An UWB Planar Inverted-F Antenna for wireless applications T. Chattha, 2M. K. Ishfaq, 3Y. Huang, and 3S. J. Boyes, Dept. of Electrical, Electronics and Telecom.Eng., University of Engineering & Technology (Lahore), Faisalabad Campus, Pakistan, 2Dept. of Telecom. Eng., G. C. University, Faisalabad, Pakistan, 3Dept. of Electrical Eng. & Electronics, University of Liverpool, UK University of Liverpool L69 3GJ, U.K.
[email protected], and
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Abstract —The planar inverted-F antenna (PIFA) is widely used in mobile and portable radio systems due to its excellent features. However, it is not yet employed as an ultra wide band antenna because it was considered a narrowband antenna. This paper introduces an ultra wideband planar inverted-F antenna based on three techniques, which are (a) changes in the widths of feed and shorting plates, (b) addition of an inverted-L shaped parasitic element and (c) addition of a rectangular parasitic element. It is shown that ultra wideband PIFAs with fractional bandwidth of more than 100 % is achieved covering from 3.4 GHz to 10.7 GHz. Simulated and measured results are provided to verify the conclusion.
Index Terms— Antennas, PIFA, planar antennas, input impedance bandwidth
1. INTRODUCTION A considerable research has been done for the development of ultra wideband (UWB) antennas for its high data rates, low power consumption, wide bandwidth and simple hardware configuration in application such as radio frequency identification devices, sensor networks, radar and positioning systems etc.The bandwidth allocated to UWB is from 3.1 GHz to 10.6 GHz by the Federal Communications Commission (FCC) in 2002 [1]. A good amount of printed monopole UWB antennas exist in literature [2-7]. However, the radiation patterns of these antennas are omni-directional. Some UWB applications require antennas with comparatively higher directivity than those of printed monopole antennas. The planar inverted F antenna (PIFA) is now widely used in mobile and portable radio applications due to its simple design, lightweight, low-cost, conformal nature and attractive radiation pattern[8-11]. The PIFA has higher directivity as compared to the planar monopole antennas which makes it more suitable for certain UWB applications. PIFA was generally considered a narrow-band antenna and a significant amount of effort has been made to broaden its bandwidth[12-14].Feik et al showed that diversely shaped feed plates can be used to increase the impedance bandwidth up to 25 % fractional bandwidth [15].
Wg Z
Y
Ground plane
X
W Top plate
Dc1
Wf
Feed plate
tc3
Lg
tc2 h-d
Dc
CL
t Ws
L
tc1 Feed Fig. 1 Geometry of PIFA
3. SIMULATED AND EXPERIMENTAL RESULTS
2. ANTENNA CONFIGURATION The configuration of the PIFA is shown in Fig. 1. The radiating top plate has dimensions of W×L and ground plane
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dimensions areWg×Lg. There is an air substrate of thickness t = 1.0mm between the rectangular ground plane and feed plate. The antenna height is h and the space between the top plate and the substrate is also filled with air (free space). The shorting plate has dimensions of Ws×(h+t) and feed plate has dimensions of Wf×h and shorting plate is placed under the top corner of the top plate. The horizontal distance between shorting and feed plates is Lb. An inverted-L shaped parasitic element is added at a distance Dc from the feed plate. The thicknesses of the parasitic element are tc1 and tc2. The height of the parasitic element is (h+t)-d where d is the vertical distance between the top plate and the element. The horizontal extension of this element is CL. Second parasitic element rectangular in shape is inserted at the upper edge of the ground plane at a distance Dc1 from the shorting plate. The width of this element is tc3 while its height is the same as that of inverted-L parasitic element i.e. (h+t)-d. The PIFA antenna is fed by a coaxial cable through a SMA connector. The simulation software package used is Ansoft’s High Frequency Structure Simulator (HFSS).
The effect of changing the width of feed plate Wf on the fractional bandwidth for Ws = 1 mm is shown in Fig. 2, while the frequency ranges from 1 to 3.5 GHz in which the S11 remains below -10 dB. It is evident that increasing the width of the feed plate increases the fractional bandwidth up
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to a particular value then further increase in the feed plate width only serves to decrease the fractional bandwidth. Therefore an optimum value for the width of feed plate should be selected for achieving the maximum bandwidth. Similarly the effect of changing the width of the shorting plate on the fractional bandwidth is also investigated and the results are shown in Fig. 3 for Wf= 5 mm. It is observed that increasing the width of the shorting plate increases the fractional bandwidth to about 25% and further increases of the shorting plate width results in the decrease of the fractional bandwidth for a given feed plate width. Thus there is also an optimum width for the shorting plate. It is observed that increasing the widths of shorting and feed plates result in the increase of the resonant frequency. In addition, it is also found that the maximum global bandwidth is achieved when the width of the shorting plate width is relatively small [16] which could explain why much wider bandwidths are achieved than in [15].
0.07λ = 3 mm, tc1 = tc2 = tc3 = 0.012λ = 0.5 mm, (h+t)-d = 0.116λ = 5 mm, CL = 0.058λ = 2.5 mm. The simulated and measured results of S11 are shown in Fig. 5.It is seen that the bandwidth achieved by these techniques for S11< -10 dB is extremely broad with a fractional bandwidth of more than 100%, from about 3.4 GHz to about 10.7 GHz with central frequency fc = 7 GHz i.e. λ = 43 mm, which is very close to the entire UWB band.The simulated and measured results are generally in good agreement. Their differences are mainly due to the following factors (a) the cables: which are not included in the simulation but presented in the measurements; b) the connector: which is also not considered in the simulation; (c) The inaccuracy of exact parameters in manufacturing the PIFA as it is made manually in the lab. The lower frequency and first resonance is controlled by the main structure of PIFA, whereas the insertion of inverted-L shaped parasitic element creates a second resonance at 8 GHz and the presence of rectangular shaped parasitic element produces a third resonance around 10.3 GHz (simulated).
Fig. 2 Feed plate width versus fractional bandwidth for Ws = 1 mm Fig. 4 The built ultra wide band PIFA for measurements
Fig. 3 Shorting plate width vs. fractional bandwidth for Wf= 5 mm An UWB PIFA with two parasitic elements (inverted-L shaped and rectangular shaped) is developed as shown in Fig. 4. The parameters for this optimized UWB PIFA antenna are as follows: Wg= 0.43λ = 18.5 mm, Lg= 0.65λ = 28 mm, W = 0.43λ = 18.5 mm, L = 0.22λ = 9.5 mm, h = 0.105λ = 4.5 mm, Wf= 0.198λ = 8.5 mm, Ws = 0.012λ = 0.5 mm, Lb = 0.128λ = 5.5 mm, Dc = 0.012λ = 0.5 mm, Dc1 =
Fig. 5 Reflection coefficient [S11] in dB versus frequency in GHz The simulated 3D radiation pattern (polar plot) of the PIFA antenna with two parasitic elements at 6 GHz is shown in Fig. 6 and the measured 2D radiation patterns of this
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antennaat different frequencies in dB scale are shown in Fig.7 for different planes. The graph of the measuredgain versus the frequency of this UWB PIFA is shown in Figs. 8.
Fig. 7(b) Radiation pattern in dB as a function of θfor azimuth XY plane (θ=90°) for different frequencies Fig. 6 Simulated 3D radiation pattern of UWB PIFA with two parasitic elements at 6 GHz
Fig. 8 Measured peak gain in dB versus frequency in GHz of the UWB PIFA
Fig. 7(a) Rad. patternin dB as a function of θfor elevation XZ plane (Φ=0°) for different frequencies
4. CONCLUSIONS An UWB PIFA antenna is designed fabricated and tested which covers nearly the entire UWB band from 3.4 GHz to 10.7 GHz with a fractional bandwidth of more than 100%. REFERENCES [1] Anon., “FCC first report and order on ultra-wideband technology,” Feb. 2002. [2] S. Y. Suh, W. L. Stutzman, and W. Davis, “A new ultrawideband printed monopole antenna: the planar inverted cone antenna (PICA)”, IEEE Trans. Antennas Propagation, Vol.52, pp.1361-1365, May 2004 [3] I. Makris, D. Manteuffel, R. D. Seager, J. C. Vardaxoglou, “Modified Designs for UWB Planar Monopole Antennas”; Loughbrough Antennas & Propagation Conference 2007, pp.249 – 252, April 2007 [4] X. Chen, J. Liang, P. Li, Guo, L., C.C. Chiau and C.G. Parini, “Planar UWB monopole antennas”. Asia-Pacific Microwave Conference Proceedings Vol.1, pp.4, December 2005. [5] H.G. Schantz, “Planar elliptical element ultra-wideband dipole antennas,” IEEE Antennas and Propagation Society International Symposium, Vol. 3, June 2002, pp. 44.
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[6] K. C. L. Chan, Y Huang and X Zhu, “Planar Elliptical Monopole with CPW Feed for UWB Applications,” Proc. IEEE/ACES Int. Conf., pp.182185, April 2005. [7] J. X. Liang; C. C. Chian; X. D. Chen; C. G. Parini, “Study of a printed circular disc monopole antenna for UWB systems”, IEEE Trans.Antennas propagation, Vol. 53, pp. 3500-3504, November 2005 [8] K. Hirasawa and M. Haneishi, Analysis, Design, and Measurement of Small and Low-Profile Antennas, Artech House, 1992. [9] K. L. Virga, Y. R. Samii, “Low-profile enhanced-bandwidth PIFA antennas for wireless communication packaging”, IEEE transaction on microwave theory and techniques, Vol.45, No. 10, October 1997. [10] P. S. Hall, E. Lee, C. T. P. Song, Planar Inverted-F Antennas, Chapter 7, Printed Antennas for wireless Communications Edited by R. Waterhouse, John Wiley & Sons, 2007. [11] Y. Huang and K. Boyle, Antennas: from theory to practice, John Wiley & Sons, 2008 [12] D. Liu, B. Gaucher, “The inverted-F antenna height effects on bandwidth” IBM T. J. Watson Research Centre, Yorktown Heights, NY10598, IEEE, 2005. [13] F. Wang, Z. Du, Q. Wang and K. Gong, “Enhanced-bandwidth PIFA with T-shaped ground plane,” Electronics Letters, Vol. 40, No. 23, 11th November 2004. [14] P. W. Chan, H. Wong and E. K. N. Yung, “Wideband planar invertedF antenna with meandering shorting strip”, Electronics Letters, 13th March 2008 Vol. 44 No. 6. [15] R. Feick, H. Carrasco, M. Olmos,H. D. Hristov, “PIFA input bandwidth enhancement by changing feed plate silhouette,”Electronics Letters, 22ndJuly,2007. [16] H. T. Chattha, Y. Huang and Y. Lu, “PIFA bandwidth enhancement by changing the widths of feed and shorting plates,” IEEE Antennas and Wireless Propagation Letters, Vol. 8,2009, pp. 637 – 640.
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