Multi-band Antenna Designs for Satellite Applications

Milind S.Shah, Prof. Sanjeev Gupta Dhirubhai Ambani Institute of Information and Communication Technology

Gandhinagar, Gujarat, India shahmilinds@gmail.com, sanjeev_gupta@daiict.ac.in

Abstract— In this paper design of single multiband fractal antenna for satellite applications is presented. These proposed antennas are compact in size and can operate in L, S, C and X band. Here three different designs are suggested based on different feeding techniques and different geometry. All designs are based on the fractal geometries. Fractals have no characteristic size, and are generally composed of many copies of themselves at different scales. These unique properties of fractals have been exploited in order to develop a new class of antenna-element design that are multi-band and/or compact in size.

Keywords- fractal antenna, multiband antenna, sirpenski geometry, multifractal technique, cantor fractal.

I. INTRODUCTION Fractal geometries have recently been introduced in the

design of antennas and attracted wide interest due to its various important characteristics. Space-filling ability of fractal, help to miniaturize size while keeping large electrical length. This property helps to build small size antennas for mobile communication and other such applications. Also, they can easily fit into package. More effective coupling from feeding transmission line to free space can be achieved in less volume. Due to self similarity properties associated with fractal geometry structures, fractal antenna can be designed with multi-band performance[1]. Improved impedance and SWR performance on reduced physical area can also be obtained. Polarization and phasing of fractal element antenna is also possible with reduced construction cost[2].

In this paper proposed structures are able to operate on L,S,C and X band. Major target application area for these antennas is satellite navigation and remote sensing. This design is compact compared to separate antenna for each band. Single antenna also reduces the problem of generation of undesired radiation mode[3].

The rest of the paper is organized as follows. In section-II electromagnetically coupled fractal antenna design resonating at three frequencies is discussed and simulated results are also shown. While in section-III design of aperture coupled fractal antenna and simulated result are shown. In section IV cantor based fractal antenna is discuss. All the results are simulated with ADS[4] momentum. Section-V concludes the paper.

II. ELECTRO-MAGNETICALLY COUPLED FRACTAL ANTENNA

The general structure of electro-magnetically coupled antenna is shown in Fig. 1[5]. Feed line is placed between

patch and ground plane, separated by two dielectric media. The technique eliminates spurious feed network radiation. Also by proper selection of two dielectric media, performance can be optimized. Two layers should be aligned properly. Here the radiating patch is consist of sirpenski carpet geometry shown in Fig. 2, while feeding patch is simple rectangular patch as shown in Fig. 3 (all dimension are in mm)[6]. The dimension of radiating patch is same as of Fig. 8. In Fig. 2 the shadowing region is showing the metal layer. So the radiating patch is collection of rectangular patches arranged in the form of sirpenski carpet.

The simulated result for this antenna is shown in Fig. 4. The dielectric material used in this design is having dielectric constant єr1=єr2 = 2.2. The thickness of the both layer is 1.6mm. Table-I is showing the antenna parameter at various resonating frequencies.

The radiation patterns at various different resonating

frequencies are given in Fig. 5. The radiation pattern is becoming more and more directional for high operating frequency.

Feeding patch

Radiating patch

Co-axial feeding line Ground Plane

Figure 1. Electro-magnetic coupling

66

66

. Feeding point

Figure 2. Feeding patch

Feeding point

Figure 3. Radiating patch of shape 2-iteration sirpinski carpet with feeding point

III. APERTURE COUPLED FRACTAL ANTENNA The general structure of aperture coupled patch antenna is

shown in Fig. 6[3]. Here field is coupled from microstrip line feed to radiating patch through small aperture. Fig. 7 is showing the geometry of aperture coupled fractal antenna working at L, S, C and X-band. Here radiating patch is fractal antenna with 2 iterations of sirpenski carpet, while lower patch is feedline coupled to the upper patch through an aperture. The dimension (in mm) of sirpenski carpet fractal is shown in Fig. 8.

Due to enhanced performance aperture coupling[7] is becoming increasing popular as a means of producing patch arrays. Because the feed lines are behind the ground plane, no spurious radiation escapes to corrupt the side lobes or polarization of the antenna. The coupling aperture is usually centred under the patch and low levels of cross-polarization can be achieved.

Figure 4 Simulated return loss of EM coupled Fractal antenna

Major disadvantage of this type of coupling is multilayer fabrication required. Aperture coupling to a patch antenna from the stripline is not as strong as for a microstripline feed. Care must be taken to suppress the parallel plate mode that can be excited in the stripline[8].

The simulated return loss of aperture coupled fractal antenna is shown in Fig. 9. The patch is printed on a microwave substrate of the thickness h = 1.6mm and the relative permittivity єr = 2.2. The simulate antenna parameters at various resonating frequencies are given in Table-II. The radiation patterns at various frequencies are also given in Fig. 10. Here also the directivity is increasing as we increase frequency.

TABLE-I Performance Parameters of EM Coupled Fractal Antenna At Different Resonating Frequencies

Marker No. Frequency(GHz) S11(dB) Zo(Ω) Gain(dB) Directivity(dB) BW(MHz)

m1 1.4506 -20.684 52.25 6.193 7.47 14 m2 2.914 -11.378 74.9 4.63 6.3 400 m3 7.338 -34.259 48.9 6.79 10.66 25 m4 9.375 -37.79 51 6.12 9.75 70

(a) (b) (c) (d)

Fig. 5. Simulated radiation patterns of EM coupled fractal antenna at (a) 1.450GHz (b)2.914GHz (c)7.388GHz (d)9.375

Figure 6 Aperture coupling

4. 8 10

Aperture Feed line

Figure 7 Aperture coupled Fractal antenna

Mag

. [dB

]

Figure 9 Simulated return loss of Aperture coupled

Fractal antenna

(d)

(b)

(e)

Fig. 10. Simulated radiation patterns of aperture coupled fractal antenna at (a)1.406GHz (b)7.063GHz (c)8.656GHz (d)10.25GHz (e)11.44GHz

IV. CANTOR BASED SINGLE LAYER FRACTAL ANTENNA To alleviate the problem of multilayer structure other

fractal geometries have been tried to obtain desired result. Cantor geometry is selected here due to its simple construction and prominent results. As microstrip antennas are giving narrow bandwidth, monopole structure is utilized to achieve higher bandwidth. Here microstrip feed line is designed to feed the radiating element. Location of feedline is optimized to achieve good return loss behaviour. The structure of the cantor based antenna is shown in Fig. 11[9] with all dimensions are in mm.

The simulated return loss of cantor fractal antenna is shown in Fig. 12. The patch is printed on a microwave substrate of the thickness h = 1.6mm and the relative permittivity єr = 2.2. The simulate antenna parameters at various resonating frequencies are given in Table-III. The radiation patterns at various frequencies are also given in Fig. 13.

22 14.4

7. 3 6. 6

Figure 8 Fractal radiating patch of shape 2-iteration sirpinski carpet

Figure 11 Cantor based Fractal antenna Figure 12 Simulated return loss of Cantor based Fractal antenna

(a) (b) (c) Fig. 13. Simulated radiation patterns of cantor based fractal antenna at (a) 1.4GHz (b) 5.35GHz (c) 9.65GHz

V. CONCLUSION In this paper we have proposed fractal based antenna with

different fractal geometries and different feeding techniques for L, S, C and X band applications. By the use of fractal we get the advantage of miniaturization and by the aperture coupling and EM coupling we get ease in impedance matching for feeding network and by utilization of other fractal geometries single-layer structure can be achieved. In addition the antenna provides flexibility in frequency of operation and bandwidth. We can achieve desired frequency of operation by optimizing the various dimension of the design.

TABLE-II Performance Parameters of Aperture Coupled Fractal Antenna At Different Resonating Frequencies

Marker No. Frequency(GHz) S11(dB) Zo(Ω) Gain(dB) Directivity(dB) BW(MHz)

m1 1.406 -19.187 40.9 4.78 7.6 36 m2 7.063 -22.798 52.5 2.02 8 1500 m3 8.656 -33.590 50.4 2.83 9.23 77 m4 10.25 -33.663 51 8.11 11.25 290 m5 11.44 -25.223 48.25 10.12 10.66 260

TABLE-III Performance Parameters of Cantor Based Fractal Antenna At Different Resonating Frequencies

Marker No. Frequency(GHz) S11(dB) Zo(Ω) Gain(dB) Directivity(dB) BW(MHz)

m1 1.4 -28dB 48.7 4.8 5.1 50 m2 5.35 -24dB 48.3 5.7 6.4 458 m3 9.65 -27dB 48.5 7.2 7.7 575

2 4 6 80 10

-30

-20

-10

0

-40

10

Frequency

Mag

. [dB

]

m1m2 m3

S11

REFERENCES

[1] J. J. Huang, F. Q. Shan, and J. Z. She, “A Novel Multiband and Broadban Fractal Patch Antenna”, Progress In Electromagnetics Research Symposium, Cambridge, USA, March 26-29, 2006, pp. 57-59.

[2] Kiyun Han, and Frances J. Harackiewicz, “Stacked multiband fractal patch antennas” Antenna and propagation society international symposium, June 2003.

[3] Ramesh Garg,Prakash Bhartia, Inder Bahl and Apisek Ittipiboon, “Microstrip Antenna Design Handbook”, Artech House.

[4] Agilent Technologies, “Advance Design System ADS 2003A”.

[5] Girish kumar, and K.P. Ray, “Broadband Microstrip Antennas”, Artech House.

[6] M.K.A Rahim,N. Abdullah, and M.Z.A. Abdul Aziz, “Microstrip Sierpinski Carpet Antenna Design”, Proceedings of Asia-Pacific Conference on Applied Electromagnetics, December 20-21, 2005.

[7] D.M.Pozar, “Microstrip antenna aperture coupled to a microstripline,” Electronics Letters, vol.21, pp 49-50, Jan 1985.

[8] Daniel H. Schaubert, “A review of some microstrip antenna characteristics”, Microstrip antennas, IEEE Press, 1995

[9] B. Manimegalai, S. Raju and V. Abhaikumar, “A Multifractal Cantor Antenna for Multiband Wireless Applications” , IEEE Antennas Wireless Propag. Lett., vol. 8, pp. 359–362, 2009