chapter 5 design and implementation of ...shodhganga.inflibnet.ac.in/bitstream/10603/28944/9/13...73...

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Chapter 5

DESIGN AND IMPLEMENTATION OF SWASTIKA-SHAPED

FREQUENCY RECONFIGURABLE ANTENNA ON FR4

SUBSTRATE

The same geometrical shape of the Swastika as developed in previous chapter

has been implemented on FR4 substrate in this chapter. The substrate is having

thickness of 1.6mm which is higher than the Rogers RO4350 used earlier in the thesis.

A thicker substrate, besides being mechanically strong, will increase the radiated

power, reduce conductor loss and improve impedance bandwidth. The FR4 epoxy

substrate used for the antenna design is having relative permittivity as 4.4 and

dielectric loss tangent of 0.02.

5.1 Parametric Study of Full Swastika-Shaped Microstrip Patch Antenna

The effect of variations in parameters of the frequency reconfigurable

Swastika-shaped patch antenna has been studied in this section. This study is different

than the study conducted in the last chapter. Here, only one parameter of the full

Swastika with a circle at the center (no gap in the design) has been varied and its

effect has been observed. To start with, the optimized parameters for a single layer

compact size Swastika-shaped frequency reconfigurable antenna for WLAN indoor

and outdoor applications are presented in Table 5.1. The study is based on simulations

only.

5.1.1 Study of Variation in the Radius of Center Circle (R)

In this section, the radius of center circle (R) has been varied around its

optimized value in the Swastika-shaped patch resonating at 5.8GHz without gaps in

the design. Three cases of R equals to 7.3mm, 7.4mm and 7.5mm are studied. The

return loss plots for this study are shown in Figure 5.1. It has been observed that the

increase in size of the center circle decreases the resonant frequency. For the

observation values, the change is not very significant. The reason behind this may be

the fact that the overall size of the patch is not changed. Hence, this parameter can be

used for fine tuning of the resonant frequency and impedance matching. Except for

74

the frequencies greater than 9GHz, all the three curves are almost same. The -10dB

bandwidths obtained in these cases are 125MHz.

Table 5.1 Parameters of the frequency reconfigurable Swastika-shaped antenna design

Parameter Optimized Value

Radius of center circle (R) 7.4 mm

Length of Horizontal & Vertical Stub (Lp and Wp) 32.4 mm

Length of Side Stub at 45 degree (Ls) 5 mm

Width of the Rectangular Sections (Wt) 2 mm

Diameter of four Dots (D) 4 mm

Co-ordinates of four Dots (xd, yd) (9,9),(9,-9),(-9,-9),(-9,9) mm

Feed Point radial distance at 45 degree from center 2.2 mm

Feed Point co-ordinates (xf, yf) (1.55563, 1.55563) mm

Ground size (Lg x Wg) 50 mm x 50 mm

Gap near circle for frequency reconfigurability 1 mm

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

Freq [GHz]

-30.00

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-15.00

-10.00

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Varying Radius 7.3(R),7.4(G),7.5(B))1

m1

m2

m3

Curve Info

7.3

7.4

7.5

Name X Y

m1 5.8150 -22.2959

m2 5.8150 -25.7744

m3 5.7700 -27.0788

Fig. 5.1 Return loss plots for study of radius of circle in full Swastika shape

75

5.1.2 Study of Variation in the Length of the Horizontal and Vertical Strips (Lp

and Wp)

In this section, all the parameters of full Swastika are same as shown in Table

5.1 except the Length of the horizontal and vertical Stubs (Lp and Wp) which has been

varied to observe the effect of overall dimension of the geometry. Three values

30.4mm, 32.4mm and 34.4mm are considered. A comparative return loss plots for

these values are presented in Figure 5.2. The results are again consistent with the

theory that increasing the overall size of the patch will decrease the resonant

frequency. The shapes of the curves are almost same except the left side shift with

increase in the size. The multiband response can be seen in the plots.

Fig. 5.2 Return loss plots for study of variation in the length of the horizontal and vertical strips

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

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Varying stub length 15.2(R),16.2(G),17.2(B)1

m1

m2

m3

Curve Info

30.4 mm

32.4 mm

34.4 mm

Name X Y

m1 6.0400 -23.0952

m2 5.8150 -25.7744

m3 5.5450 -21.9725

76

5.1.3 Study of Variation in Dot Location (±xd, ±yd)

In this section, the location of the dots, one dot in each quadrant in full

Swastika design is varied and the effect has been observed. All other parameters are

same as shown in Table 5.1. Four different values are considered as (±8mm, ±8mm),

(±8.5mm, ±8.5mm), (±9mm, ±9mm) and (±9.5mm, ±9.5mm). The return loss plots

for these values are shown in Figure 5.3. It has been noted that for first three values,

the curves are overlapping except very small change in the value of return loss at

some dips but for (±9.5mm, ±9.5mm), the resonant frequency has been changed

considerably. To further study the effect of dots in the geometry, a comparative graph

of return loss for presence and absence of dots has been presented in Figure 5.4. By

addition of dots in the design, the resonant frequency has been changed from 5.5GHz

to 5.8GHz. The effect is same as if the size of the patch is decreased to increase the

resonant frequency. In all the cases, the return loss is always better than -22dB. The

maximum return loss of -25.7dB has been obtained for (±9mm, ±9mm) case at

5.8GHz frequency. All the curves are showing multiband response. The first three

cases of the study are having other resonating frequencies higher than 5.8GHz

frequency and these are in the vicinity of 7.25GHz and 9.6GHz. For (±9.5mm,

±9.5mm) case, the other resonating frequencies are at 6.8GHz and near 10GHz. If not

required, these bands can be easily filtered out.

Fig. 5.3 Return loss plots for study of dot location

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

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Ansoft Corporation XY Plot 2

m1m2

m3

m4

Curve Info

8mm, 8mm

8.5mm,8.5mm

9.0mm,9.0mm

9.5mm,9.5mm

Name X Y

m1 5.8150 -22.9870

m2 5.8150 -22.7108

m3 5.8150 -25.7744

m4 5.5000 -22.5423

77

To further investigate the effect of addition and location of the dots, the E and

H field distribution of all the above mentioned cases are examined and shown in

Figure 5.5 and Figure 5.6 respectively. It has been clearly visible that the location of

dots affects the field distributions for both E and H. If Figure 5.5 (d) and (e) are

compared, it has been noticed that in without dot case, two stubs opposite to each

other are not having good field strength and if the dots are added, the electric field is

almost symmetrically distributed to all four stubs. Further, it has been seen that as the

dots move out, the field strength on the remaining patch is improved. It is happened

because when the dots are in proximity to the center circle, they are mutually coupled

to it and hence drawing the energy from the patch. When they are far from the circle,

this mutual coupling is weakened and now more energy is flown into the patch.

Similar is the case for H field distribution.

Fig. 5.4 A comparative return loss plots for without dot and with dot condition at ±9mm, ±9mm

locations

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

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)

Ansoft Corporation HFSSDesign1XY Plot 3

m1 m2

Name X Y

m1 5.5450 -25.6515

m2 5.8150 -25.7744

Curve Info

Without dots

With dots at 9mm, 9mm

78

(c) (d)

(e)

(a) (b)

Fig. 5.5 E-Field distribution on the Swastika geometries of different locations of dots

(a) 8mm, 8mm (b) 8.5mm, 8.5mm (c) 9mm, 9mm (d) 9.5mm, 9.5mm (e) No dot

79

(c) (d)

(e)

Fig. 5.6 H-Field distribution on the Swastika geometries of different locations of dots (a) 8mm, 8mm (b) 8.5mm, 8.5mm (c) 9mm, 9mm (d) 9.5mm, 9.5mm (e) No dot

(a) (b)

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The far field radiation patterns in E and H plane for without dot and with dots

at (±9mm, ±9mm) positions at their respective resonant frequency are shown in

Figure 5.7 (a) and (b) respectively. It has further been noted that apart from

symmetrical distribution of E and H fields due to the presence of dots in the Swastika

design, the maximum value of gain for Φ = 00 and 90

0 has been increased from

0.38dB to 0.95dB and from 0.98dB to 2.0dB respectively due to the presence of dots.

-3.80

-2.60

-1.40

-0.20

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

Ansoft Corporation HFSSDesign1Radiation Pattern 3

m1

m2

Curve Info

dB(GainTotal)

Freq='5.545GHz' Phi='0deg'

dB(GainTotal)


Name Theta Ang Mag

m1 -96.0000 -6.0000 0.3867

m2 -180.0000 -90.0000 0.9816

-5.60

-3.20

-0.80

1.60

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120


m1

m2

Curve Info

dB(GainTotal)


dB(GainTotal)


Name Theta Ang Mag

m1 -94.0000 -4.0000 0.9592

m2 -180.0000 -90.0000 2.0354

(a)

(b)

Figure 5.7 E and H plane radiation patterns (a) without dots at 5.5GHz (b) with

dots at ±9mm, ±9mm position at 5.8GHz

81

5.1.4 Study of Variation in Dot Diameter (D)

The size of the dot has been varied in this section while keeping their position

same. All the other parameters are same as given in Table 5.1 for full Swastika

design. Three values of diameter of dots as 3mm, 4mm and 5mm at (±9mm, ±9mm)

position in each quadrant are considered for the study. The return loss plots have been

shown in Figure 5.8. It has been observed that the variation in dot size doesn’t affect

the resonant frequency. The shape of the return loss curves for all the three cases are

exactly same up to 9GHz. Only small variation in the value of return loss at 5.8GHz is

seen in the plot.

5.1.5 Study of Variation in Length of the Side Stub (Ls)

The length of the side or end strip connected to each L-shaped section is

varied and the effect has been observed. Three values are considered as 4.5mm, 5mm

and 5.5mm. The angle of the side stub is 450 from the Y-axis. The return loss plots are

shown in Figure 5.9. The increase in length of the end strip increases the overall size

of the patch hence resonant frequency decreases. The resonant frequency

corresponding to 4.5mm, 5mm and 5.5mm are 5.86GHz, 5.81GHz and 5.72GHz

respectively. The shape of the curves is almost same for all the cases.

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

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turn

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)

Varying dot diameter 3(R),4(G),5(B)1

m1

m2

m3

Curve Info

3mm

4mm

5mm

Name X Y

m1 5.8150 -23.1667

m2 5.8150 -25.7744

m3 5.8150 -20.8043

Fig. 5.8 Return loss plots for variation in diameter of dots

82

5.1.6 Study of Angle of the Side Stub (θS)

The angle of the side or end stub connected to each L-shaped section has been

varied in this section of study. All the other parameters are same as mentioned in

Table 5.1. The angle is measured from Y-axis. Three values of the angle as 30 degree,

45 degree and 60 degree are considered. The return loss plots of these three values are

shown in Figure 5.10. As the angle increases, the resonant frequency also increases.

Hence, it can be concluded that the effect of increasing the angle of the side stub is

similar to the decrease in patch size so that the resonant frequency increases.

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-35.00

-30.00

-25.00

-20.00

-15.00

-10.00

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0.00R

etu

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Varying side stub length 4.5(R),5,5(G).5(B)1

m1

m2

m3

Curve Info

4.5mm

5.0mm

5.5mm

Name X Y

m1 5.8600 -34.5448

m2 5.8150 -25.7744

m3 5.7250 -21.2855

Fig. 5.9 Return loss plots for variation in length of side stub

83

5.1.7 Study of change in Feed Point in a Full Swastika Design

All the study of previous cases was carried out on a feed point that is located

at a distance of 2.2mm on a radial line which is at 45 degree in a quadrant. Due to

symmetry of the design, the feed point may be located in any of the quadrant at the

above mentioned point. The return loss plots for a feed point at the same line and a

distance of 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm and 2.4mm are shown in

Figure 5.11. It has been observed that the change in feed mainly affects the matching

of the antenna impedance and the feed. Better the matching, higher the return loss has

been obtained. For the first four cases, the resonant frequency is 5.77GHz and for

remaining three, it is 5.8GHz. For 5.77GHz resonant frequency, the return loss

improves continuously as the feed has been moved far from the center of the circle.

As soon as the feed is moved to 2.2mm, the resonant frequency has been changed to

5.8GHz with a return loss of -25.7dB. The return loss has been decreased at the same

resonant frequency if the feed point is moved farther. The feed point to be considered

finally for the antenna has been decided at 2.2mm on the same line.

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-35.00

-30.00

-25.00

-20.00

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-5.00

0.00

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dB

)

Varying stub angles 30(R),40(G),60(B)1

m1

m2

m3

Curve Info

30 degree

45 degree

60 degree

Name X Y

m1 5.7700 -19.8783

m2 5.8150 -25.7744

m3 5.8600 -31.3775

Fig. 5.10 Return loss plots for variation in angle of side stub

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5.1.8 Study of Size of Ground in a Full Swastika Design

In this section of study, the ground size has been varied and its effect has been

observed. Five square sizes of side length 45mm, 50mm, 55mm, 60mm and 65mm are

studied. The simulated return loss curves are shown in Figure 5.12. It has been

noticed that the size of ground doesn’t have major effect on resonant frequency but

impedance matching has been changed with the change in ground size. No effect on

shape of the radiation pattern has also been observed.

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-30.00

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-5.00

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)


m1m2

m3

m4

m5

m6

m7

Name X Y

m1 5.7700 -15.6920

m2 5.7700 -16.1762

m3 5.7700 -19.7634

m4 5.7700 -27.4928

m5 5.8150 -25.7744

m6 5.8150 -23.8599

m7 5.8150 -21.2437

Curve Info

1.8mm

1.9mm

2.0mm

2.1mm

2.2mm

2.3mm

2.4mm

Fig. 5.11 Return loss plots for variation in probe feed point

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-30.00

-25.00

-20.00

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-10.00

-5.00

0.00

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)


m1

m2

m3

m4

m5

Name X Y

m1 5.7700 -18.1855

m2 5.8150 -25.7744

m3 5.8150 -18.2671

m4 5.8150 -22.7842

m5 5.8150 -20.8283

Curve Info

45mm by 45mm

50mm by 50mm

55mm by 55mm

60mm by 60mm

65mm by 65mm

Fig. 5.12 Return loss plots for study of size of ground

85

5.1.9 Study of Length of Gap near Center Circle for Frequency

Reconfigurability

The gap between center circle and the four rectangular strips to create

frequency reconfigurability is primarily concerned with the size of the practical

switches to be placed in the gaps. The return loss plots for three gap sizes of 1mm,

1.5mm and 2mm are shown in Figure 5.13. It has been observed that the variation in

gap length doesn’t affect the resonant frequency but slightly changes the return loss.

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-35.00

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XY Plot 2

m1

m2

m3

Curve Info

1mm

1.5mm

2mm

Name X Y

m1 5.2300 -30.7936

m2 5.2300 -29.2360

m3 5.2300 -26.6693

Fig. 5.13 Return loss plots for study of variation in length of gap near circle

86

5.2 Frequency Reconfigurable Antenna Design

The parametric study of a single layer compact size frequency reconfigurable

antenna designed for WLAN indoor and outdoor services on Fr4 substrate of

thickness 1.6mm was presented in previous section. The study was conducted around

the optimized parameters presented in Table 5.1 for the required reconfigurability

between bands at 5.2GHz and 5.8GHz. The same parameters are used for simulations

of the antenna designs with all switches ON [96] and introducing frequency

reconfigurability by making all switches ON and OFF [97]. The two geometries are

shown in Figure 5.14. A small dot in the center circle is showing the feed point.

The simulated return loss plots for all switches ON and all switches OFF

conditions are shown in Figure 5.15. For all switches ON condition, the response is

multiband having resonant frequencies at 7.25GHz and 9.7GHz in addition to the

desired resonant frequency at 5.8GHz. If the higher frequency bands are not required,

they can be easily filtered out. If all the switches are OFF, the center circle is detached

from the four sections and the resonant frequency is moved to 5.2GHz. The effect of

creating gaps in the design is somewhat similar to the effect of increasing the patch

dimensions so that the resonant frequency decreases. The value of return loss obtained

at 5.2GHz is -30.7dB having lower -10dB frequency at 5.128GHz and higher -10dB

frequency at 5.323GHz resulting in 195MHz bandwidth. The simulated bandwidth is

marginally short from the bandwidth required for IEEE802.11a indoor services. A

Fig. 5.14 Antenna geometries representing (a) all switches ON (b) all switches OFF

(a) (b)

87

return loss of -25.7dB has been obtained at 5.8GHz frequency with lower -10dB

frequency at 5.742GHz and upper -10dB frequency at 5.868GHz resulting in 126MHz

bandwidth sufficient for IEEE802.11a indoor services. The reason of selecting full

patch to resonate at 5.8GHz and the patch with gaps to resonate at 5.2GHz is obvious

since the band at 5.8GHz has 125MHz bandwidth (5.725GHz-5.85GHz) and the band

at 5.2GHz has 200MHz bandwidth (5.15GHz-5.25GHz).

The VSWR curves for both the switching conditions are shown in Figure 5.16.

A VSWR value of 1.08 is obtained at 5.2GHz and at 5.8GHz, it is 1.05 showing good

matching of the antennas.

The E and H plane far field radiation patterns at 5.8GHz frequency for all

switches ON and at 5.23GHz frequency for all switches OFF condition are shown in

Figure 5.17. The E plane patterns for both the switching conditions are almost same in

shape and the direction of maximum radiation is also same except its magnitude. The

direction of maximum radiation for H plane has been changed but it has been

observed that the shapes of the patterns are not changed much at two different

frequencies.

The E and H field distributions along the patch surface in both the switching

conditions are presented in Figure 5.18 and Figure 5.19. It has been again observed

that not much energy is radiating through four dots for the similar reason discussed in

previous chapter. In Figure 5.18, it has been observed that the strength of electric field

at the sharp corners and bands is less in comparison to other areas whereas the

strength of magnetic field is lesser in the areas near to the dots. The effect of small

gaps of 1mm can be seen in Figure 5.19 as some energy has been observed in the

areas nearer to the circle due to mutual coupling.

Figure 5.20 shows the 3D polar plots for radiation patterns for without and

with gaps in the design. These are almost same in the shape. The Smith chart for

impedance variations of both the designs from 4GHz to 7GHz are shown in Figure

5.21. For full swastika without gap design, the antenna reactance is inductive at most

88

of the frequency points but at few points, it is capacitive also. In with gap design, the

antenna impedance is inductive throughout the observation frequency range.

The Gain v/s Frequency curves for both switching conditions for Φ = 00 and

900 values and at θ = 0

0 are shown in Figure 5.22. The curves for Φ = 0

0 and 90

0

values are exactly same for both the switching conditions. It has been observed that

gain has been obtained from nearly 4GHz to 9.6GHz frequency range in all switches

OFF condition whereas with all switches ON, the Gain has been observed in the

vicinity of 6GHz only.

The other parameters such as peak directivity, peak gain, and radiation

efficiency are shown in Table 5.2. The value of Axial Ratio is almost zero indicating

that it is a linearly polarized antenna.

Fig. 5.15 Simulated return loss plots for all switches OFF and all switches ON

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-35.00

-30.00

-25.00

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-15.00

-10.00

-5.00

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TU

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(d

B)


m1

m2

Curve Info

All Sw itches OFF

All Sw itches ON

Name X Y

m1 5.2300 -30.7936

m2 5.8150 -25.7744

5.20 5.30 5.40 5.50 5.60 5.70 5.80Freq [GHz]

5.00

10.00

15.00

20.00

VS

WR


1.0810 1.0529

9.6884

MX1: 5.2250

MX2: 5.8096

Curve Info

All Sw itches OFF

All Sw itches ON

Fig. 5.16 Simulated VSWR plots for all switches OFF and all switches

ON condition

89

Fig. 5.18 E-Field distribution on patch surface for (a) all switches ON (b) all switches OFF

(a) (b)

-1.60

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60

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Ansoft Corporation Radiation Pattern1

m1m2

Curve Info

dB(GainTotal)


dB(GainTotal)


Name Theta Ang Mag

m1 -94.0000 -4.0000 3.8538

m2 -92.0000 -2.0000 3.8436-5.60

-3.20

-0.80

1.60

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120


m2

m1

Name Theta Ang Mag

m1 -94.0000 -4.0000 0.9592

m2 -180.0000 -90.0000 2.0354

Curve Info

dB(GainTotal)


dB(GainTotal)


Fig. 5.17 E and H plane radiation patterns for (a) all switches ON (b) all switches OFF

(a) (b)

Fig. 5.19 H-Field distribution on patch surface for (a) all switches ON (b) all switches OFF

(b) (a)

90

Fig. 5.20 3D polar plots for (a) all switches ON (b) all switches OFF

(a) (b)

Fig. 5.22 Simulated Gain v/s Frequency curves for both conditions of switching

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-35.00

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5.00

Ga

inT

ota

l (d

B)


Curve Info

dB(GainTotal) All Sw itches OFF

Phi='0deg' Theta='0deg'

dB(GainTotal) All Sw itches OFF


dB(GainTotal) for All Sw ithes ON


dB(GainTotal) for All Sw ithes ON


5.002.001.000.500.20

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Ansoft Corporation HFSSDesign1Smith Plot 1

Curve Info

St(Cylinder2_1_1_1_T1,Cylinder2_1_1_1_T1)

Setup1 : Sw eep1

5.002.001.000.500.20

5.00

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-130

-120

-110-100 -90 -80

-70

-60

-50

-40

-30

-20

-10

Ansoft Corporation HFSSDesign1Smith Plot 1

Curve Info

St(Cylinder2_1_1_1_T1,Cylinder2_1_1_1_T1)

Setup1 : Sw eep1

Fig. 5.21 Smith charts for 4-7 GHz frequency (a) all switches ON (b) all switches OFF

(a) (b)

91

Table 5.2 Simulated results for Swastika-shaped frequency reconfigurable antenna

5.3 Fabrication of Antennas

FR4 epoxy of 1.6mm thickness, relative permittivity (εr) of 4.4 and dielectric

loss tangent (tanδ) of 0.02 has been used as substrate material for the fabrication of

the antennas. Though the loss tangent of FR4 is high resulting in low gain but easy

availability and cost are also considerable factors. The patch dimensions are shown in

Table 5.1. Two prototypes (with and without conductors representing the ideal ON

and OFF condition of switches respectively) are fabricated using standard silk screen

printing method of PCB fabrication. Double sided copper layer substrate was used.

On one side, the patch was printed and the other side has been used as ground plane.

After preparation of the prototype, SMA connector was soldered to the bottom side of

the substrate for probe feeding. These fabricated antennas are shown in Figure 5.23

and Figure 5.24.

Figure 5.25 shows the fabricated antenna with four PIN diodes BAR63-03W

as switches. The data sheet of this diode may be obtained from [98]. When the diodes

are forward biased, they act as short circuit and when the diodes are reverse biased or

unbiased, they act as open circuit. A simple biasing arrangement of the PIN diodes is

shown in Figure 5.26. The cathode of each diode has been connected to the ground

through 1KΩ resistor. The anode of each diode is connected to the center circle which

is further connected to one resistor of 1KΩ. To make diodes ON, a +5V supply has

been given to anodes through 1KΩ resistor and circular patch while ground has been

connected to all four cathodes through 1KΩ resistors. The diodes are OFF as soon as

the +5V supply is removed.

Parameter All Switches ON

fr = 5.81GHz

All Switches OFF

fr = 5.23GHz

Peak Directivity 4.2767 3.59

Peak Gain 1.5979 2.4

Radiation Efficiency 0.37 0.67

92

Fig. 5.23 Photograph of fabricated antenna showing conductor for all switches ON condition

(a) Top side showing patch (b) Bottom side showing ground plane and SMA connector

(a) (b)

Fig. 5.24 Photograph of fabricated antenna showing gaps for all switches OFF condition (a) Top side showing patch (b) Bottom side showing ground plane and SMA connector

(a) (b)

93

5.4 Comparison of Simulated and Measured Results

The measurements for return loss and E and H plane radiation patterns for

Gain Total of the fabricated antennas were carried out with the same measurement

setup described in chapter 4. The measured and simulated return loss plots (S11

Fig. 5.25 Photograph of fabricated antenna with PIN diode BAR63. The top side is showing

patch, four diodes and bias circuit

Fig. 5.26 A simple biasing arrangement for BAR63 PIN diodes on the patch. The value of

resistors is 1KΩ.

94

parameter) for full Swastika patch (all switches ON condition represented by the

presence of conductor) are shown in Figure 5.27. The shapes of the curves are similar

but shifting of the curve at some dips are seen. The comparison of simulated and

measured results of return loss has been presented in Table 5.3. The measured and

simulated return loss plots (S11 parameter) for full Swastika patch with gaps (all

switches OFF condition represented by the absence of conductor) are shown in Figure

5.28. The measured curve is just following the simulated curve with very small shift.

The comparison of simulated and measured results of return loss in all switches OFF

condition has been presented in Table 5.4. Similar to the results obtained for the

prototype representing all switches ON condition, here also, the measured bandwidth

is more than the simulated bandwidth.

Table 5.3 Simulated and measured results of return loss plots for all switches ON

Parameter All Switches ON

Simulated Measured

Resonant Frequency (fr) 5.81GHz 5.81GHz

Return Loss at fr -25.7dB -17.86dB

Lower -10dB Frequency 5.742GHz 5.725GHz

Upper -10dB Frequency 5.868GHz 5.875GHz

Bandwidth 126MHz 150MHz

Fig. 5.27 Return loss plots for all switches ON condition

Ret

urn

Lo

ss (

dB

)

Frequency (GHz) 1 2 3 4 5 6 7 8 9 10

-30

-25

-20

-15

-10

-5

0

Curve Info Simulated Measured

95

Table 5.4 Simulated and measured results of return loss plots for all switches OFF

Parameter All Switches OFF

Simulated Measured

Resonant Frequency (fr) 5.23GHz 5.275GHz

Return Loss at fr -30.7dB -22.9dB

Lower -10dB Frequency 5.128GHz 5.14GHz

Upper -10dB Frequency 5.323GHz 5.38GHz

Bandwidth 195MHz 240MHz

The simulated and measured E and H plane radiation patterns for both the

prototypes are compared in Figures 5.29 to 5.32. It may be noted that all the measured

patterns are in good agreement with simulated patterns except some negligible errors

at few points. The measured magnitude and direction of maximum gain is almost

equal to the simulated results. For all switches ON condition, the measured maximum

Gain Total at Theta equals to -5 degree for E plane is 1.0dB in comparison to

simulated gain of 0.96dB and for H plane, the measured gain is 1.7dB in comparison

to the simulated value of 2.0dB at Theta equals to 90 degree. For all switches OFF

condition, the measured maximum Gain Total for E plane at Theta equals to -5 degree

is 3.8dB in comparison to 3.8dB gain at Theta equals to -4 degree and for H plane, the

Frequency (GHz)

Ret

urn

Lo

ss (

dB

)

1 2 3 4 5 6 7 8 9 10 -35

-30

-25

-20

-15

-10

-5

0

5

Curve Info Simulated Measured

Fig. 5.28 Return loss plots for all switches OFF condition

96

measured gain is 3.8dB at Theta equals to 0 degree in comparison to 3.8dB simulated

value at Theta equals to -2 degree. The results of gain in H plane for all switches ON

condition are having more deviation from simulated results than the other results.

180

0

45

90

135 -135

-90

-45

-8

-6

-4

-2

0

Curve Info Measured Simulated

Fig. 5.29 Simulated and measured E plane radiation patterns at 5.8 GHz for all switches ON condition

0

45

90

135

180

-135

-90

-45

-1.5 -1

-0.5 0

0.5 1

1.5 2


Fig. 5.30 Simulated and measured H plane radiation patterns at 5.8 GHz for all switches ON condition

97

0

45

90

135

180

-135

-90

-45

-2

0

2


Fig. 5.31 Simulated and measured E plane radiation patterns at 5.25 GHz for all switches OFF condition

180

0

45

90

135 -135

-90

-45

-2

0

2


Fig. 5.32 Simulated and measured H plane radiation patterns at 5.25 GHz for all switches OFF condition

98

The antenna fabricated using PIN diodes BAR63 shown in Figure 5.25 was

tested for return loss parameter using HP’s spectrum analyzer model number 8559A

having operating frequency from 0.01 to 21GHz [99-100]. The measurement set up

and results can be seen in Figure 5.33 and 5.34. When the diodes are not biased, a

return loss of about -13dB has been obtained at 5.37GHz which is very less in

comparison to the simulated value. When the diodes are forward biased by giving 5V

DC supply, the diodes are ON and a return loss of about -22dB has been observed at

6.0GHz resonant frequency. It has been observed that the resonant frequency has been

shifted in both the cases when the diodes are connected.

Fig. 5.34 Return loss measurement when diodes are ON

Fig. 5.33 Return loss measurement when diodes are OFF

99

5.5 Summary

A single layer, compact size Swastika-shaped frequency reconfigurable

microstrip patch antenna for WLAN indoor and outdoor applications has been

studied, designed and fabricated in this chapter. In the study part, all the parameters of

the design have been varied one by one around the optimized value while keeping all

the other parameters at their optimized value. The normal form of Swastika without

four dots was simulated and all its relevant parameters were detected which revealed

that the electric field distribution was asymmetric in nature. After adding four dots,

one in each quarter, the distribution of electric field became symmetric. The addition

of four dots and inclined sections at the end of L-shaped section represents the most

standard form of Swastika being used at different occasions.

The antenna has been designed to operate at 5.2GHz when all the switches are

OFF and at 5.8GHz when all the switches are ON. The switches are assumed to be

ideal and two prototypes are developed. The dimension of the antenna is 50×50mm2.

The measurements of return loss (S11 parameter) and the E and H plane radiation

patterns are carried out using industry standard measurement set up. The proposed

antennas have simulated return loss of -30.7dB at 5.23GHz and -25.7dB at 5.81GHz.

The simulated bandwidth in all switches ON and all switches OFF conditions are

126MHz and 195MHz respectively. The fabricated prototype antennas have measured

return loss of -22.9dB at 5.275GHz and -17.86dB at 5.81GHz. The measured

bandwidth in all switches ON and all switches OFF conditions are 150MHz and

240MHz respectively. A good agreement between simulated and measured return

loss, E plane and H plane radiation patterns have been observed for the two

prototypes. The simulated peak gains of 2.43dB and 1.6dB are observed at 5.2GHz

and 5.8GHz resonant frequency respectively. The low gain is the result of substrate

properties.

As an experiment, the BAR63-03W PIN diodes are placed on the antenna for

the switching purposes. When the diodes are ON, a return loss of -22dB has been

observed at 6.0GHz resonant frequency and when the diodes are unbiased, the

resonant frequency is 5.37GHz with return loss of -13dB. Though the data sheet

recommends the diodes to be used up to 3GHz only because of increased insertion

100

loss but it was an effort to understand the effect of using practical switches in the

microstrip patch antennas. The variations in the results may be due to the

characteristics of diodes and the biasing wires present on the antenna structure. The

use of switches which do not need bias lines and circuit is very important for

reconfigurable antennas because the presence of additional lines or wires on the

radiator degrades the radiation performance of any antenna since the RF leakage

through the bias lines cannot be avoided.

The measured results verify the good performance of proposed antenna but

due to the substrate properties, low gain performance of the proposed antenna has

been observed.

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