Abstract' In this paper compact ultra-wideband (UWB) printed microstrip antenna with dual band-notched characteristics is presented. The antenna is constructed on an FR-4 epoxy substrate with thickness of 1.6 mm and 'r =4.4. The antenna uses CSRR slot and an EBG structure to create dual band-notched characteristics in, 3.3 - 3.7 GHz for WiMAX and 5.15-5.8 GHz for WLAN, respectively. Surface current distributions are used to show the effect of these slots. The antenna shows broad bandwidth and good omnidirectional radiation patterns in the pass band, with a compact size of 30x30mm2. The proposed antenna operates over 3.1 to 13 GHz for VSWR < 2. All simulations in this work were carried out by using the electromagnetic software Ansoft HFSS 13. This antenna has advantages in simple design, wide bandwidth, and good band-notch characteristic, compact in size and easy in fabrication. Simulated and measured results of the proposed antenna will be presented.
Keywords' EBG antenna, UWB antenna, band notched antenna, CSRR antenna, Microstrip antenna
AFTER declaration by Federal communication commission (FCC) of unlicensed radio frequency band 3.1-10.6 GHz for commercial use, ultra wideband (UWB) has received great attention from academics and industries of telecommunication . In recent years researchers have given more attention to improve the UWB antennas impedance bandwidth, radiation patterns, gain, matching characteristics and to decrease the size of the antenna. UWB has attractive merits which drawn the most researchers attention, such as compact size, low cost, resistant to severe multipath and jamming, ease of fabrication, and good omnidirectional radiation characteristics . However, the ultra-wideband systems are very sensitive to electromagnetic interferences with exciting narrowband wireless communication systems and X-band satellite communication system, it is necessary to design antennas with multiband filtering characteristics to avoid interferences with applications working in this band. For instance, Worldwide Interoperability for Microwave Access (WiMAX) operating in 3.3-3.6 GHz band (IEEE 802.16), wireless local area networks (WLAN) operating in 5.15-5.825 GHz band (IEEE 802.11a), and X-band satellite communication system operating in 7.2-8.4 GHz band (7.25-7.745 GHz for uplink and 7.9-8.395 GHz for downlink). These bands could be rejected with three bandstop filters in UWB but this approach will increase the complexity of the system. Therefore it is necessary to design the UWB antenna with band notched characteristic to reduce the complexity of the system and make it cost effective.
To solve the above problems, make antenna with notched band characteristics, different methods have already been proposed and presented to design UWB with band notched characteristics. Usually, people used mainly two methods these include different types of slots on the radiating patch or on the ground plane, use of split-ring resonators, tuning stubs, meandering, folded strips, resonated cells on CPW, EBG structure etching on patch/ground plane [3-16]. For example, etching of U slot [3-4], V- shaped slot , C- shaped slot , S- shaped slot , a quasi-complementary split ring resonator (CSRR) in fed line , a quarter- wavelength tuning stub in a large slot on the patch , or compact folded stepped impedance resonators (SIRs) or capacitively loaded loop (CCL) resonators in fed [10-11], a parasitic slit along with tuning stub used , C shaped slot on patch and L shaped stub on ground , semi-circular slot on patch , rectangular slots on patch , M-EBG .
In this paper, we propose a compact UWB planar microstrip antenna with dual notched bands for 5.1-5.8 GHz band (WLAN) and 3.3 - 3.6 GHz (WiMAX) using half wave CSRR slot on patch and inverted L shape EBG single cell. The complete antenna size is 30x30 mm2. The proposed antenna has used both methods to create dual notch band.
II. ANTENNA DESIGN AND ANALYSIS
The geometry and configuration of the proposed antenna optimized with the Ansoft HFSS 13 is shown in Fig. 1. This antenna is printed on the FR-4 substrate with thickness of 1.6 mm, relative dielectric constant of 'r = 4.4, and loss tangent of 0.02. The proposed antenna is fed by a microstrip feeder, and the width of the microstrip feed line is 2.8 mm to achieve 50-' characteristic impedance. There is an inverted L shaped EBG ground cell and a Circular split ring resonator cut on radiating patch shown in Fig.1. A circular split ring resonator was cut on radiating patch to create notch in WiMAX band, which is about a quarter wavelengths (??g/2) calculated at 3.5 GHz in the WiMAX band. CSRR provides notch of 3.3-3.6 GHz for WiMAX applications. For notch at higher frequency we have used a grounded inverted L shaped EBG cell that provides a notch band for WLAN applications in 5.1-5.8 GHz band. The total length of CSRR is 9 mm, which is approximately equal to the ??g/2 calculated at 3.5 GHz for WiMAX applications. The lengths of CSRR and resonant frequency have been calculated from the following equations.
Leq = 2'r-g (1)
The value of g is 5.5 mm optimized to create notch at WiMAX band. The optimized dimension of the proposed antenna has been presented in table 1.
Fig. 1. (a) Front view of Proposed Antenna (b) Back view of Proposed Antenna
Fig.2. Primary antenna (UWB)
Optimized dimension of proposed antenna have been presented in table.1 that also show that proposed antenna ground is a partial ground.
Optimized dimensions of proposed antenna
Variable W L R R1 R2 g
Size (mm) 30 30 8.3 5.8 4.9 5.5
S Lf Wf Wg Lg Wg1 Lg1
0.6 11.8 2.8 30 11 5 4
To achieve the dual band notch characteristic through proposed antenna, we first cut a CSRR slot on primary antenna shown in Fig.2, which provides the UWB band. The return loss (S11 in dB) and VSWR due to the primary antenna, due to the CSRR slot only, due to the EBG and the proposed antenna have been presented by Fig.3 and Fig. 4 respectively. From Fig. 3 and Fig. 4, we can see that CSRR slot provides a single band notch characteristic in UWB band for WiMAX Applications, where as EBG provides a single band notch at WLAN band. Now to achieve the notch at higher frequency we have used inverted L shaped EBG cell on primary antenna, which operating in UWB band without any notch. From Fig. 3 and Fig. 4, it can be seen that a single notch at frequency band 3.3-3.6 GHz and 5.1-5.8 GHz provides by CSRR slot & EBG cell respectively. Now to achieve the dual notch band in UWB for WLAN band and WiMAX band, we have combined CSRR and EBG on radiating patch. The returnloss and VSWR of combined slots on radiating patch have been presented in Fig.3 and Fig. 4 respectively.
Fig.3. Return loss of proposed antenna
Fig.4. VSWR of Proposed antenna
Length of EBG namely Lg1, Wg1 & S were varied with a range of values and results are presented. Gap between antenna feed line and EBG structure play a great role to create band notch characteristic, Fig.5 & 6, shows the effect of gap variation on the band notch characteristics. Variation in return loss and vswr of optimized gap have been shown in Fig.5 & 6, respectively.
From Fig.5 & 6, it can be seen that with the gap of S varies from 0.3 mm to 0.8 mm, except 0.6 mm we were not able to achieve our desired notch band. we have achieved desired notched band with the proposed space of 0.6 mm.
Fig.5. Return loss variation with gap distance
Fig.6. VSWR variation with gap distance
Length of EBG structure namely Lg1 & Wg1 has been optimized. The effect of variation in length namely Lg1 on return loss and vswr has been shown in Fig.7&8, respectively. From Fig.7&8, we can see that proposed length of the EBG at 4 mm provides desired band notch with width of Wg1 = 5mm.
Fig.7. Return loss variation for Lg1 with Wg1=5mm
Fig.8. VSWR variation for Lg1 with Wg1=5mm
Width of EBG Wg1 has been optimized. The effect of variation in length namely Wg1 on return loss and vswr has been shown in Fig.9&10, respectively. From Fig.9&10, we can see that proposed length of the EBG at 5 mm provides desired band notch with length of Lg1 = 4mm.
Fig.9. Return loss variation for Wg1 with Lg1=4mm
Fig.10. VSWR variation for Wg1 with Lg1=5mm
In order to observe the effects of CSRR slot and EBG cell in getting the notched bands, the surface current distributions on the radiating patch of the proposed antenna at three different frequencies are shown in the Fig.11. At a passband frequency of 4.5 GHz i.e. outside the notched band, the distribution of the surface current is uniform shown in Fig.11. (a). whereas in Fig. 11 (b-c), have observed stronger current distributions concentrated near the edges of CSRR slot and EBG at the center frequency of the first notched band 3.5 GHz, and the second notched band 5.5 GHz, respectively. These clearly show the positive effects of the slots upon obtaining the band notched characteristics.
(a) (b) (c)
Fig. 11. Current density distribution over patch (a) 4.5 GHz, (b) 3.5 GHz, (c) 5.5 GHz
III. RESULT AND DISCUSSION
Simulated result of proposed antenna has been shown in Fig.12 & 13. The antenna with CSRR slot and EBG successfully exhibits dual notched bands of 3.3 - 3.6 GHz, maintaining broadband performance from 3.1 to 1 GHz ( includes UWB frequency band) with VSWR less than 2. The simulated radiation patterns at 3.5, 5.5, 5.5 and 7.5 GHz have been shown in Fig.14. (a) - (c), respectively. At the passband frequencies out of the notched bands 7.5 GHz, the antenna displays good omnidirectional radiation patterns in the H-plane and dipole like radiation patterns in E- plane as shown in Fig.14.(c). Meanwhile, at notched band frequencies (3.5 and 5.5 GHz) the antenna displays distorted and unstable radiation patterns as shown in Fig.14. (a) & (b). The calculated peak gain of the proposed antenna is shown in Fig.15. Characteristic of proposed antenna as return loss and vswr shown in Fig. 16 as combined.
Fig. 12. S11 Vs frequency
Fig. 13. VSWR Vs frequency
Fig.14. E-H field pattern of proposed antenna (a) 3.5 GHz (b) 5.5 GHz
(c) 7.5 GHz
Fig. 15. Peak gain Vs frequency graph of proposed antenna
Fig. 15. Return loss and vswr Vs frequency graph of proposed antenna in combined form
A compact dual band notched UWB antenna is presented in this letter. This antenna has simple structure and compact size of 30x 30 mm 2 , which is easy to be integrated in miniature devices. Proposed antenna covers frequency band from 3.1 to 13 GHz, where simulated results are good and will be compared with measured result. To prevent interferences with WLAN and WiMAX, two band rejection structures are selected to produce sharp rejection. Results & analysis of this antenna indicates that it is applicable in miniature devices, simple design & compact size as added advantage. Surface current distributions were used to show the effect of these slots in getting the notched bands.
This section will be completed after measurement of Antenna.
 First report and order, Revision of part 15 of the commission's rule regarding ultra-wideband transmission system FCC 02-48, Federal Communications Commission, 2002.
 Z. N. Chen, 'UWB antennas: From hype, promise to reality,' in IEEE Antennas Propag. Conf., 2007, pp. 19'22.
 W.-S. Lee, K.-J. Kim, D.-Z. Kim, and J.-W. Yu, 'Compact frequency notched wideband planar monopole antenna with an L-shaped ground plane,' Microw. Opt. Technol. Lett., vol. 46, no. 4, pp. 340'343, 2005.
 F. Fan, Z. Yan, T. Zhang, and Y. Song, 'Ultra-wideband planar monopole antenna with dual stopbands,' Microw. Opt. Technol. Lett., vol. 52, no. 1, pp. 138'141, 2010.
 Y. Kim and D.-H. Kwon, 'CPW-fed planar ultrawideband antenna having a frequency band notch functions,' Electron. Lett., vol. 40, no.7, pp. 403'404, 2004.
 Q.-X. Chu and Y.-Y. Yang, 'A compact ultrawideband antenna with 3.4/5.5 GHz dual band-notched characteristics,' IEEE Trans. Antennas Propag., vol. 56, no. 12, pp. 3637'3644, Dec. 2008.
 S.-W.Qu, J.-L. Li, and Q. Xue, 'Aband-notched ultrawideband printed monopole antenna,' IEEE Antennas Wireless Propag. Lett., vol. 5, pp. 495'498, 2006.
 W. T. Li,X.W. Shi, and Y. Q. Hei, 'Novel planar UWBmonopole antenna with triple band-notched characteristics,' IEEE Antennas Wireless Propag. Lett., vol. 8, pp. 1094'1098, 2009.
 K. S. Ryu and A. A. Kishk, 'UWB antenna with single or dual band notches for lower WLAN band and upper WLAN band,'IEEE Trans. Antennas and Propag., vol. 57, no. 12, pp. 3942'3950, Dec. 2009.
 Y. Sung, 'UWB monopole antenna with two notched bands based on the folded stepped impedance resonator,' IEEE Antennas Wireless Propag. Lett., vol. 11, pp. 500'502, 2012.
 C.-C. Lin, P. Jin, and R. W. Ziolkowski, 'Single, dual and tri-band-notched ultra-wideband (UWB) antennas using capacitively loaded loop (CLL) resonators,' IEEE Trans. Antennas Propag., vol. 60, no. 1, pp. 102'109, Jan. 2012.
 Rezaul A., M.T. Islam, and A.T. Mobashsher 'Design of a Dual band notch UWB slot antenna by means of simple parasitic slits,' IEEE Antennas Wireless Propag. Lett., vol. 12, pp. 1412'1415, 2013.
 Peng Gao, L.X., J.Dai, S.He and Y.Zheng, 'Compact Printed wide slot UWB antenna with 3.4/5.5 GHz dual band-notched characteristics,' IEEE Antennas Wireless Propag. Lett., vol. 12, pp. 983'986, 2013.
 D. T. Nguyen, D. H. Lee, and H. C. Park, 'Design and analysis of printed triple band-notched UWB antenna,' IEEE Antennas Wireless Propag. Lett., vol. 10, pp. 403'406, 2011
 D. T. Nguyen, D. H. Lee, and H. C. Park, 'Very compact printed triple band-notched UWB antenna with quarter-wavelength slots,' IEEE Antennas Wireless Propag. Lett., vol. 11, pp. 411'414, 2012.
 Hao Liu and Ziqiang Xu, 'Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic Bandgap Structure' Hindwi Publishing Corporation. Vol.2013, articl.id 917965.