Reflection Properties of three different Substrates on Circular Microstrip Patch Antenna

(1)

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 9, September 2012)

177

Reflection Properties of three different Substrates on Circular

Microstrip Patch Antenna

Anzar Khan

1

, Puran Gour

2

, Rajesh Nema

3 1,2,3 _{NIIST, Bhopal (M.P.), India}

Abstract —Communication Systems are being investigated for S, C, X and Ku bands. For portable systems, the size and cost of the antenna are of great importance. Microstrip antennas show promise due to their small and conformal features, and their ability to be mass manufactured. The bandwidth and return losses are also of great importance. A project is currently underway to examine the characteristics of three dielectric substrates believed suitable for microstrip antenna applications in the X-band. These substrates are Bakelite, ℰr of 4.78 and tan δ of 0.03045, RT Duroid, ℰr of 2.2 and tan δ of 0.0004 and Polyester, ℰr of 1.39 and tan δ of 0.01 specified at 10 GHz frequency. A microstrip antenna is designed with triangular patch of fixed resonant frequency of 10 GHz and fixed height of 1.5 mm.

Keywords —Microstrip patch antenna; organic substrates; polyester; X-bands; return loss

I. INTRODUCTION

Now a days, communication devices need high frequency compact antennas. Microstrip patch antennas are popular choices because of their low profile and conformal structures. The patches can be of different geometry like rectangular, triangular, circular, elliptical or any other shape. In spite of numerous advantages of microstrip patch antennas it is difficult to achieve a better tradeoff between the gain, bandwidth and more prominently the size of antenna. In practice, different dielectric substrates are used for manufacturing microstrip patch antennas. It is believed that dielectric substrates with dielectric dielectric constants in the range 2.2 ≤ ℰr ≤ 12r gives better results. Now a days synthetic or natural materials are also used as substrates to manufacture these antennas. The work presented in this paper is the comparison of synthetic substrate, polyester with the natural dielectric substrates Bakelite and RT Duroid for manufacturing triangular microstrip patch antenna using IE3D Simulator. IE3D has unlimited unknown, magnetic current modeling, iterative matrix solver and Genetic EM optimizer. It also includes the pattern view for full radiation pattern handling capabilities.

II. ANTENNA DESIGN

Microstrip patch antenna is designed with circular patch. The radius of the patch is calculated by the formula as given below- 1 2

2

1 1.7726

2

r n

F

a

h









_







_









_



_



_



_







Where

a

is radius in mm,

c

is the velocity of light 11

3 10

mm s

/

 

,

E

r

is the dielectric constant of the dielectric substrate. The resonant frequency is taken as 10 GHz and the height of the substrate is 1.5 mm.

F

is given as- 9

8.791 10

r r

F

f







The effective radius is given by-

1 2

2

1 1.7726

2

e n r

a

h

a

h



















_



_

_

_



_

_













Coaxial Feed

The Coaxial feed or probe feed is a very common technique used for feeding Micro strip patch antennas. The inner conductor of the coaxial connector extends through the dielectric and is soldered to the radiating patch, while the outer conductor is connected to the ground plane. The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the patch in order to match with its input impedance. This feed method is easy to fabricate and has low spurious radiation.

A. Bakelite

(2)

International Journal of Emerging Technology and Advanced Engineering

178

9 9

9

8.791 10

10 10

4.78

0.402

4.02

r r

F

f

cm

mm



















1

2

4.02 1 0.04969 3.209

4.02

3.736 1.1594

a







Effective radius is given by-

1 2

2

1 1.7726

2

e n r

a

h

a

h



















_



_

_

_



_

_

















12

3 3.736 1

3.912 1.7726

56.1028

4.066

e n

a

mm







_



_







Probe feed to patch is given on

x

= -4.066 and

y

= 0

It can be seen that probe feed to patch is on the edge of the structure, it is because it gives good results on this position compared to other position.

B. RT Duroid

Dielectric constant of RT Duroid is



_r= 2.2 and loss tangent, tan δ is 0.0004. Thus, the effective radius is given as-





12

3 5.2722 1

5.5210 1.7726

36.4388

5.98

e n

a

mm







_



_







where, 9 9 9

8.791 10

10 10

2.2 0.5926

5.926

r r

F

f

cm

mm











5.2722

a



mm

x

= 0 and

y

= -6

Again in this structure the feed point is given on the edge of the patch because of good results.

C. Polyester Substrate

(3)

International Journal of Emerging Technology and Advanced Engineering

179





12

3 6.4058 1

6.708 1.7726

27.972

8.93

e n

a

mm







_



_







Where,

9 9

9

8.791 10

10 10

1.39

0.745

7.45

r r

F

f

cm

mm











6.4058

a



mm

x

= 0 and

y

= -5

Here, the feed point is at different position. Instead of on the edge of the geometry, it is inside the structure. The results are found to be best in this position. It is also worth noticing that as the value of dielectric constant decreases, the size of the antenna increases.

III. SIMULATION RESULTS

A. Return loss vs. frequency graphs Bakelite

Bakelite with dielectric constant, ℰr = 4.78 when simulated on 10 GHz frequency gives a good return loss of -14.40 dB on 10 GHz frequency.

RT Duroid

(4)

International Journal of Emerging Technology and Advanced Engineering

180

Polyester Substrate

Clearly, Polyester has better return loss than the other two substrates but there is difference between simulated frequency (10GHz), and output frequency (8GHz). This is due to the fact that Polyester substrate has very low dielectric constant than the other two natural substrates.

B. G a i n vs. Frequency Graph Bakelite

Gain vs. frequency graph given above clearly indicates that for the given circular geometry the gain of the antenna is 2dBi approximately. This gain is very low. One of the reasons for this low gain is its high dielectric constant.

RT Duroid

The graph above shows that the gain of the microstrip patch antenna is about 5.5dBi (approx.). This gain is much better than the gain of the microstrip patch antenna using Bakelite for the same frequency and height. The difference between the gain of the two antennas is about 3.5 dBi which is not surprising because of the huge difference between their dielectric constants.

(5)

International Journal of Emerging Technology and Advanced Engineering

181

C. E f f i c i e n c y v s . F r e q u e n c y G r a p h Bakelite

RT Duroid

IV. RESULTS AND DISCUSSION

Substrate Bakelite RT Duroid Polyester

Dielectric constant

4.78 2.2 1.39

Loss tangent 0.03045 0.0004 0.01

Output frequency

10 GHz 10 GHz 8 GHz

Radius 4.066 mm 5.98 mm 8.93 mm

Return loss -14.40 dB -15.09 dB -15.96 dB

Gain 3.164 dBi 6.545 dBi 7.02 dBi

Directivity 6.5 dBi 7 dBi 8.029 dBi

The table given above shows that Bakelite has the highest dielectric constant among the three substrates. That is why the size of the antenna is minimum compared to other two antennas using low dielectric constants. However, its gain is very low. RT Duroid gives a good return loss and its gain is also high close to 5.5 dBi which is very good although its antenna size is bigger than the first antenna. Of the three antenna, Polyester gives better gain and return loss. Obviously, the size of the antenna is bigger than the other two. We have to do compromise between the size of the antenna and the gain and return loss of the antenna as the situation demands.

V. CONCLUSION

All the three dielectric substrates Bakelite, RT Duroid and Polyester used for the manufacturing of microstrip patch antennas are investigated. Results are found to be best in the case of Polyester substrate, although the size of the antenna increases due to its low dielectric constant. Polyester substrate can be used to manufacture textile or cloth based wearable antenna and should communicate the voice, data or biotelemetry signals at high data rates. By using Polyester substrate, a gain of 7.8 dBi and return loss

of -15.96 dB can be achieved. ACKNOWLEDGEMENTS

(6)

International Journal of Emerging Technology and Advanced Engineering

182

REFERENCES

[1 ] Microstrip patch antenna with dielectric substrate; D.D.Sandu, O. Avadanei, A. Ioachim, G. Bariu and P. Gasner; Journal of Optoelectronics and Advanced Materials; vol.5, No.5, 2003, p.1381-1387.

[2 ] Jawed Y. Siddique and Debatosh Guha, ‘‘Applications of Triangular Microstrip Patch Antenna : Circuit Elements to modern wireless antennas.’’

[3 ] Rajesh K Vishwakarma, J A Ansari and M K Meshram, ‘‘Equilateral triangular microstrip antenna for circular polarization dual –band operation’’, Indian Journal of Radio & Space Physics, vol. 35, August 2006, pp. 293-296.

[4 ] Input impedance and resonance characteristics of superstate-loaded triangular microstrip patch. M. Biswas and D.Guha.

[5 ] Dinesh Yadav, ‘‘L-Slotted rectangular microstrip patch antenna’’, 2011 International conference on communication systems and network technologies.

[6 ] Vedaprabhu. B and K.J. Vinoy, ‘‘ A double U-Slot patch antenna with dual wideband characteristics’’, IEEE, 2010.

[7 ] K. Naga Mallik, Ch. Radhika, D Ujwala, H.M. Ramesh, A. Gowtham Kumar, P.Karthik,‘‘ A compact microstrip patch antenna with triangular snipped slot for wireless applications.’’,International Journal of Engineering and Advanced Technology ( IJEAT ), ISSN:2249-8958, volume-1, issue-4, April2012.

[8 ] Ashvini Chaturvedi, Yogesh Bhomia and Dinesh Yadav, ‘‘ Truncated tip triangular microstrip patch antenna’’, IEEE 2010. [9 ] Metamaterial embedded wearable rectangular microstrip patch