A Novel Hexagonal Boundary Fractal Antenna with Band Notch Characteristics

A Novel Hexagonal Boundary Fractal Antenna with Band Notch Characteristics

Sreerag M Student

1. Tech in communication engineering Nss college of engineering Palakkad, kerala-678008

   Sudha T Professor

   Department of electronics and communication Nss college of engineering Palakkad, kerala-678008

   AbstractA novel coplanar waveguide (CPW) fed hexagonal shaped antenna for Ultra Wide Band (UWB) applications with WLAN band-notch characteristics is proposed in this work. The proposed antenna covers the entire UWB bandwidth of 3.1 to 10.6 GHz with band rejection in the range 5.1 to 5.9 GHz. The rejection in WLAN range reduces interference between ultrawide band and WLAN band. Band rejection is achieved by etching rectangular slot on the radiating element.

   KeywordsUltra Wide Band, Band notch, WLAN, CPW, Fractal Antenna

   1. INTRODUCTION

      Ultra Wide Band (UWB) systems can be characterised by a system with relatively large bandwidth. As per FCC standardisation, UWB is allocated a frequency range of 3.1 to 10.6 GHz for its operation with a power emission level of -41.3 dBm/MHz. IEEE 802.15.3 standardisation group was formed to establish a standard for high speed communication based on UWB. UWB band is divided into lower (3.1 to 5.15 GHz) band and upper (5.875-10.6 GHz) bands. Due to baseband nature of signal transmission, UWB system have potentially low complexity and low cost. Other advantages includes high data rate, low power consumption, resistant to multipath and jamming. Several applications of UWB antennas are EM measurement, wireless communications, radars, medical imaging, localisation and wireless sensor networks. Particular UWB antenna is selected based on the requirements [1] – [3].

      UWB can coexist with other communication systems. Traditional narrow bands like WLAN, X bands overlap with UWB. In order to avoid interference, band stop performance is needed. There are different techniques like tuning stub, insertion of shaped slots, using parasitic element, implementing fractal geometry to notch any unwanted frequencies [4]. Band rejection in the range 4.7 to 5.9 GHz can be obtained by embedding spur lines on the ground plane [5]. UWB antenna with hilbert curve slots on radiating element is used for WLAN/WiMAX applications is proposed in [6]. CPW fed UWB antenna with dual notch band is reported in [7]. Here split ring slot in radiator and slots in ground plane are used to achieve rejection. A partial annular

      slot is embedded at lower portion of annular ring shaped radiating patch to cover entire UWB band with rejection at WLAN band is considered [8]. Circular boundary Sierpinski carpet fractal with band notch is achieved by etching meandered slot from radiator. Band rejection obtained is 5.15

      – 5.825 GHz [9]. Fractal antennas are based on the concept of a fractal, which is a recursively generated geometry that has fractional dimensions. A fractal antenna is capable of operating at many different frequencies simultaneously.

      In this work hexagonal boundary fractal antenna for WLAN applications is proposed. Band rejection in the WLAN range of 5.1 to 5.9 GHz is achieved by etching slots on the radiating element. The proposed system covers entire UWB bandwidth and desired radiation patterns are obtained.

      This paper is organized as follows. Section II describes antenna design and section III gives parametric study. In section IV simulation results are discussed. Finally section V draws the conclusion. Antenna is designed and investigated using high frequency structure software (HFSS).

   2. ANTENNA DESIGN

      The geometrical configuration of proposed antenna is shown in Fig.1. An FR4 substrate with relative permittivity of 4.4, a loss tangent of 0.02 and a thickness of h=1.59 mm is used for the proposed antenna. The substrate is having a cross section of 40×38 mm. The proposed antenna uses a CPW fed hexagonal boundary sierpinski carpet fractal structure. The 50 ohm CPW fed structure consists of the CPW transmission signal strip line with a signal strip width 2.6 mm. A partial ground plane is used for this structure. The length of the ground plane Lg and the width of the ground plane Wg are important design parameters, where Lg= 18.14 mm and Wg=17 mm.

      Initiator for this hexagonal boundary carpet fractal is a hexagonal shaped antenna. First iteration of this fractal antenna is obtained by etching out central hexagon of 6mm size,which is one third size of the initiator. Next iteration is obtained by subtracting additional four hexagons of one third size of center hexagon. Band rejection in WLAN frequency

      range is obtained by etching a slot combined by circles and rectangles.

      Fig. 1. Antenna structure

      Fig. 2. Slot for band rejection

   3. PARAMETRIC STUDY

      Parameter study of the slot etched on the patch is performed. The antenna has a rectangular slot of width Ws. Length of this slot is denoted by Ls which is a combination of L1,L2,L3 and L4. From the four corners of this slot, four circles are also etched. This combinational slot is responsible for the band rejection in the region 5.1- 5.9 GHz. When total length of slot Ls is 29.4 mm, band rejection is obtained in the range

      4.5 GHz to 4.9 GHz. As length of slot Ls is increased from

      29.4 mm to 31.8 mm, band notched region shift towards

      higher frequency side. Variation of frequencies with changing length is shown in Table.I. Matching over the band also increases with increase in length. An optimum slot length of

      31.4 mm is selected for achieving the desired band rejection.

      Length of slot ( Ls)	Band Rejection
      29.4 mm	4.5 GHz – 4.9 GHz
      29.8 mm	4.8 GHz – 5.5 GHz
      30.8 mm	4.9 GHz – 5.7 GHz
      31.4 mm	5.1 GHz – 5.9 GHz
      31.8 mm	5.2 GHz – 6 GHz

      TABLE. I PARAMETERIC STUDY ON LENGTH

      Width of slot is also a significant design parameter. When width of slot is selected as 0.2 mm, desired band rejection in the range 5.1 GHz to 5.9 GHz is obtained. Slot width is adjusted while fixing the length of rectangular slot as 31.4 mm and radius of circle as 0.4 mm. As slot width Ws is increased from 0.2 mm to 0.4 mm, notch band shift towards lower frequency side. An optimum slot width of 0.2 mm gives the desired band rejection. Table.II gives the variation of notch band when width of the slot is changed.

      Length of slot (Ls)	Width of slot (Ws)	Band Rejection
      31.4 mm	0.2 mm	5.1 GHz – 5.9 GHz
      31.4 mm	0.3 mm	4.8 GHz – 5.5 GHz
      31.4 mm	0.4 mm	4.3 GHz – 4.7 GHz

      TABLE II PARAMETERIC STUDY ON WIDTH

      Radius r of circular slot also determines notch region. When radius of circle is selected as 0.6 mm, band notch is obtained in the region 4.4 to 4.9 GHz. As the radius is decreased from

      0.6 mm to 0.3 mm, band rejection region is shifting towards higher frequency. Table.III shows the parametric study on radius of circular slot. An optimum radius of 0.4 mm is selected for the required notch characteristics.

      The optimised parameters are Ls =31.4 mm, Ws= 0.2 mm and r = 0.4 mm.

      Width of slot (Ws)	Radius of circular slot (r)	Band Reection
      0.2 mm	0.6 mm	4.4 GHz – 4.9 GHz
      0.2 mm	0.5 mm	4.9 GHz – 5.7 GHz
      0.2 mm	0.4 mm	5.1 GHz – 5.9 GHz
      0.2 mm	0.3 mm	5.2 GHz – 6.1 GHz

      TABLE III

      PARAMETERIC STUDY ON RADIUS OF CIRCULAR SLOT

   4. RESULTS AND DISCUSSION

      Antenna is investigated using high frequency structure software (HFSS) version 15 based on finite element method (FEM). The simulated results are discussed below.

      1. Return Loss

         Simulated return loss curve of proposed antenna is given in Fig. 3. Simulated result shows that, the proposed antenna provides a sharp band notch of 5.1 to 5.9 GHz. Impedance bandwidth range from 3 GHz to 11 GHz and the bandwidth covers entire UWB band. Return loss upto -33.18 dB is obtained at 10.4 GHz which shows better impedance matching. Better return loss values are obtained at other resonant frequencies also. Hence the proposed system can perform in the entire UWB band and avoids the interference from the WLAN systems operating in 5.1-5.9GHz.

         Fig. 3. Return Loss of proposed antenna

      2. Radiation Pattern

         Radiation patterns at E plane and H plane are analysed at 3 different frequencies. Nearly omnidirectional radiation patterns are obtained for H plane at frequencies 6.2 GHz, 8.6 GHz and 10.5 GHz.

         Fig. 4. Radiation Pattern at 6.2 GHz

         Fig. 5. Radiation Pattern at 8.6 GHz

         It is noticed from the radiation patterns of proposed fractal antenna, dipole like radiation characteristics are obtained for the E Plane. There is slight distortions in the E plane characteristics due to band rejection function.

   5. CONCLUSION

A novel CPW fed Hexagonal boundary carpet fractal antenna with band notch characteristics has been proposed in this paper. Antenna has simple and easy to fabricate structure. The designed antenna covers entire UWB bandwidth of 3.1 to 10.6 GHz. By etching a rectangular shaped slot, interference to 5.1 to 5.9 GHz band assigned for IEEE 802.11a and HIPERLAN/2 is reduced. Gain upto 4.1 dB is achieved and omnidirectional radiation patterns are obtained over the required bandwidth.

REFERENCES

1. Gain

Fig. 6. Radiation Pattern at 10.5 GHz

Simulated gain of the proposed hexagonal boundary

1. Arne Svensson, Arumugam Nallanathan, Ahmed Tewfik, Ultra- Wideband Communication Systems: Technology and Applications, EURASIP Journal on Wireless Communications and Networking, Article ID 16497, Pages 13,2006.

2. Ultra Wide Band Antennas Design and Application, Daniel Valderas, Juan Ignacio Sancho, David Puente, Cong Ling, Imperial College press, London ,pg no:167-168.

3. UWB Theory and Applications, Ian Oppermann, Matti Hama la inen and Jari Iinatti, John Wiley and sons Ltd.

4. Mohammad Jahanbakht, Abbas Ali Lotfi Neyestanak, A Survey on Recent Approaches in the Design of Band Notching UWB Antennas, Journal of Electromagnetic Analysis and Applications, pp. 77- 84,2012.

5. H. J. Lee, Y. H. Jang, and J. H. Choi, Design of an UWB Antenna with Band-rejection Characteristic, Progress In Electromagnetics Research Symposium , Prague, Czech Republic, pp.155-157, August 27-30,2007.

6. D. O. Kim and C. Y. Kim, Planar UWB Antenna with WLAN/WiMAX Dual Band-notched Characteristics Using the Hilbert-curve Slots, PIERS Proceedings, Kuala Lumpur, MALAYSIA, pp.1494-1497, March 27-30, 2012.

7. Z.-A. Zheng and Q.-X. Chu, Compact CPW-Fed UWB Antenna With Dual Band-Notched Characteristics, Progress In Electromagnetics Research Letters, Vol. 11,pp. 83-91, 2009.

8. R. Azim and M. T. Islam, Compact Planar UWB Antenna With Band Notch Characteristics For WLAN And DSRC, Progress In Electromagnetics Research, Vol. 133, pp. 391-406, 2013.

9. R.Ghatak, A. Karmakar, D. R. Poddar, A Circular Shaped Sierpinski Carpet Fractal UWB Monopole Antenna With Band Rejection Capability, Progress In Electromagnetics Research C, Vol. 24, 221- 234, 2011.

fractal antenna is shown in Fig.7. Simulated result shows that gain is relatively flat over the entire UWB band and maximum gain upto 4.1 dB can be achieved around 8 GHz. There is a significant reduction of gain in the WLAN band as expected.

The proposed antenna can perform well in the UWB band with a rejection in the 5.1 to 5.9 GHz.

Fig. 7. Gain