M. Gopikrishna, D.D. Krishna, C.K. Aanandan, P. Mohanan and K. Vasudevan A novel ultra-wideband (UWB) antenna consisting of a linear tapered slot in the ground plane and a microstrip to slotline transition is investigated. The antenna possesses a wide bandwidth from 2.95 – 14 GHz for jS11j , 210 dB and shows stable radiation patterns with an average gain of 3 dBi throughout the band. Measured group delay and transmission characteristics indicate that the antenna has good pulse handling capabilities.
Introduction: Tapered slot antennas (TSAs) have attracted commercial and military interests owing to their multi-octave impedance bandwidth, simple design and conformability with MMIC. With the rise of wireless networking they are used in portable products for WLAN and in millimetre-wave imaging systems due to symmetrical patterns and high, constant gain throughout the band. By adjusting the taper length and angle, radiation from a TSA can be designed as broad, bore sight or directional [1]. The taper parameters have little effect on the overall matching and, typically, quarter-wave stub terminated or open microstrips [2– 4], or baluns [5] are incorporated in the antenna to improve matching. The complex matching procedures employed would not only consume PCB space but also result in multi-reflecting waves in the antenna, thereby widening the transmitted signal. Because of this, implementation of these antennas are more popular in areas such as ground penetrating radar and imaging systems than in portable communication devices. Compact UWB antenna designs [6, 7] are of great demand in emerging applications such as WiMedia, which are realised in constricted space in the PCB. In this Letter, we propose a compact slot antenna for UWB radios. The design comprises a linear tapered slot in the ground plane that is excited using a microstrip line. Instead of using the complex matching procedures discussed above, a rectangular cut is optimised in the 50 V feed line to match multiple resonances in the antenna, resulting in wide impedance bandwidth covering the 3.1– 10.6 GHz UWB. The antenna provides omnidirectional coverage with appreciable gain throughout the band. Reasonably good group delay and the transmission characteristics further confirm its suitability for portable UWB devices.
y-direction. To get an insight into the phase linearity of the transmitted signals in the far field, group delay measurements were performed using two identical prototypes of the antenna. As indicated in Fig. 5, the delay remains constant throughout the band with variation less than a nanosecond for both orientations tested. Furthermore, the transmission characteristics of the antenna are fairly flat for these orientations. These indicate superior pulse handling capabilities as demanded by modern communication systems.
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Antenna design: Fig. 1 shows the geometry of the antenna printed on an FR4 substrate with permittivity 1r ¼ 4.4 and thickness of 1.6 mm. A linear tapered slot in the ground plane is excited using a microstrip. A rectangular cut in the microstrip feed improves the impedance match. The proposed simple slot antenna design has a compact profile of L W ¼ 30 13.5 mm2, which is much smaller than that reported in [2–5].
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Experimental results and discussion: Return loss measurements of the antenna performed using an R&S ZVB 20 vector network analyser indicate a wide bandwidth from 2.95– 14 GHz. This shows close correspondence with the simulation in HFSS as in Fig. 2. The measured radiation pattern of the antenna is shown in Fig. 3 for different frequencies. These are omnidirectional in the H-plane (x-z plane) and bidirectional in the E-planes (x-y and y-z). The peak gain of the antenna remains constant throughout the band, as shown in Fig. 4, with polarisation in the
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ELECTRONICS LETTERS 25th September 2008 Vol. 44 No. 20
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Conclusion: The design of a linear tapered antenna operating in the FCC 3.2– 10.6 GHz band is proposed. The design is simple and compact since there are very few design parameters. The measured electrical parameters of the antenna as well as its radiation patterns are excellent with good pulse handling capabilities. For these reasons, the present design stands out as a potential candidate for portable UWB radios.
1 Matsui, A., Kanda, Y., and Takekoshi, S.: ‘Linearly tapered slot antenna element by experimental approach’. EMTS 2007 Int. URSI Commission B – Electromagnetic Theory Symp., Ottawa, ON, Canada, July 2007 2 Yoon, I.J., Kim, H., Chang, K., Yoon, Y.J., and Kim, Y.H.: ‘Ultra wideband tapered slot antenna with band-cut off characteristic’, Electron. Lett., 2005, 41, (11), pp. 629– 630 3 Ma, T.G., and Jeng, S.K.: ‘A printed dipole antenna with tapered slot feed for ultrawide-band applications’, IEEE Trans. Antennas Propag., 2005, 53, (11), pp. 3833–3836 4 Verbiest, J.R., and Vandenbosch, G.A.E.: ‘Low-cost small-size tapered slot antenna for lower band UWB applications’, Electron. Lett., 2006, 42, (12), pp. 670– 671 5 Kwon, D.H., Balzovsky, E.V., Buyanov, Y.I., Kim, Y., and Koshelev, V.I.: ‘Small printed combined electric-magnetic type ultra wideband antenna with directive radiation characteristics’, IEEE Trans. Antennas Propag., 2008, 56, (1), pp. 237–241 6 Su, S.W., Chou, J.H., and Wong, K.L.: ‘Internal ultrawideband monopole antenna for wireless USB dongle applications’, IEEE Trans. Antennas Propag., 2007, 55, (4), pp. 1180– 1183 7 Bahadori, K., and Samii, Y.R.: ‘A miniaturized elliptic-card UWB antenna with WLAN band rejection for wireless communications’, IEEE Trans. Antennas Propag., 2007, 55, (11), pp. 3326– 3332
Acknowledgments: M. Gopikrishna and D. D. Krishna acknowledge the University Grants Commission and the Department of Science and Technology, respectively, for financial assistance for this work. The measurements were carried out using the facilities created under the DST-FIST programme. # The Institution of Engineering and Technology 2008 4 August 2008 Electronics Letters online no: 20082269 doi: 10.1049/el:20082269 M. Gopikrishna, D.D. Krishna, C.K. Aanandan, P. Mohanan and K. Vasudevan (Centre for Research in Electromagnetics and Antennas, Department of Electronics, Cochin University of Science & Technology, Cochin 682022, India) E-mail:
[email protected]
ELECTRONICS LETTERS 25th September 2008 Vol. 44 No. 20
