*4.1.1 Wilkinson power divider (WPD)*

In the two-wayWPD, theoretically, the total input power is equally divided into two output ports. Assume that the input port is port 1 and the output ports are port 2 and 3, the transmission coefficient S21 = S31 = 3dB as shown in **Figure 18b**.

However, microstrip circuits on any substrate are affected by the loss tangent coefficient of the substrate and the microstrip discontinuities. The loss tangent represents the loss in the dielectric. The higher the loss tangent is, the more the loss is. For FR4 substrate, the loss tangent is about 0.025, so the forward gain of WPD on FR4 is less than theoretical one. Furthermore, the microstrip discontinuity phenomenon, as well as [22, 34, 35], appears in practice and generates parasitic

**Figure 18.** *The simulated 2-way WPD: (a) schematic circuit; (b) forward gains S21, S31.*

width *W* and length *L* are computed with the following Equation [15, 32, 33] where

r

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

ffiffiffiffiffiffiffiffiffiffi 2 *ε* þ 1

�

2

with *Leff* is the effective length, *ΔL* is the length adjustment, *εeff* is the effective

To validate the design of the antenna, every component in the phased array structure is evaluated and measured. All the simulations are performed on Keysight Technologies's Advanced Design System (ADS) software and CST Microwave Studio. All the components are fabricated on the FR4 substrate with dielectric constant ε of 4.3, loss tangent tanδ of 0.02, substrate thickness h of 62 mil (1.58 mm), and the

*W*

*<sup>h</sup>* <sup>þ</sup> <sup>0</sup>*:*<sup>264</sup> *W <sup>h</sup>* <sup>þ</sup> <sup>0</sup>*:*<sup>8</sup>

¼ 3*:*9953

¼ 36*:*60 *mm* (30)

¼ 0*:*73 *mm*

*L* ¼ *Leff* � 2 � *ΔL* ¼ 28*:*07 *mm* (31)

*<sup>W</sup>* <sup>¼</sup> <sup>3</sup> � <sup>1011</sup> 2 � *f*

f is center frequency (2.45 GHz):

*Block diagram of varactor diode controller.*

*Leff* <sup>¼</sup> <sup>3</sup> � <sup>10</sup><sup>11</sup>

*<sup>ε</sup>eff* <sup>¼</sup> *<sup>ε</sup>* <sup>þ</sup> <sup>1</sup>

2 � *f* � ffiffiffiffiffiffi

*<sup>Δ</sup><sup>L</sup>* <sup>¼</sup> <sup>0</sup>*:*<sup>412</sup> � *<sup>h</sup>* � *<sup>ε</sup>eff* <sup>þ</sup> <sup>0</sup>*:*<sup>3</sup>

<sup>2</sup> <sup>þ</sup> *<sup>ε</sup>* � <sup>1</sup> 2

permittivity, and *h* is the substrate thickness.

conductive copper thickness t of 1.4 mil (1 oz).

*εeff*

**4. Evaluation of phased array antenna performance**

<sup>p</sup> <sup>¼</sup> <sup>29</sup>*:*<sup>53</sup> *mm*

*εeff* � 0*:*258

<sup>1</sup> <sup>þ</sup> <sup>12</sup> *<sup>h</sup> W* � ��<sup>1</sup>

where

**116**

**Figure 17.**

8

>>>>>>>>>>>><

>>>>>>>>>>>>:

components, changing the parameters of circuit. Thus, in simulation, it is necessary to insert discontinuity components such as Bend and Tee so that the simulated results are close to measured results. After that, dimension of transmission lines is slightly adjusted by using optimization tool in ADS software in order to get the desired results. The two-way WPD is shown in **Figure 19** and S21 = S31 = 3.23 dB.

According to the cascade structure, the eight-way WPD is formed from the twoway WPDs and 50 Ω transmission lines. In addition, in microwave circuit, when transmission lines are placed closely to each other, the coupling between them occurs, which affects to characteristics of circuit. The coupling is an issue not easy to calculate and estimate and does not appear on schematic simulation, so the EM simulation and

Finally, the eight-way WPD is fabricated on FR4 substrate and then measured by PNA N5222A network analyzer. The forward gain for each port are shown in **Figure 21,** in which the thin red line, bold blue lines, and blue dash lines are forward gains of 8-way WPD in schematic simulation, EM co-simulation and fabrication, respectively. It can be seen that for schematic simulation, the forward gains in all output ports are identical and equal to 10.882 dB instead of 9 dB as in theory. The loss occurs during propagating on FR4 substrate with loss tangent coefficient tanδ = 0.025. For EM co-simulation, the forward gains at the output ports are not identical and change from 11.031 to 10.493 dB. As mentioned above, the difference comes from the coupling between transmission lines.

The forward gains of 8-way WPD made on FR4 material are relatively close to the simulation results in the schematic circuit and EM co-simulation at the designed frequency 2.45 GHz. The measurement results change around the simulation results with a difference less than 1 dB. The differences are due to the fabrication tolerance

Additionally, in **Figure 22,** the thin red line, thick blue line and dash blue line represent the schematic simulated result, electromagnetic co-simulation, and the measured result, respectively. The isolation between output ports of the power

For low loss variation, the important component – RTPS is designed on substrate

Roger4003C with dielectric constant ε of 3.55, loss tangent tanδ of 0.0021 and substrate thickness h of 0.8 mm. The RTPS structure is simulated on Advanced Design Systems ADS software. ADS has built-in components such as microstrip lines, terminals, DC voltage, and stubs; however, the selected SMV1247 varactors are not supported, hence it is necessary to create an equivalent model of SMV1247

before designing and simulating the RTPS. The C-V characteristic curve of SMV1247 with the ADS model at 100 MHz is shown in **Figure 23b**. This curve is

as well as the heterogeneity of the material in reality, causing the change of mismatch and loss compared with simulation. For the other frequency band, namely less than 2.4 GHz and greater than 2.5 GHz, there are large differences between simulation and reality. The reason is that the fabrication errors will make a great impact at undesired frequencies. However, this error does not affect the final

result because the system is designed to operate at 2.45 GHz.

divider is about 20 dB, similar to products on the market.

*4.1.2 Reflection type phase shifter*

**Figure 20.**

**119**

*Eight-way Wilkinson power divider.*

EM co-simulation are used to ensure the final simulated results (**Figure 20**).

*Beamforming Phased Array Antenna toward Indoor Positioning Applications*

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

#### **Figure 19.**

*The 2-way WPD: (a) schematic circuit; (b) forward gains S21, S31*.

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

According to the cascade structure, the eight-way WPD is formed from the twoway WPDs and 50 Ω transmission lines. In addition, in microwave circuit, when transmission lines are placed closely to each other, the coupling between them occurs, which affects to characteristics of circuit. The coupling is an issue not easy to calculate and estimate and does not appear on schematic simulation, so the EM simulation and EM co-simulation are used to ensure the final simulated results (**Figure 20**).

Finally, the eight-way WPD is fabricated on FR4 substrate and then measured by PNA N5222A network analyzer. The forward gain for each port are shown in **Figure 21,** in which the thin red line, bold blue lines, and blue dash lines are forward gains of 8-way WPD in schematic simulation, EM co-simulation and fabrication, respectively. It can be seen that for schematic simulation, the forward gains in all output ports are identical and equal to 10.882 dB instead of 9 dB as in theory. The loss occurs during propagating on FR4 substrate with loss tangent coefficient tanδ = 0.025. For EM co-simulation, the forward gains at the output ports are not identical and change from 11.031 to 10.493 dB. As mentioned above, the difference comes from the coupling between transmission lines.

The forward gains of 8-way WPD made on FR4 material are relatively close to the simulation results in the schematic circuit and EM co-simulation at the designed frequency 2.45 GHz. The measurement results change around the simulation results with a difference less than 1 dB. The differences are due to the fabrication tolerance as well as the heterogeneity of the material in reality, causing the change of mismatch and loss compared with simulation. For the other frequency band, namely less than 2.4 GHz and greater than 2.5 GHz, there are large differences between simulation and reality. The reason is that the fabrication errors will make a great impact at undesired frequencies. However, this error does not affect the final result because the system is designed to operate at 2.45 GHz.

Additionally, in **Figure 22,** the thin red line, thick blue line and dash blue line represent the schematic simulated result, electromagnetic co-simulation, and the measured result, respectively. The isolation between output ports of the power divider is about 20 dB, similar to products on the market.

### *4.1.2 Reflection type phase shifter*

For low loss variation, the important component – RTPS is designed on substrate Roger4003C with dielectric constant ε of 3.55, loss tangent tanδ of 0.0021 and substrate thickness h of 0.8 mm. The RTPS structure is simulated on Advanced Design Systems ADS software. ADS has built-in components such as microstrip lines, terminals, DC voltage, and stubs; however, the selected SMV1247 varactors are not supported, hence it is necessary to create an equivalent model of SMV1247 before designing and simulating the RTPS. The C-V characteristic curve of SMV1247 with the ADS model at 100 MHz is shown in **Figure 23b**. This curve is

**Figure 20.** *Eight-way Wilkinson power divider.*

components, changing the parameters of circuit. Thus, in simulation, it is necessary to insert discontinuity components such as Bend and Tee so that the simulated results are close to measured results. After that, dimension of transmission lines is slightly adjusted by using optimization tool in ADS software in order to get the desired results. The two-way WPD is shown in **Figure 19** and S21 = S31 = 3.23 dB.

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

**Figure 19.**

**118**

*The 2-way WPD: (a) schematic circuit; (b) forward gains S21, S31*.

**Figure 21.** *Forward gain from port 2–9 of the WPD.*

similar to the characteristic curve in the SMV1247 datasheet **Figure 23a**, so this SMV1247 model will be used on all ADS simulations. These characteristic curves were calculated from model in **Figure 24**.

model of SMV1247 is built with the Ls, Cp, and Rs values corresponding to SC-79

The RTPS is deployed both in schematic simulation and EM co-simulation to ensure the real operation (**Figure 25**). The microstrip discontinuity components such as bend, tee, and steps in width are inserted and their dimensions are adjusted in order to obtain the desired results. Then the RTPS is fabricated on Roger4003c (**Figure 26**) and measured by the Keysight PNA N5222A Network Analyzer. The results of the phase shifter are shown in **Figure 27**, where the green dash line, blue dash dot line, and red circle line are schematic simulation, EM

packages, Ls = 0.7nH, Cp = 0.54 pF, and Rs = 4.9 Ω (**Figure 24b**).

*Beamforming Phased Array Antenna toward Indoor Positioning Applications*

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

co-simulation, and measured results, respectively.

*C-V curve of SMV1247 on: (a) technical document [36]; (b) ADS.*

**Figure 22.**

**Figure 23.**

**121**

*Isolation between output ports.*

In the technical documentation of SMV1247, Skyworks provides the SPICE model (**Figure 24a**). After importing this model into ADS software, the equivalent *Beamforming Phased Array Antenna toward Indoor Positioning Applications DOI: http://dx.doi.org/10.5772/intechopen.93133*

**Figure 23.** *C-V curve of SMV1247 on: (a) technical document [36]; (b) ADS.*

model of SMV1247 is built with the Ls, Cp, and Rs values corresponding to SC-79 packages, Ls = 0.7nH, Cp = 0.54 pF, and Rs = 4.9 Ω (**Figure 24b**).

The RTPS is deployed both in schematic simulation and EM co-simulation to ensure the real operation (**Figure 25**). The microstrip discontinuity components such as bend, tee, and steps in width are inserted and their dimensions are adjusted in order to obtain the desired results. Then the RTPS is fabricated on Roger4003c (**Figure 26**) and measured by the Keysight PNA N5222A Network Analyzer.

The results of the phase shifter are shown in **Figure 27**, where the green dash line, blue dash dot line, and red circle line are schematic simulation, EM co-simulation, and measured results, respectively.

similar to the characteristic curve in the SMV1247 datasheet **Figure 23a**, so this SMV1247 model will be used on all ADS simulations. These characteristic curves

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

In the technical documentation of SMV1247, Skyworks provides the SPICE model (**Figure 24a**). After importing this model into ADS software, the equivalent

were calculated from model in **Figure 24**.

*Forward gain from port 2–9 of the WPD.*

**Figure 21.**

**120**

**Figure 24.** *Equivalent model of SMV1247: (a) on SPICE [36]; (b) on ADS.*

**Figure 27** shows the forward gains (S21) in all three cases simulating the schematic, electromagnetic field simulation, and measurement results. I find that the energy transmitted through the phase shifter is little less than that of the schematic and electromagnetic simulation. The reason may be due to the error in fabrication process as well as contact between the varactors and the microstrip line, which is

**Figure 25.**

**123**

*Schematic circuit of reflection type phase shifter on ADS.*

*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*

**Figure 25.** *Schematic circuit of reflection type phase shifter on ADS.*

**Figure 27** shows the forward gains (S21) in all three cases simulating the schematic, electromagnetic field simulation, and measurement results. I find that the energy transmitted through the phase shifter is little less than that of the schematic and electromagnetic simulation. The reason may be due to the error in fabrication process as well as contact between the varactors and the microstrip line, which is

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

*Equivalent model of SMV1247: (a) on SPICE [36]; (b) on ADS.*

**Figure 24.**

**122**

**Figure 26.** *Reflection type phase shifter fabricated on Roger4003c.*

respectively. The VSWR and S11 of patch antenna versus frequency are shown in **Figure 29**, where the thin red lines and dash blue lines are simulated and measured characteristics, respectively. It can be seen that in simulation, my microstrip patch antenna can operate at Wi-Fi band with resonant frequency from 2.4 to 2.484 GHz. However, due to the heterogeneity of the material in practice as well as errors in fabrication, my microstrip patch antenna in reality can only operate from 2.424 to 2.485 GHz. Although this antenna cannot be used in whole range of Wi-Fi band, it

*Beamforming Phased Array Antenna toward Indoor Positioning Applications*

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

can still operate at several channels of Wi-Fi.

*Microstrip patch antenna parameters: (a) VSWR; (b) return loss.*

**Figure 28.**

**Figure 29.**

**125**

*Fabricated microstrip patch antenna.*

**Figure 27.** *Transmission coefficient S21 of RTPS: (a) magnitude; (b) phase.*

not ideal and alter the resistance value in the equivalent circuit of the varactors and resulting in a loss of power that is much larger than simulation. The insertion loss is about 2.5 dB with nearly 0.5 dB of variation. The low insertion loss variation enables us to make a phased array antenna with uniform amplitude and spacing. **Figure 27b** shows phase shifts in three cases, the schematic, electromagnetic simulation, and measurement results. The phase shifters are capable of shifting about 370°. The phase shifter in reality although is not nearly as linear as the rest of the two cases, but with DAC12bits, the phase shifter can still be controlled with small resolution.

### *4.1.3 Microstrip patch antenna*

The fundamental part – microstrip patch antenna is simulated on CST Microwave Studio software and then fabricated on FR4 material, as shown **Figure 28**. In order to determine the bandwidth of an antenna, two parameters, VSWR and return loss S11, can be measured by the network analyzer PNA N5222A. At the operating frequency, the desired VSWR and S11 are less than 2 and 10 dB,

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

**Figure 28.** *Fabricated microstrip patch antenna.*

respectively. The VSWR and S11 of patch antenna versus frequency are shown in **Figure 29**, where the thin red lines and dash blue lines are simulated and measured characteristics, respectively. It can be seen that in simulation, my microstrip patch antenna can operate at Wi-Fi band with resonant frequency from 2.4 to 2.484 GHz. However, due to the heterogeneity of the material in practice as well as errors in fabrication, my microstrip patch antenna in reality can only operate from 2.424 to 2.485 GHz. Although this antenna cannot be used in whole range of Wi-Fi band, it can still operate at several channels of Wi-Fi.

**Figure 29.** *Microstrip patch antenna parameters: (a) VSWR; (b) return loss.*

not ideal and alter the resistance value in the equivalent circuit of the varactors and resulting in a loss of power that is much larger than simulation. The insertion loss is about 2.5 dB with nearly 0.5 dB of variation. The low insertion loss variation enables us to make a phased array antenna with uniform amplitude and spacing. **Figure 27b** shows phase shifts in three cases, the schematic, electromagnetic simulation, and measurement results. The phase shifters are capable of shifting about 370°. The phase shifter in reality although is not nearly as linear as the rest of the two cases, but with DAC12bits, the phase shifter can still be controlled with small

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

The fundamental part – microstrip patch antenna is simulated on CST Microwave Studio software and then fabricated on FR4 material, as shown **Figure 28**. In order to determine the bandwidth of an antenna, two parameters, VSWR and return loss S11, can be measured by the network analyzer PNA N5222A. At the operating frequency, the desired VSWR and S11 are less than 2 and 10 dB,

resolution.

**124**

**Figure 27.**

**Figure 26.**

*Reflection type phase shifter fabricated on Roger4003c.*

*Transmission coefficient S21 of RTPS: (a) magnitude; (b) phase.*

*4.1.3 Microstrip patch antenna*
