A Miniaturized UWB Microstrip Antenna Structure

Transcription

1 A Miniaturized UWB Microstrip Antenna Structure Ahmed Abdulmjeed 1, Taha A. Elwi 2, Sefer Kurnaz 1 1 Altinbas University, Mahmutbey Dilmenler Caddesi, No: 26, Bağcılar-İSTANBU 2 Department of Communication, Al-Mammon University College, Baghdad, IRAQ Abstract: This paper focuses designing of an ultra-wide-band (UWB) printed circuit antenna of enhanced performance in terms of gain and radiation patterns with the aid of metamaterial (MTM) structures. The patch is formed as a miniaturized open mouth flower backed with a partial ground plane to provide a significant enhancement in the antenna bandwidth. To provide a stable antenna radiation pattern over the entire frequency band, a MTM structure is introduced at the edge of patch structure. The proposed MTM unit cell is constructed from three arrays of H- resonators. Such arrays are provided to focuses the antenna radiation patterns toward the endfire of the antenna. The MTM characterizations in terms of effective refractive constitutive parameters are retrieved within the frequency band of interest. The numerical simulations are conducted using CST MWS and HFSS software packages to arrive to the optimal antenna design based the proposed MTM structure. Lastly, the optimum patch antenna scheme is fabricated and tested experimentally for confirmation. Key words UWB, MTM, partial ground. 1. Introduction In the last two decades, wireless communication technologies have changed our lives [1]. Without counting the home and office areas, the wireless handsets free us from the short phone leashes and provide us more freedom to communicate with others at any-time and in any-place [2]. For example, local-networks of wireless technologies help users to obtain internet access with no the need for cables with great services quality [1]. In1G mobile network, the analoguecommunication was allowed, while,2g was realized by the digital-communication [3]. 3G provided video telephony, internet service, video and music download, and digital-voice communication [4]. In 4G, well defined audio and video services were on-demand provided [5]. Recently, more efforts were conducted on the mobile personal wireless devices to deliver a steadfast wireless connection between personal computers and mobile handsets within a near zone [6]. Moreover, such technology accomplishes a fast data exchange and packing between handsets [7]. This technology requires a high bit rate for the best band based partial Additive- White-Gauss`ian-Noise (A.W.G.N.) network that is correlated to the signal/noise-ratio (S.N.R.) and band limitation by Shan`non formula [8]: Where C is the full data rate to be transmitted over the channel and B is the channel width Eq.(1) indicates the channel capacity could be increased rabidly through increasing the channel-bandoccupation or transmitted-power[9]. However, the transmitted-power, i.e. SNR, must not be (1)

2 increased significantly because most handsets are powered by charge-able battery and provide interference consolation [10]. Therefore, increasing the bandwidth is a feasible key to achieve a high bit rate [8], in which, the FCC marketed the operation of the UWB technology [3]. Therefore, the UWB technology became a very promising wireless technology to transform a high bit rate that enables personal network industry to further innovations with great service features [4]. 2. An UWB Antenna based MTM Structure Design In this section, a numerical study based on Computer-Simulation-Technology/Microwave- Studio (CST MWS)algorithms [11] is invoked to improve the antenna performance and the MTM characterizations. In the first part of this section, the antenna structure is optimized to provide the maximum antenna bandwidth match with maximum gain. Next, the MTM is designed and characterized numerically in terms of S-parameters. Then, the antenna structure is integrated to the MTM to realize obtained enhancements on the antenna performance. A partial ground plane microstrip antenna based on a flower of an open mouth cut is designed as an UWB printed circuit antenna. The suggested antenna shows a bandwidth from 2.4GHz up to10ghz.the obtained gain of the proposed antenna is found to change from 4.5dBi up to 5.9dBi.The antenna patch structure, the radiating element, is fed with a 50Ω micro strip line. The patch layer is etched on an FR-4 substrate of 30mm 60mm with 1mm thickness. The partial ground plane is introduced to obtain the maximum bandwidth coupling over the entire band of interest. Therefore, the antenna radiation patterns would be mostly scattered toward different directions that limits the antenna use in portable and compact handsets devices. In Figure 1, the antenna design based on MTM structure is presented.

3 Figure 1: Antenna design details in mm; (a) MTM based H-resonator, (b) back view, and (c) front view. The microstrip line structure is constructed from a rectangular copper trace width varies from 1mm up to 2mm mounted on the FR-4 substrate. 3. An UWB Antenna based MTM Structure Design The unit cell structure is characterized in terms of S-parameters to retrieve the constitutive parameters in terms of relative permittivity (ε r ) and relative permeability (μ r ). As seen in Figure 2, the S-parameters are evaluated from CST MWS, than, they are compared the HFSS results. This comparison is performed to validate the obtained results from the CST MWSsoftware package.

4 Figure 2: The evaluated S-parameters from both numerical and analytical techniques. Now, the ε r and μ r spectra of the proposed MTM are retrieved using Nicholson-Ross-Weir formulations [14] as seen in Figure 3. It is found that the proposed unit cell shows no negative part, however, the unit cell shows ε r =8 at 3.8GHz and 7 at 7.5GHz, while, the value of μ r is found to be 6.7 at 3.6GHz and 8 at 7.8GHz. 4. The Optimal Antenna Design Figure 3: The retrieved constitutive parameters. The antenna structure is based on a partial ground plane to obtain significant bandwidth enhancements. In Figure4, the ground plane length effect on the matching impedance is realized with the S 11 spectra. It is found that the antenna shows the best matching bandwidth at 7mm from the antenna center. This is due to the effects of fringing from the ground plane edges with respect to the patch edges.

5 Figure 4: S 11 spectra with different ground plane lengths. The effect of introducing the MTM structure arrays to the antenna resultsare evaluated by considering the spectrum ofs 11 and gain. It is found that the antenna shows a wideband from 2.45GHz up to 10GHz with excellent matching, S11 <-10dB, as seen in Figure5. Figure 5: S 11 spectra with different MTM arrays. 5. Antenna Performance Validation and Measurements The proposed antenna performance is validated numerically before realize the prototype fabrication and perform the experimental measurements. Then the proposed antenna is fabricated using chemical etching processing. The fabricated antenna is shown in Figure 6(a) with MTM structure. The numerical validation is conducted with HFSS software package [15] to evaluate the S 11 spectrum and the radiation patterns at 2.45GHz and 5.8GHz. As seen in Figure 6(b), the obtained results from the CST MWS software package agree excellently with those obtained from the HFSS simulations. The proposed antenna is found that provides an excellent matching-band, S 11 <-10dB, for the entire band from 2.38GHz up to 10GHz. When the experimental measurements are conducted with a Vector Network Analyzer (VNA) of Vector star MS4642A Series, the antenna shows excellent matching with entire band from 2.4GHz up to 10GHz.

6 Figure 6: (a) The fabricated prototype and (b) Comparison of the simulated S 11 spectra relative to the measurement. The antenna 2D radiation-patterns are evaluated, based on CST MWS and HFSS, at two frequency bands of 2.45GHz and 5.8GHz only for Wi-Fi applications. The obtained antenna gain is found about 4.4dBi at 2.45GHz and 5.4dBi at 5.8 GHz from both of the software packages. This gain enhancement as motioned previously is attributed to the introduction of the MTM structure. The antenna 2D radiation-patterns are presented in Figure 7. Finally, the radiationpatterns of the fabricated prototype are measured inside a microwave anechoic-chamber at the E- and H-planes. The measurements are performed after calibrating the free space losses inside the chamber using the VNA. Later on, the proposed antenna is mounted on a rotary mount, while, the

7 reference antenna is located in the line of sight from the antenna under the test. The simulated and measured results are excellently agreed at the two frequency bands of interest. Figure 7: Radiation patterns measurement in comparison to simulated results; (a) E-plane at 2.45GHz, (b) H-plane at 2.45GHz, (c) E-plane at 5.8GHz, and (d) H-pane at 5.8GHz. 6. Conclusions In this work, an UWB miniaturized microstrip antenna based of slotted flower profile has been designed, simulated, and implemented on a range of frequency from 3GHz to 10GHz. The purpose of this design is to illustrate the effect of adding the MTM cells in H-resonators shapes for bandwidth and enhancements. The resulted antenna has the advantage of small dimensions (60mm 30mm) and a bandwidth smaller than that required by the standard FCC UWB. The UWB antenna based MTM is altered to enhance its specifications and produce a wideband frequency range which can be used for biomedical applications. The design has been optimized and verified using CST MWs and HFSS software packages.then, it has been fabricated and tested successfully. The measurements of the fabricated antenna are almost similar to the simulation results but they are not typically the same due to the limited fabrication defects. For the proposed UWB antenna based MTM, the radiation patterns within the operating frequency bands are relatively acceptable.

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