G.K. Pandey, H.S. Singh, P.K. Bharti and M.K. Meshram A metamaterial-based novel compact microstrip antenna is presented for ultra-wideband (UWB) applications. The antenna consists of two layers of metamaterials made by etching a π-shaped slot and crossed-shaped slots, on the radiating patch and the ground plane, respectively. The series capacitance and shunt inductance developed due to the patterned radiating patch and ground plane lead to the left-handed behaviour of the metamaterial. The proposed antenna has a compact size of 30.8 × 27.6 × 0.8 mm3 and is fed by a 50 Ω microstrip line. The impedance bandwidth (−10 dB) is from 3 GHz to more than 14 GHz with maximum radiation in the horizontal plane and tends towards a directional pattern as the frequency increases.
Introduction: Ultra-wideband (UWB) systems have attracted significant research attention since the Federal Communication Commission (FCC) released a band of 7.5 GHz (3.1–10.6 GHz) as UWB in 2002 [1]. UWB systems have the advantages of low complexity, low power consumption, capability of high data rate, low interference, good time-domain resolution and are resistant to severe multipaths. Microstrip patch antennas, because of their advantages of low profile, a conformal structure and easy integration with microwave circuit components, can be a very good candidate for UWB systems. The major limitation of the microstrip antenna is its narrow impedance bandwidth which limits its application to UWB systems. Techniques like increasing the height of the substrate, the use of a low permittivity substrate, loading the patch with slots [2], stacking different antenna elements [3], the use of a parasitic element and the use of electromagnetic band gap structures [4] have been proposed to mitigate the narrow bandwidth problem. Recently, some metamaterialbased microstrip patch antennas have been reported [5–7] with wide impedance bandwidth, but the complete FCC’s defined UWB is not covered by them and they are fabricated on high-cost substrates generally not used in low-cost system design. 27.6
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high-frequency structure simulator [8] and the computer simulation technology (CST) Microwave Studio (MWS) [9] to validate the proposed antenna. Antenna design and configurations: The geometry of the proposed antenna along with the fabricated prototype and detailed dimensions are shown in Fig. 1. The antenna is fabricated on a 0.8 mm-thick FR4 substrate (εr = 4.4) of size 30.8 × 27.6 mm2. The radiating patch consists of metamaterial unit cells made up of π-shaped slots while the ground plane consists of crossed-shaped slots for the metamaterial structure. The patterned radiating patch and ground plane are coupled to form a capacitive–inductive equivalent circuit which can induce a backward wave that travels along the plane of the patch and induce radiation more in the plane of the antenna [5]. Since the antenna is fed by a 50 Ω microstrip line, the metamaterial pattern is not created under the line for transmission consistency. Initially, the unit cells of the radiating patch were arranged to form a rectangular patch which provides wide impedance matching but the FCC’s defined UWB is not covered (antenna 1). Furthermore, to cover the whole UWB, a unit cell is removed from the rectangular lattice of the patch near the feed. Owing to this defect, the whole UWB is covered with the reduction of lower edge operating frequency, as shown in Fig. 2. reflection coefficient, dB
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Results and discussion: The proposed antenna was optimised, then fabricated by the T-Tech QC-5000 micro-milling machine. The reflection coefficient was measured by an Agilent E8364B vector network analyser. The variation of reflection coefficient with frequency is shown in Fig. 3. It is observed that the antenna shows a −10 dB impedance bandwidth from 3 GHz to more than 14 GHz (more than 129% bandwidth) which covers the whole of the FCC’s defined UWB. The measured result shows some deviation from the simulated results; this may be due to fabrication imperfection or because measurement is carried out in the scattering environment.
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Fig. 1 Proposed metamaterial-based UWB antenna a Geometry of proposed antenna (dimensions: millimetres) b Unit cell of proposed antenna (dimensions: millimetres) c Fabricated prototype of antenna
In this Letter, a novel compact low-cost metamaterial-based patch antenna is proposed for UWB applications. The proposed antenna consists of novel metamaterial unit cells in the radiating patch and ground plane; furthermore, a defect is created near the feed by removing a unit cell from the regular lattice of the radiating patch and ground plane which helps to improve the impedance matching. Owing to the use of metamaterial structures, the maximum radiation takes place along the horizontal direction as the frequency increases, instead of in the vertical direction as in the case of a simple microstrip patch antenna. Good agreement is found between the simulated and measured results. The simulations were carried out using both Ansoft’s
The measured radiation patterns in the xy-, yz- and zx-planes at different frequencies (4, 8 and 12 GHz) are shown in Fig. 4. At the lowerfrequency side (4 GHz), the radiation pattern is like a monopole antenna pattern. Although at the higher-frequency side, owing to the left-handed transmission characteristics of metamaterial maximum radiation is dominant in the antenna plane (xy-plane) and maximum radiation is nearly along the x-direction. At higher frequencies, the radiation is due to the higher-order modes which are responsible for splitting of the radiation lobe. The peak realised gain and computed total radiation efficiency variation with frequency are shown in Fig. 5. It is observed that the total radiation efficiency lies in the range of 94% (3.5 GHz) to 54% (14 GHz). As the frequency increases, the losses related to substrate increase, which results in reduced radiation efficiency; therefore, if the substrate with low losses are considered the efficiency can be improved.
ELECTRONICS LETTERS 28th August 2014 Vol. 50 No. 18 pp. 1266–1268
The realised gain lies in the range of 1.5 dBi (3 GHz) to a maximum value of 7.2 dBi (13 GHz), which shows that the antenna tends to directional radiation characteristics as the frequency increases. 0
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© The Institution of Engineering and Technology 2014 28 June 2014 doi: 10.1049/el.2014.2366 One or more of the Figures in this Letter are available in colour online. G.K. Pandey, H.S. Singh, P.K. Bharti and M.K. Meshram (Department of Electronics Engineering, IIT(BHU), Varanasi 221 005, India) E-mail:
[email protected]
frequency, GHz
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Conclusion: A printed compact metamaterial-based antenna is proposed for UWB applications. The proposed antenna consists of a radiating patch and the ground plane patterned as a metamaterial structure. The antenna shows a wide impedance bandwidth (−10 dB) from 3 GHz to more than 14 GHz (more than 129%). The radiation characteristics of the antenna show maximum radiation in the antenna plane and tend towards a directional radiation pattern as the frequency increases which results in a high-gain antenna at the higher-frequency side. The antenna has good pulse handling capability for UWB applications. The proposed antenna can be a potential candidate for UWB applications with its unique radiation characteristics as compared to the conventional UWB antennas. Acknowledgment: G.K. Pandey thanks the University Grant Commission (UGC), New Delhi, India for providing financial support in terms of a senior research fellowship (SRF).
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antennas (transmitter and receiver) were placed in the far-field region (face-to-face, side-by-side y-direction and side-by-side x-direction). The transmitter is excited by a Gaussian signal (3.1–10.6 GHz) that complies with the FCC indoor and outdoor power spectrum mask. The transmitted and received signals are shown in Fig. 6. The fidelity factors in the case of face-to-face, side-by-side y-direction and side-by-side x-direction are obtained as 84, 88 and 71%, respectively. The time-domain analysis shows that the antenna has good pulse handling capability in the UWB frequency band.
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Furthermore, to measure the pulse handling capability of the proposed UWB antenna, time-domain analysis was carried out along with fidelity factor calculation [10] using CST MWS. For such purpose, two
References 1 Federal Communication Commission: ‘First order and report: revision of part 15 of the Commission’s rules regarding UWB transmission systems’, April 2002 2 Chen, W.L., Wang, G.M., and Zhang, C.X.: ‘Bandwidth enhancement of a microstrip-line-fed printed wide-slot antenna with a fractal-shaped slot’, IEEE Trans. Antennas Propag., 2009, 57, (7), pp. 2176–2179 3 Matin, M.A., Sharif, B.S., and Tsimenidis, C.C.: ‘Probe fed stacked patch antenna for wideband applications’, IEEE Trans. Antennas Propag., 2007, 55, (8), pp. 2385–2388 4 Yousefi, L., Iravani, B.M., and Ramahi, O.M.: ‘Enhanced bandwidth artificial magnetic ground plane for low-profile antennas’, IEEE Antennas Wirel. Propag. Lett., 2007, 6, (10), pp. 289–292 5 Li, L.W., Li, Y.N., Yeo, T.S., Mosig, J.R., and Martin, O.J.F.: ‘A broadband and high-gain metamaterial microstrip antenna’, Appl. Phys. Lett., 2010, 96, 164101, pp. 1–3 6 Han, X., Song, H.J., Yi, Z.Q., and Lin, J.D.: ‘Compact ultra-wideband microstrip antenna with metamaterials’, Chin. Phys. Lett., 2012, 29, (11), 114102, pp. 1–3 7 Xiong, H., Hong, J.S., and Peng, Y.H.: ‘Impedance bandwidth and gain improvement for microstrip antenna using metamaterials’, Radio Eng., 2012, 21, (4), pp. 993–998 8 Ansoft High Frequency structure Simulator (HFSS), [Online]. Available at http://www.ansoft.com 9 Computer simulation technology microwave studio (CST MWS), [Online]. Available at http://www.cst.com 10 Koohestani, M., Pires, N., Skrivervik, A.K., and Moreira, A.A.: ‘Time-domain performance of patch-loaded band-reject UWB antenna’, Electron. Lett., 2013, 49, (6), pp. 385–386
ELECTRONICS LETTERS 28th August 2014 Vol. 50 No. 18 pp. 1266–1268
