A Modified Compact Ultra Wideband Antenna with Band Rejection for WLAN Applications
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In this paper, a circular ultra wideband antenna is considered which comprises of a planar circular patch element on grounded FR4 substrate of 1.6 mm thickness generating the bandwidth of 6.8 GHz. To enable its extensive use in Wireless Local Area Network (WLAN) applications, it is modified by modulating the microstrip line to generate stopband from 5.9 to 9 GHz rejecting the extended C band and X band. The antenna ground plane is then drilled to form holes implementing EBG structures to obtain desired passband characteristics, from 1.97 to 2.65 GHz and 3.12 to 5.86 GHz suitable for WLAN(2.40–2.484/5.150–5.350/5.725–5.825 GHz) applications. The designed antenna shows good passband and stopband characteristics and return loss S11 and nearly omni-directional field pattern over the frequency band of the passband.
KeywordsModulated microstripline EBG Filter UWB WLAN
With the advancing wireless technology, new approaches and procedures of making antenna circuits with enhanced performance are of great importance to any communication system. Wireless Local Area Network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX) and Ulra WideBand (UWB) standards are most sought after in a variety of wireless application areas [1, 2]. Thereby Electromagnetic Band Gap (EBG) and Defected Ground Structures (DGS) for microwave and millimeter wave applications has gained much concern these years, for example microstrip lines incorporating EBG cells on ground plane have supported the improvement in passband-stopband filter characteristics . These features have been used in bandstop or lowpass filter applications to eliminate the unwanted frequencies and to miniaturize microstrip filter structures . This paper aims at simulation of wideband antenna with interference rejection using filter structures in antenna by incorporating a modulated microstrip line which produces a large stopband. The stripline is modified by inserting square patches in it. Then an EBG based structure is formed by etching holes in the ground plane to improve the passband characteristics. It contribute to the research for EBG based microstrip structures to improve the performance in both the passband and the stopband . A different approach for the implementation of filters with EBGs is investigated.
2 Antenna Design and Parameteric Study
3 Results and Discussions
A column of n identical circles is scratched in the reduced ground plane, beneath the microstrip line with n = 4. It reduces the coupling between the transmission line and the ground plane. The radius of the circles is r = 2 mm. The ratio r/d1 represents the filling factor which is indicative of the relative size of the EBG cell to the period of the configuration. To avoid overlapping between any two adjacent circles, it varies from 0 to 0.5 . The optimal value of r/d1 is found to be 0.25 where a good compromise between the stopband and passband performance can be obtained.
In this paper, a UWB circular antenna using Modulated microstripline and EBG structures is proposed and fabricated to be used in WLAN applications. The antenna creates a stopband from 5.9 to 9 GHz. It also provides permissible return loss in the frequency range from 1.92 to 5.9 GHz. The rejected band is obtained by integrating a Modulated microstripline that resonates at the required rejection frequency band with the circular EBG structures drilled in the ground plane of antenna. The measured data of the antenna matches well with the corresponding simulated results. Moreover it provides VSWR less than 1 for its working frequencies and almost omnidirectional patterns, over an entire UWB frequency band apart from the rejected band.
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