I Shaped Array Of Mimo Antenna

Published Date: 02 Nov 2017

ABSTRACT:

In this paper, a new compact design of I-shaped array of MIMO antenna is implemented with the help of rectangular microstrip patch antenna. In today’s world antenna plays an important role in wireless areas such as base stations, antenna arrays, hand-held devices etc., Even though it has many applications there are some interference in the signal. To overcome that disadvantage a microstrip patch antenna is implemented with RT Duroid as a substrate material due to its benefits such as low loss, less expensive and low fabrication cost while each patch has individual substrate and ground which leads to low correlation and less interference. The proposed I-shaped array of antenna is designed successfully in Ansoft HFSS software over a multi-band operating frequency range of 6.9GHz, 10.6GHz and 13GHz. The antenna parameters are analyzed such as return loss is about -28.48dB, Isolation loss is about -40.8dB, VSWR range is 1.1, gain and directivity is about 2.66 dB and 2.79dB respectively. From this, the efficiency has been calculated as 95%. The main advantage of this paper is low correlation, less interference and is applicable for medical applications when it can be designed with respect to skin effect.

Keywords: Return Loss (RL), Isolation Loss (IL), Multiple-input-Multiple-Output (MIMO), High Frequency Structure Simulator (HFSS), Voltage Standing Wave Ratio (VSWR).

1. INRODUCTION:

In today’s world, wireless applications has a major role especially in wireless communication systems. For this application there is a need of an array of antenna to transmit and receive the multi-path propagation signal with high isolation, less mutual coupling and low interference[ ]. So, in this paper, we have introduced a new compact design of an I-shaped array of antenna with high isolation loss, return loss and good transmission efficiency. Since it is array of

antenna which has multiple number of antennas in transmitter as well as in receiver, it can also be called as Multiple-input and Multiple-output (MIMO) antenna. Section I deals about the MIMO antenna with its functions and advantages. Section II and III describes about the proposed antenna design with their antenna parameter calculations and results and discussions obtained by using HFSS software respectively. Section IV and V tells about the applications of this MIMO antenna and Conclusion respectively. Finally, Section VI and VII details about the acknowledgement and references.

1.1 MIMO antenna:

The communication performance can be improved by placing the multiple antennas at both the transmitter and receiver[ ]. This smart technology offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. Since it spreads same total transmit power over the antennas, it achieves array gain which improves the spectral efficiency and link reliability (reduced fading)[ ]. From the above properties, it has wonderful attracted attention in wireless communication standards such as IEEE 802.11n (Wi-Fi), 4G, 3GPP Long Term Evolution, WiMAX and HSPA[ ].

1.2 Functions of MIMO antenna:

The three main functions of MIMO are as follows [ ]:

Pre-coding: In beam forming, the signal power gets maximized at the receiver when the signal from each transmitter antennas has appropriate phase. By adding the signals from different antennas, beam forming increases the received signal gain and reduces the multipath fading effect. Whereas for the receiver case, the transmit beam forming cannot maximize the signal level. In that case, pre-coding technique with multiple streams is used. It needs the transmit channel information.

Spatial multiplexing: Here a high rate signal gets split into multiple lower rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with different spatial signatures, the receiver can separate these streams into parallel channels. The main advantage of this technique is to increase the channel capacity at higher SNR, can be used with or without transmit channel knowledge. The maximum number of spatial streams is limited by the lesser of the number of antennas at the transmitter or receiver. It can also be combined with pre-coding when the channel is known at the transmitter.

Diversity Coding: This technique is used when there is no channel knowledge at the transmitter. It exploits the independent fading in the multiple antenna links to enhance signal diversity. Spatial multiplexing can also be combined with diversity coding when decoding reliability is in trade-off.

1.3 Advantages of MIMO antenna:

It takes several advantages such as multi-path, delivers simultaneous speed, coverage and reliability improvements [ ]. Even though it utilizes multiple antennas to send multiple parallel signals (from transmitter), these signals will bounce off trees, buildings etc., in an urban environment and get continued on either way to reach the receiver or destination in different directions. In the same time, when there is a need to sort out the multiple signals into one signal which has the originally transmitted data, the receiver end has to use some algorithm or signal processing techniques [ ].

2. PROPOSED ANTENNA DESIGN:

We have chosen the I-shaped array of microstrip antenna which is designed in the HFSS software where as the important parameters of antenna has been analyzed and the results are shown below.

Figure 1: Proposed I-shaped array of antenna in HFSS software

The proposed I-shaped array antenna is made up with the substrate material as RT Duroid which has the dielectric constant of 2.2 which leads to less complexity in fabrication and less expensive. The array of patch is designed with equal distance according to the lambda calculation. The main advantage of this antenna is that it has low interference and low correlation since each patch has individual substrate and ground. So the correlation between the channel is lower. Another main advantage is that the antenna operates in a multi-band frequency such as 6.9GHz, 10.6GHz and 13GHz.

2.1 Calculation of I-shaped antenna:

Given relative permittivity εr, height of the substrate and the operating frequency the design of the microstrip patch proceeds as follows.

Finding the width of the patch:

W= ------ (1)

Here c is speed of light and is the resonant frequency

Finding the effective dielectric constant:

----- (2)

Taking into account the fringing effect:

The fringing fields along the width of the structure are taken as radiating slots and the patch antenna is electrically seen to be a bit larger than its physical size (Balanis.C, 2009).

----- (3)

Calculating the effective length of the patch

----- (4)

Calculating the actual length of the patch

------ (5)

W, L, h, fr, Ɛr, Ɛeff, C are width of patch, length of patch, height of substrate, resonant frequency, dielectric constant of substrate, effective dielectric constant of substrate and speed of light in the vacuum respectively (Balanis.C, 2009).

Calculating the ground plane dimensions:

Size of the ground plane should be greater than the patch dimensions by approximately six times or twelve times the substrate thickness so that results are similar to the one using infinite ground plane. From the above length and width equations, the width and length of the ground plane are determined.

------ (6)

------ (7)

Lg, Wg, Lf are length of ground plane, width of ground plane, and length of feed in (6) and (7) respectively. By using these formulas the values have been found which is prescribed in the following Table 1:

Table 1:

PARAMETRS

SYMBOL

VALUES

Dielectric Constant of the Substrate

εr

2.2

Height of the dielectric substrate

1.6 mm

Operating frequency

6.9 GHz, 10.6 GHz, 13GHz

Width of the substrate

Ws

39.6 mm

Length of the substrate

Ls

29.6 mm

Width of the ground

Wg

39.6 mm

Length of the ground

Lg

29.6 mm

Length of the patch

Lp

20 mm

Width of the patch

Wp

30mm

3. SIMULATION RESULTS AND DISCUSSIONS:

In this section, it deals about the antenna parameters such as return loss, VSWR, gain, directivity and isolation loss. A good MIMO antenna should have high isolation loss between the transmitter and receiver and mutual coupling. For a proposed I-shaped array of antenna the return loss (RL should be high for good antenna) is about -28.48dB, -19.14dB, -13.62dB at 6.9GHz, 10.6GHz and 13GHz respectively which is shown below.

5.00

7.50

10.00

12.50

15.00

Freq [GHz]

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

dB(S(1,1))

HFSSDesign1

XY Plot 1

ANSOFT

m2

m3

m4

m1

Curve Info

dB(S(1,1))

Setup1 : Sweep

Name

X

Y

m1

6.9700

-28.4806

m2

10.5900

-19.2395

m3

13.1700

-13.7063

m4

14.1000

-11.9019

Figure 2: RL of I-shaped array antenna

The VSWR of this antenna is less than 2 (VSWR<2). It is about 1.1 and 1.2 at 6.9GHz and 10.6GHz respectively. The plot is shown below:

5.00

7.50

10.00

12.50

15.00

Freq [GHz]

0.00

2.50

5.00

7.50

10.00

12.50

15.00

abs(VSWR(1))

HFSSDesign1

XY Plot 2

ANSOFT

m2

m1

Curve Info

abs(VSWR(1))

Setup1 : Sweep

Name

X

Y

m1

6.9700

1.0783

m2

10.5900

1.2450

Figure3: VSWR plot of I-shaped array antenna

The gain of this beautiful antenna is about 2.7dB at theta equals to 0 degree at 6.9GHz.

-15.00

-10.00

-5.00

0.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

HFSSDesign1

Radiation Pattern 1

ANSOFT

m1

Curve Info

dB(GainTotal)

Setup1 : LastAdaptive

Freq='4.81GHz' Phi='0deg'

Name

Theta

Ang

Mag

m1

0.0000

0.0000

2.6694

Figure 4: Gain of I-shaped array antenna

-200.00

-150.00

-100.00

-50.00

0.00

50.00

100.00

150.00

200.00

Theta [deg]

-20.00

-15.00

-10.00

-5.00

0.00

5.00

dB(GainTotal)

HFSSDesign1

XY Plot 5

ANSOFT

m1

Curve Info

dB(GainTotal)

Setup1 : LastAdaptive

Freq='4.81GHz' Phi='0deg'

dB(GainTotal)

Setup1 : LastAdaptive

Freq='4.81GHz' Phi='90deg'

Name

X

Y

m1

0.0000

2.6694

Figure 5: Gain in rectangular plot

Figure 6: Gain in 3D polar plot

The directivity of the proposed antenna is about 2.79dB at theta equals to 0 degree at 6.9GHz.

-15.00

-10.00

-5.00

0.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

HFSSDesign1

Radiation Pattern 2

ANSOFT

m1

Curve Info

dB(DirTotal)

Setup1 : LastAdaptive

Freq='4.81GHz' Phi='0deg'

Name

Theta

Ang

Mag

m1

0.0000

0.0000

2.7973

Figure 7: Directivity of I-shaped array antenna

Isolation loss is the main parameter for the proposed antenna. Here it is about -40.8dB at 6.9GHz. The plot is shown below:

5.00

7.50

10.00

12.50

15.00

Freq [GHz]

-55.00

-50.00

-45.00

-40.00

-35.00

-30.00

-25.00

-20.00

-15.00

-10.00

dB(S(3,4))

HFSSDesign1

XY Plot 3

ANSOFT

m1

Curve Info

dB(S(3,4))

Setup1 : Sweep

Name

X

Y

m1

6.9700

-40.8309

Figure 8: isolation loss of the proposed antenna

4. APPLICATIONS:

This MIMO antenna has been applied for wireless applications such as WLAN, WIMAX, Wi-Fi, GSM and Bluetooth with low interference. By doing modification in this antenna with respect to skin effect, it can be applied to medical applications such as breast cancer detection and tumor diagnosis.

5. CONCLUSION:

Thus we conclude that a new modified I-shaped array antenna is designed over a multi-band frequency in Ansoft HFSS software successfully. The antenna parameter such as RL is about -28.48dB, -19.14dB, -13.62dB at 6.9GHz, 10.6GHz and 13GHz respectively. The IL is obtained about -40.8dB, -23.5dB at 6.9GHZ and 10.6GHZ respectively. The VSWR is less than 2 which is about 1.1 and 1.2. The gain and directivity is about 2.66dB and 2.79 dB respectively at 6.9GHz. The main advantage of this antenna is that it has low correlation between the channel, operating in a multi-band frequency and low interference.

6. ACKNOWLEDGEMENT:

We express our gratitude to each of our faculties and friends for their timely help. Finally, We are very grateful to our family members and friends who endorsed us with content encouragement and help through the project.