On the Design of CPW Fed Appollian Gasket Multiband Antenna

Transcription

1 On the Design of CPW Fed Appollian Gasket Multiband Antenna Raj Kumar and Anupam Tiwari Microwave and MM Wave Antenna Lab., Department of Electronics Engg. DIAT (Deemed University), Girinagar, Pune , India Abstract- This paper presents CPW - fed Appollian fractal antenna. The Antenna has been designed on FR4 substrate ε r = 4.3 and thickness 1.53 mm. The antenna has been fabricated and tested using VNA. The experimental result shows the multiband behavior with the centre frequencies of 1.52 GHz, GHz and 7.44 GHz corresponds to impedance bandwidth of 70%, 27.7% and 32.6 % respectively. The experimental radiation pattern of the antenna has been observed near to omnidirectional at lower frequency and like electric dipole antenna at higher frequency. The cross polarization level of antenna is better than 11.4 db. This antenna can be used for GPS, PCS, Vehicular radar and imaging system applications. Index Terms - Fractal antenna, Multi-bands Resonant Frequency, Sierpinski gasket and Miniaturization. I. INTRODUCTION The progress in wireless and dramatic development of a variety of wireless applications have remarkably increases the demand of multiband/wideband antennas with smaller dimensions than conventionally possible. This has initiated antenna research in various directions, one of which is by using fractal shaped antenna element [1]. There are an important relation between antenna dimensions and wavelength. This relation states if antenna size less than λ/2 then antenna is not efficient radiator because radiation resistance, gain and bandwidth are deteriorated. This is because as size of antenna reduces mismatch between antenna and source increases. Fractal geometry is a very good solution for this problem. In the recent years, self-similarity and space filling geometrical properties of fractal have created interest among researchers in fractal antenna technology to meet the requirement of multi-band /wideband and miniaturization. Sierpinski gasket monopole fractal antenna has been reported by many authors [2-3] for multi-band characteristics based on self-similar property. Whereas, the space filling property leads to curves that are electrically very long but fit into a compact physical space. This property of fractal antenna can lead to miniaturization of antennas [4-6]. In this paper, Appollian gasket Fractal antenna with CPW- fed has been presented for miniaturization, multi-band, good impedance bandwidth and radiation pattern. Such type of antenna is useful for wireless communication. II. ANTENNA GEOMETRY Appollian gasket fractal antenna has been constructed. The solid appollian gasket is made by making the three tangential circles of 90 mm. The intersection of three tangential circle inner part has been taken as appollian gasket. This Solid appollian gasket is called initiator shown in Fig. 1. The dimension from one tip to other tip comes out 42 mm This antenna has been constructed using the space filling property of fractal antenna with circular pattern in spite of triangular in solid apollonian gasket.. In the first iteration, a circle of 12 mm is slotted from solid apollonian gasket configuration. The appollian gasket is then fitted into the circle. This is the first iteration of antenna. In the second iteration, circle of 4 mm, one in centre and three in corner are slotted and appollian are fitted into the all circles. In third iteration, circle of 1 mm radius

2 have been slotted one in centre and three in corners and appollian are fitted into these. The appollian are fitted into the all circles like this that it should touch the metallization properly to make the current continuity. The process can be repeated theoretically infinite time. But because of fabrication constraints, fractal antenna with infinite iteration is not possible. That is why antenna with third iteration has been made keeping in mind the fabrication constraints. Finally, the proposed antenna is shown in Fig. 2. matching. The CPW - Fed has been taken of length 25 mm, width 2 mm and 0.5 mm gap. Dimension of one tip to another of appollian gasket is 42 mm and height of appollian gasket is 32 mm mm. This antenna has been fabricated and tested on vector network analyzer. The photograph of the antenna is shown in Fig. 2. Fig. 2 Apollonian Gasket Fractal antenna with CPW Fed Fig. 1 Initial Solid Appollian gasket Antenna III. DESIGN OF APPOLLIAN GASKET FRACTAL ANTENNA Appollian Gasket Fractal antenna has been designed on FR4 substrate of height h = 1.53 mm and ε r = 4.3. Third iterative Apollonian gasket antenna has been constructed because of fabrication constraints. Appollian gasket fractal antenna shown in Fig. 1 has been fed with alternative feed i.e. coplanar feed. This feeding method leads to better matching for the first resonance frequency in comparison to coaxially fed. The whole structure is uniplanar. CPW-fed line and fractal radiating structure are printed on a single layer dielectric substrate and therefore the whole antenna structure is compact and cheap in production. CPW fed increases the degree of freedom associated with fractal antenna elements to improve the impedance matching characteristics without using any extra matching circuit. In Sierpinski gasket monopole antenna [2], the matching at higher band is better than first band. It is because, in long wavelength range, the current does not reach up to the top of the antenna, resulting in poor matching. The CPW-fed is good for better IV. DISCUSSION AND EXPERIMENTAL RESULTS Appollian based Gasket fractal antenna has been designed on FR4 substrate of height 1.53 mm and ε r = 4.3. Solid Appollian gasket and appollian gasket Fractal antenna with CPW-fed have been fabricated and tested using VNA R& S ZVA40. The simulated and experimental results of solid appollian gasket antenna has been shown in Fig. 3a and 3b. Simulated and experimental results are in good agreement. The experimental result of appollian gasket Fractal antenna i.e return loss versus frequency reveals the multi-band with first, second and third resonance at frequencies 1.52 GHz, GHz and 7.44 GHz respectively as shown in Fig. 4. The first band is shifted relative to second band owing to truncation and can be changed by adequate choice of width of CPW ground plane. First band is much better than [3]. The resonant frequency of solid equilateral triangular monopole patch with coaxial feed is GHz and solid appollian gasket antenna with CPW-fed is GHz respectively as shown in Fig. 3. The lower end frequency of appollian gasket fractal antenna shifted to the lower frequency side to 0.99 GHz

3 in comparison to simple CPW fed appollian gasket resonant frequency GHz and simple coaxial fed equilateral triangular monopole patch GHz. This indicates the size reduction. The impedance bandwidth of the first, second and third band is 1060 MHz, 1290 MHz and 2640 MHz respectively. The impedance bandwidth of each band was measured at minimum return loss 10 db. The Table 1, summarized the impedance bandwidth and fractional bandwidth of antenna for all bands. The experimental radiation pattern of this antenna is nearly omni-directional at lower (in first band) and like electric dipole at higher frequency. The radiation pattern in E-plane at various frequencies have been shown in Fig The radiation pattern of the antenna was measured in anechoic chamber. The crosspolarization level of this antenna is better than 11.4 db as shown in Fig. 9 and 10. Such type of antenna can be useful wireless and mobile applications Fig. 3b Experimental Result of 0 th Iterative Appollian Gasket Antenna with CPW-Fed Fig. 4 Experimental Result of Appollian based Gasket Fractal Antenna Table 1: Measured Resonant Frequencies and Impedance Bandwidth Fig. 3a Simulated Result of 0 th Iterative Appollian Gasket Antenna with CPW - Fed Resonant Impedance BW % BW Frequency 1.52 GHz 1060 MHz GHz 1290 MHz GHz 2640 GHZ 32.6

4 Fig. 5, Radiation pattern of Appollian Gasket Fractal Antenna at 1.07 GHz Fig. 8, Radiation pattern of Appollian Gasket Fractal Antenna at 5.14 GHz Fig. 6, Radiation pattern of Appollian Gasket Fractal Antenna at 1.21 GHz Fig. 9 Cross Polarization of Appollian Gasket Fractal Antenna at f = 1.07 GHz Fig. 7, Radiation pattern of Appollian Gasket Fractal Antenna at 1.6 GHz Fig. 11 Cross Polarization of Appollian Gasket Fractal Antenna at f = GHz

5 V. CONCLUSION Appollian based gasket fractal antenna of compact size with multi-band has been successfully demonstrated. Appollian gasket was constructed with third iteration. The measurement results show good radiation and impedance matching characteristics at all three bands. The multi-band response of this antenna accurs in L-band, C-band to X band. The experimental radiation of the antenna is omnidirection at lower frequency. This antenna is compact, simple to design and easy to fabricate. Antennas of this type can be attractive for GPS, PCS, imaging System and Vehicular radar. ACKNOWLEDGEMENT Authors would like to thanks the Vice Chancellor and Pro-Vice Chancellor (Academics) of Defence Institute of Advance Technology, Girinagar, and Pune for all support and encouragements. They would like to thanks the staff Department of Electronics Engg. and Ph.D students of Microwave and millimeterwave antenna Lab for their support. REFERENCES [1] K. J. Vinoy, Fractal shaped antenna elements for wide and multi-band wireless applications, Thesis, Pennsylvania, Aug [2] C. Puente, J. Romeu, R. Pous, and A. Cardama, On the behavior of the Sierpinski multi-band fractal antenna, IEEE Trans. Antenna Propagat.,vol. 46, pp , 1998 [3] C. Puente, J. Romeu, R. Pous and R. Bartoleme Perturbation of the Sierpinski antenna to allocate operating bands, Electron. Lett., 32, pp , 1996, [4] D. H. Werner and R. Mittra, Frontiers in Electromagnetics IEEE Press, New York, [5] C. Puente, J. Romeu and A. Cardama, The Koch monopole a small fractal antenna, IEEE Transactions on Antennas and Propagation, Nov [6] J. Anguera, Fractal and Broad-Band Technique on Miniaturize, Multifrequency, and high directivity microstrip patch antennas, Ph.D. thesis, UPC, Spains, 2004.