18° corresponding to researches [10–13]. In this antenna array, by controlling the array factor of array antenna through phase shifter controlling of wave coming to antennas, the number of beam does not depend on the number of antenna element. Simultaneously, the full 360° continuous phase shifter enables me to arbitrarily adjust the phase shift, so the main beam can be steered continuously. The resolution of scanning angle step in steering can be achieved at 5°.

**5. Conclusion**

**Table 1.**

**Table 2.**

**131**

With the desire to improve the resolution of AoA-based indoor positioning system, this chapter has focused on the design of multi-port phased array antenna

**Antenna Scanning range No. of beam Average step No. of antenna** [10] 360° 6 60° 6 [11] 360° 12 30° 13 [12] 360° 4 90° 5 [13] 73° 4 18° 4 **This work 90**° **19 5**° **8**

**Main beam angle Simulated side lobe level Measured side lobe level**

0° 13 dB 11 dB 5° 12 dB 10 dB 10° 12 dB 10 dB 15° 15 dB 9 dB 20° 14 dB 10 dB 25° 11 dB 10 dB 30° 11 dB 8 dB 35° 11 dB 10 dB 40° 11 dB 10 dB 45° 13 dB 12 dB 5° 12 dB 10 dB 10° 12 dB 10 dB 15° 15 dB 9 dB 20° 14 dB 9 dB 25° 11 dB 9 dB 30° 11 dB 9 dB 35° 11 dB 10 dB 40° 11 dB 10 dB 45° 13 dB 8 dB

*Beamforming Phased Array Antenna toward Indoor Positioning Applications*

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

beamforming array antenna with two-way Wilkinson power divider that is able to limit the loss and increase the isolation between the output ports. In addition, the important part in the array, the reflection type phase shifter, can continuously control the phase shift in full 360**°** range with low insertion loss and small variation. The main beam of the array antenna can be steered in direction from 45 to 45°

using the reflection type phase shifter. The studies demonstrate that the

*Comparison with previously studied beamforming array antenna designs for indoor localization.*

*Comparison between simulated and measured main beam angle and side lobe level.*


#### *Beamforming Phased Array Antenna toward Indoor Positioning Applications DOI: http://dx.doi.org/10.5772/intechopen.93133*

**Table 1.**

*Comparison between simulated and measured main beam angle and side lobe level.*


**Table 2.**

Regarding side lobes, compared with simulated results, the gain of side lobes in reality is much higher. The reason is due to the difference of space in simulation and measurement. In simulation, the array antenna is computed in open space, and as a result, there is no affection of reflection on radiation pattern. In reality, although the antenna array is measured in an anechoic chamber, the reflection from wall and other objects in chamber still exist and affect to measured results. Compared with main lobe, side lobe level is less than about 10 dB in most case

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

A comparison about performance among my antenna design with previous antenna designs for indoor localization is presented in **Table 2**. It can be seen that, in previous designs, based on switching predefined beams, the number of beam is similar to the number of antenna elements. This leads to the limitation of the number of lobes due to the size of an indoor antenna that cannot be too large. Hence, the scan step of these design is quite large, namely 60, 30, 90, and 18° corresponding to researches [10–13]. In this antenna array, by controlling the array factor of array antenna through phase shifter controlling of wave coming to antennas, the number of beam does not depend on the number of antenna element. Simultaneously, the full 360° continuous phase shifter enables me to arbitrarily adjust the phase shift, so the main beam can be steered continuously. The resolution

of scanning angle step in steering can be achieved at 5°.

*Radiation pattern of phased array antenna at different angles.*

(**Figure 33**).

**130**

**Figure 33.**

*Comparison with previously studied beamforming array antenna designs for indoor localization.*
