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Single Patch Antenna And Array Antenna Computer Science Essay

This paper presents the design of Single Rectangular Patch Antenna and Rectangular Patch Array Antenna at frequency of 2.5GHz. The gain of Patch Antenna can be increased by using the Array technique. The designed antenna is simulated by using CST Studio Suite 2010: Microwave Studio software.

NOWADAYS, the large demand by end user for integrated wireless digital application has increased the use of microstrip antenna. The microstrip antenna is preferred due to its low profile, light weight and low volume [1]. Microstip antennas are widely used for commercial applications such as direct broadcast satellite communication (DBS), Global Positioning System (GPS) and remote sensing applications. With its small size and high density packaging advantages, the microstrip technology is suitable for RFICs (Radio Frequency Integrated Circuits) and MMICs (Microwave Monolithic Integrated Circuits).

However, it has its disadvantages of surface waves generation, mutual coupling, coupling with other components, narrow bandwidth, loss due to feed mechanism, low efficiency, low power rating, spurious radiations, higher side lobes and low scanning abilities [1]. In order to overcome the issues of gain that faced by microstip antenna, array technique is used. Patch Array Antenna is design to archive higher gain than Single Patch Antenna which shown in Figure 1. It is on the concept of the larger the number of antenna elements, the better the gain of antenna array is due to its electrical size. Thus, in this paper, the gain of a Single Patch Antenna is improved by using Patch Array Antenna.

ANTENNA DESIGN

Single Rectangular Patch Antenna

Since

W

yo

Lact

Figure 1: Single Patch Antenna

Rectangular Patch Array Antenna

100Ω

70.71Ω

50Ω

50Ω

70.71Ω

100Ω

50Ω

Figure 2: Array Patch Antenna

The same equation was used when calculating the dimension of the array antenna. The feed line of array antenna was calculated by using the quarter wave transformer method.

SIMULATION

Rectangular Single Patch Antenna

Figure 3: Return Loss for Single Patch Antenna

By referring to Figure 3, the return loss for the rectangular single patch antenna is -43.6446dB at 2.5GHz.

Figure 4: Radiation Pattern

From Figure 4, HPBW = 93°, FNBW = 268°

Figure 5: Simulated Gain

Simulated gain for the single patch antenna = 3.385dB

Simulated directivity = 6.692dBi

Rectangular Array Antenna

Figure 6: Return Loss for Array Patch Antenna

From Figure 6, the return loss for the array patch antenna is -16.30616dB at 2.5GHz.

Figure 7: Radiation Pattern

From Figure 7, HPBW = 65°, FNBW = 299°

Figure 8: Simulated Gain

Simulated gain for array patch antenna = 5.936dB

Simulated directivity = 9.767dBi

MEASUREMENT

Single Patch Antenna

Figure 9: Measured Return Loss

The attenuation of network analyzer = 0.42dB

Return loss = -24.647dB at 2.708GHz

Table 1: Power Received by the Single Patch Antenna

Angle (°)

Power (dBm)

0

-35.99

30

-37.88

60

-42.46

90

-50.70

120

-55.12

150

-50.96

180

-48.71

210

-52.02

240

-58.88

270

-49.75

300

-43.09

330

-38.69

360

-35.99

By referring to Figure 10,

HPBW= 70°, FNBW=240°

Directivity = 22.89dB at the angle of 240°

To calculate the gain for single patch antenna,

From spectrum analyzer,

Figure 10: Measured Radiation Pattern

Array Patch Antenna

Figure 11: Measured Return Loss

The attenuation of network analyzer = 0.42dB

Return loss = -13.917dB at 2.758GHz

Table 1: Power Received by the Patch Array Antenna

Angle (°)

Power (dBm)

0

-36.76

30

-42.39

60

-77.98

90

-56.17

120

-50.36

150

-49.83

180

-52.80

210

-51.24

240

-48.68

270

-52.69

300

-56.03

330

-44.37

360

-36.76

Figure 12: Measured Radiation Pattern

By referring to Figure 12,

HPBW = 36°, FNBW = 87°

Directivity = 41.22dB at the angle of 60°

To calculate the gain for single patch antenna,

From spectrum analyzer,

DISCUSSION

In Table 3 below, we observed the comparison between the simulation and measurement results of the antenna parameters for the single and array patch antenna. The antenna parameters that will be analyzed and discussed are return loss (S11), receiver gain (GR), directivity (D), HPBW and FNBW.

Table 3: Comparison between simulation and measurement

for single and array patch antenna

Antenna Parameters

Simulation

Measurement

Single patch

Array patch

Single patch

Array patch

S11

(dB)

-43.65 at 2.5GHz

-16.31 at 2.5GHz

-24.27 at 2.708GHz

-14.10 at 2.758GHz

GR

3.385dB at 2.5GHz

5.936dB at 2.5GHz

2.667dB at 2.69GHz

1.325dB at 2.80GHz

D

9.392dB

12.46dB

22.89dB at 240°

41.22dB at 60°

HPBW

93°

65°

70°

36°

FNBW

268°

299°

240°

87°

From Figure 3 and Figure 6, the designed single patch antenna and array patch antenna have a return loss of -43.6446dB and -16.30616dB at 2.5GHz respectively, whereby both return loss are less than -10dB. This means that the electromagnetic wave being transmitted is more than 90% of injected signal. In other word, there is less than 10% of signal being reflected due to mismatch. The designed single patch antenna and array patch antenna have 99.99% and 97.52% of efficiency respectively. When the return loss of an antenna is close to -∞dB, the antenna will have better efficiency.

The simulated gain for single patch antenna is 3.385dB while the simulated gain for array patch antenna is 5.936dB; there is 2.551dB increase in the gain with array method. Besides, the radiation patterns also show that the directivity for array patch antenna is better than the single patch antenna. The simulated directivity for single patch antenna is 6.692dBi while for array patch antenna is 9.767dBi, which show an increase of 3.075dBi in directivity.

In the measurement, we could observe that the measured gain in the array antenna is 50.32% lesser than that of single patch antenna as shown in Table 3. Theoretically, the gain of the array patch antenna should be higher than that of single patch. This is because the array method can increase the gain of the single patch. However, the measurement shows that the gain of the single patch is not increased in the array patch compared to the simulation result whereby the gain for the array patch antenna is higher than the single patch. The measurement for the gain in the single and array patch is taken at different center frequencies, 2.69GHz and 2.80GHz than the defined center frequency of 2.5GHz. The improper settings of the specifications of FR4 board in the simulation and flaws during the fabrication could have caused the center frequency to shift about 0.1~0.3GHz. Other than that, imperfect coupling between antenna and cable could have caused the power received by the array patch antenna to be lower than that of single patch because the received power will affect the gain of the receiver.

For measurement part, the measured return loss for single patch antenna is -24.474dB at 2.708GHz while the return loss for array patch antenna is -14.097dB at 2.758GHz. There are a slightly frequency shifting in both return loss which is about 0.2GHz. These results may be caused by the improper fabrication procedure and also due to the oxidation happened to the surface of the single and array patch antenna.

For the single patch, we could see the comparison between the simulation and measurement results from Figure 4 and 10. The measured HPBW and FNBW in Figure 10 are 24.73% and 10.45% lower than that of simulation. As for the directivity of the single patch, we observed that the measured directivity is 13.50dB higher than the simulated directivity of 9.392dB as shown in Table 3. The gain obtained from measurement is 21.21% lower than that of simulation. The shifting of the center frequency from 2.5 GHz to 2.69GHz may have caused the differences in the HPBW, FNBW, directivity and gain in the single patch.

For the array patch antenna, the measured gain is 1.325dB at center frequency, 2.80GHz which is 77.68% lower than that of simulation as shown in Table 3. Furthermore, there is a difference of 28.76dB in directivity of the array whereby the measured directivity is higher than the simulation result. The measured HPBW is 44.62% lower than the simulated HPBW, 65°. For the FNBW, the measured angle is smaller compared to simulation whereby its angle is 87° and the difference between simulation and measurement is 70.90%.

CONCLUSION

In this report, the single and array patch antennas have been designed, simulated, fabricated and measured. The performance of both the single and array patch are observed and analyzed in terms of gain, directivity, HPBW and FNBW. The array patch has shown improvements in terms increased directivity and narrower HPBW and FNBW compared to the single patch at frequency 2.758GHz. However, the gain of array patch is not increased compared to the gain of the single patch. This is due to the shifting of the centre frequency about 0.2GHz from the defined frequency of 2.5GHz. The gain of the single patch antenna can be improved by using array method but using more than two patch elements. A higher gain and directivity can be achieved by increasing the number of patch elements.

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