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A Compact Ultra Wideband Antenna with Dual. Band-Notched Design. Y.E. Jalil*, C.K. Chakrabarty. Centre for RF and Microwave Engineering, Department of.
A Compact Ultra Wideband Antenna with Dual Band-Notched Design Y.E. Jalil*, C.K. Chakrabarty

B. Kasi

Centre for RF and Microwave Engineering, Department of Electronics and Communication Engineering Universiti Tenaga Nasional Kajang, Selangor, Malaysia [email protected], [email protected]

Department of Electrical and Electronics Engineering Kuala Lumpur Infrastructure University College Kajang, Selangor, Malaysia [email protected]

Abstract— The coexisting issue between ultra-wideband (UWB) system and narrow band system has been a major concern for quite a while. A filtering property is required in a wideband system in order to avoid the potential interference from other established narrow band system. Therefore, an UWB antenna with notch band function is highly sought after to eliminate the interfering signals. This paper presents a compact UWB antenna integrated with dual band notched and desirable gain characteristics. The proposed antenna consists of an octagon shaped patch with a truncated ground plane that is fed by a 50 Ω microstrip line. By inserting two altered H-shaped slots on the proposed radiator, dual band-notch at the targeted WiMAX frequency band of 3.3 to 3.6 GHz and WLAN frequency band of 5.1 to 5.8 GHz are created. The proposed antenna is successfully designed and simulated showing good impedance matching from 2.8 GHz to 11 GHz. Furthermore, the proposed antenna has a compact size of 26 × 32 mm2. Keywords-frequency-notched; wideband (UWB)

I.

microstrip

antenna;

ultra

INTRODUCTION

The Federal Communications Commission (FCC) authorized the unlicensed use of a bandwidth of 7.5 GHz (from 3.1 GHz to 10.6 GHz) for ultra wideband (UWB) wireless communications in 2002 [1]. Since then, UWB technology has been rapidly advancing as a promising high data rate wireless communication technology for various applications. In spite of having allocated a wide frequency range, UWB devices suffer the consequences of having to share the spectrum with a number of other established narrowband applications. For instance, the frequency bands of UWB communication system include the IEEE 802.16 WiMAX system operating at 3.3 – 3.6 GHz and the wireless local area network (WLAN) for IEEE 802.11a operating at 5.15 – 5.825 GHz. The operation of UWB radios is almost "invisible" for other applications attributable to the significantly lower emitted power from UWB radios (EIRP -41.3 dBm/MHz) [2]. Nevertheless, strong signals from other narrowband systems may cause severe electromagnetic interference that could affect the overall performance of UWB communication systems in terms of increasing pulse distortion and bit error rate. An antenna with wideband impedance matching is one of the key components in the UWB system. With the aim to

overcome this unwanted problem, an antenna incorporated with filtering property is required in an ultra-wideband system. However, the addition of filters will increase the size, weight and complexity of the UWB system and thus lead to increase in cost [3]. Therefore it is desirable to design UWB antennas with band-notched function in the affected frequency bands. Several studies have been reported by numerous researchers on diverse antenna geometries, design methods and structures in order to achieve band-notched features. One of the most popular methods is by embedding complementary resonance elements into either the radiating plane, ground plane or the feed line of the antenna. Some examples of this technique are by inserting slot in the ground plane [4], or embedding slots with various shapes in the radiating patch [5], or utilizing capacitively loaded loops [6], or inserting strip in the slot [7], or using microstrip open loop resonator [8]. Nevertheless, most of the methods proposed have only managed to create a single notched band and unable to provide sufficient rejection bandwidth in the targeted narrowband operating frequency range. In contrast, Xue-jie Liao et al proposed an UWB with dual band-notched [9]. The design is based on a planar circle-shaped radiation patch with an ellipseshaped slot on the front side. A partial ground plane is printed on the back surface of the antenna. The dual band-notched is created by attaching a parasitic strip to the bottom layer of the antenna and etching a pair of hook-shaped slots on the ground to form a defected ground plane. Both design methods are suitable to be integrated to an antenna in order to produce narrow frequency notches within the UWB range. Nevertheless, the authors used two totally different structures and one of the structures caused an insufficient rejection bandwidth. Consequently, some useful frequencies may have been wasted and can affect the antenna performances in time domain. In this paper, an octagon shaped UWB antenna with dual band-notched characteristic is proposed. The antenna has a wideband impedance matching from 2.8 GHz to 11 GHz. By inserting two altered H-shaped slots on the radiating patch, The targeted frequency band-notched at 3.3 – 3.6 GHz and 5.0 - 5.8 GHz is achieved. The presented design structure of the bandnotched mechanism can be easily extended to other planar UWB antennas. The outline of this paper is as follows. The geometry of the proposed antenna is presented in section II.

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Details of the simulation results and analysis are described in Section III. Finally, the conclusions are summarized in Section IV. II.

ANTENNA CONFIGURATION AND DESIGN

The geometry and configuration of the proposed UWB antenna is depicted in Fig. 1. The antenna is located in the x-y plane and the normal direction is the z-axis. This proposed antenna design consists of an octagon-shaped radiator fed by a microstrip line printed on a partial grounded substrate. The microstrip line feed is designed to match a 50 Ω characteristic impedance. The impedance matching is enhanced by correctly adjusting the dimension of the feeding structure and the patch size. In addition, the design and optimization of the ground plane for a compact UWB antenna is critical for the overall antenna performance [2]. Therefore, to ensure smooth transitions from one resonant mode to another, both the radiating plane and the ground plane have tapered shapes at both ends. Apart from that, a rectangular slit is added on top of the ground plane to further enhance the impedance bandwidth of the antenna. W

Wp

L

Le

Lp We

Wf Lf

The simulation of the proposed antenna model design as well as the optimization of the designed parameter values is performed using CST Microwave Studio. The optimization was carried out to achieve the best impedance bandwidth. To find the most optimum values, parametric study for different parameters of the antenna has been performed. This is done by varying one parameter while maintaining other parameters constant. As a result, this antenna (will be referred to as antenna 1 in this paper) has a good impedance bandwidth covering the entire UWB frequency range with satisfactory radiation pattern. The proposed antenna is printed on a standard FR4 substrate with a dielectric substance of 4.3, a loss tangent of 0.025 and with thickness of 1.6 mm. The final optimized parameter values are W = 26 mm, L = 32 mm, Wp = 20 mm, Lp = 18 mm, Wf = 3.92 mm, Lf = 12 mm, We = 12 mm, Le = 8 mm, Wt = 5.5 mm, Lt = 2, Wx = 3.4 mm, Lx = 3.65 mm and Lg = 11.3 mm. The conventional and easy way to achieve band-notched function is by embedding slots on the radiating patch or the ground plane which results in the changed in the surface current distributions. In this paper, two mirrored H-shaped slots are etched on the proposed UWB antenna. The geometry and dimensions of the antenna with band-notched design (will be referred to as antenna 2) is illustrated in Fig. 2. The first notch at 3.5 GHz is produced by the outer H-shaped slot while the inner slot which is the inverted H-shaped slot is introduced to achieve the notch at 5.5 GHz. The previously optimized design parameters of the UWB antenna need no additional retuning work when the band-notched design is applied. In general, the design concept of the notch function is to adjust the total length of the slot to be approximately half-wavelength at the desired unwanted frequency [10]. As presented in [10], the notch frequency given the dimensions of the band-notched feature can be postulated as in equation (1)

f

(a)

notch

c

= 2L •

ε eff

(1)

Where L is the total length of the slot, εeff is the effective dielectric constant and c is the speed of light.

t Wh1 Lh1

We

Lh2

y

Wt Lt

Wh2

Lx Wx

x

Lg

(b) Figure 1. Geometry of the proposed antenna 1 (a) front (b) back

Figure 2. Geometry of the proposed antenna 2 - with H-shaped slots

Equation (1) is used to acquire the initial total length of a single H-shaped slot at the beginning stage of the design. The analysis of the notched design with different widths and lengths of the slots are performed to get the optimized parameters. The final design parameters for the altered Hshaped slots are Lh1 = 6.7 mm, Lh2 = 8.8, Wh1 = 6 mm, Wh2 = 8.8 mm and t = 0.6 mm. III.

SIMULATED RESULTS AND ANALYSIS

The simulated return loss of the proposed antenna with and without the notched bands is shown in Fig. 3. It is observed that, the calculated return loss curve for antenna 1 is less than 10 dB from 2.8 GHz to beyond 11 GHz. The result indicates that the impedance bandwidth of the antenna is more than 8.2 GHz, covering the entire UWB frequency range. Dual bandnotched characteristic can be seen from the return loss curve for antenna 2. It clearly exhibits two notched bands of 3.3 - 3.6 GHz and 5.1 - 5.8 GHz. The comparison of simulated VSWR for the proposed antenna design with and without H-shaped slots is demonstrated in Fig. 4. It is evident that the addition of the slots onto the radiating plane is indeed introduced the desired filtering property. The targeted WiMAX and WLAN band have been successfully blocked out by the band-notched antenna with VSWR > 2 while still maintains good impedance matching at other frequencies in the UWB band.

Figure 4. Simulated VSWR of the proposed antennas

Fig. 5 illustrates the surface current distributions at three different frequencies of 3.5 GHz, 5.5 GHz and 7.5 GHz. These frequencies are selected to discuss the mechanism of frequency rejection by using current distributions along the radiating element. This analysis is required in order to gain a better understanding on the antenna operation. It can be observed that at the targeted notch frequency of 3.5 GHz and 5.5 GHz, the current distribution is mainly concentrated on the both arms of the H-shaped slots as can be seen in Fig. 5(a) and (b). Meanwhile the current on the radiating elements (the resonator and the feed line) are weak. It indicates that most of the energy supplied to the radiating patch are intercepted by the slots causing dual band notch at these frequencies. The currents cancel perfectly in the center of the radiating patch leading to a null. Consequently, the antenna could not radiate and the frequency rejection is achieved. In contrast, the current distribution is primarily concentrated around the periphery of the radiating patch and the microstrip feed line at the frequency in pass band as shown in the Fig. 5(c). There is very little current flow within the interior of the resonator. As a result, the antenna is able to radiate electromagnetic wave at those frequencies. It also implies that the altered H-shaped slots do not have any significant effect on the antenna performance at pass band.

Figure 3. Simulated return loss of the proposed antennas

(a)

(c) Figure 5. Surface current distributions at (a) 3.5 GHz (b) 5.5 GHz (c) 7.5 GHz

The variation of gain versus frequency for the notched antenna design is shown in Fig. 6. It can be significantly observed that the gain decreases drastically at the both targeted notch bands. The expected gain reduction is confirmed by the computed peak gain value of –2.5 dBi at 3.5 GHz and -3.7 dBi at 5.5 GHz . It also validates the antenna’s ability to provide a satisfactory level of filtering to signal frequencies within the rejection bandwidth. Apart from that, it can be observed that the gain starting to descend at the higher frequency band which is expected as it is one of the common feature of UWB monopole planar antenna [11].

(b)

Figure 6. Simulated gain of the proposed antenna 2

IV.

CONCLUSION

This paper proposed a compact UWB microstrip antenna design for UWB applications. The antenna is capable of achieving an input impedance bandwidth from 2.8 to beyond 11 GHz. A couple of altered H-shaped slots are introduced on the radiating patch to create dual notched band from 3.3 to 3.6 GHz and from 5.1 to 5.8 GHz. This proposed antenna is suitable for numerous UWB applications and can be used to avoid interference from from the WiMAX and WLAN systems when they coexist with UWB services.

REFERENCES [1] [2]

[3]

[4]

FCC, First Report and Order 02-48. February 2002. S. Nikolaou, A. Amadjikpe, J. Papapolymerou, and M. M. Tentzeris, "Compact Ultra Wideband (UWB) Elliptical Monopole with Potentially Reconfigurable Band Rejection Characteristic," Asia Pacific Microwave Conference (APMC), pp. 1 - 4, 2007. T. G. Ma and S. K. Jeng, “Planar miniature tapered-slot-fed annular slot antennas for ultra-wideband radios,” IEEE Transactions on Antennas and Propagation, vol. 53, pp. 1194 – 1202, 2005. J. William and R. Nakkeeran, "CPW-Fed UWB slot antenna with band notched design," Asia Pacific Microwave Conference (APMC), pp. 1833 - 1836, 2009.

[5]

T. Li, H. Q. Zhai, C. Zhu, L. Li, C. H. Liang, and Y. F. Han, “Design and analysis of compact printed dual band-notched ultrawideband (UWB) antenna,” Journal of Electromagnetic Waves and Applications, vol. 27, pp. 560 – 571, 2013. [6] S. Nikolaou, M. Davidovic, M. Nikolic, and P. Vryonides, "Resonator type and positioning study for the creation of a potentially reconfigurable frequency notch in a UWB antenna return loss," Proceedings of the 5th European Conference on Antennas and Propagation (EUCAP), pp. 350 - 353, 2011. [7] D. Hongwei, H. Xiaoxiang, Y. Binyan, and Z. Yonggang, "Compact band-notched UWB printed square-ring monopole antenna," 8th International Symposium on Antennas, Propagation and EM Theory (ISAPE), pp. 1 - 4, 2008. [8] J. R. Kelly, P. S. Hall, P. Gardner, and F. Ghanem, "Integrated narrow/band-notched UWB," Electronics Letters , vol. 46, no. 12, pp. 814 - 816, 2010. [9] L. Xue-jie, Y. Hong-chun, and H. Na, "An improved dual band-notched UWB antenna with a parasitic strip and a defected ground plane," International Symposium on Intelligent Signal Processing and Communication Systems (ISPACS), pp. 1 - 4, 2010. [10] C. Qing-Xin and Y. Ying-Ying, "A Compact Ultrawideband Antenna With 3.4/5.5 GHz Dual Band-Notched Characteristics," IEEE Transactions on Antennas and Propagation, vol. 56, pp. 3637 - 3644, 2008. [11] J. R. Kelly, P. S. Hall, and P. Gardner, "Band-Notched UWB Antenna Incorporating a Microstrip Open-Loop Resonator," IEEE Transactions on Antennas and Propagation, vol. 59, pp. 3045 - 3048, 2011.