H. Rmili, J.M. Floc’h and A. Khaleghi A wideband double-sided printed dipole antenna is presented for Cand X-bands. The proposed structure consists of a microstrip-fed annular-ring dipole with a central disc dipole printed on the top side of a substrate, and a modified annular-ring dipole, a connecting strip line and the ground plane printed on the bottom side. The antenna gives a wide resonant bandwidth that extends from 5 to 12.8 GHz, with a fractional bandwidth of 87.6%. Experimental and simulation results are presented and discussed in detail.
Introduction: With the rapid progress in modern communication system technology, the requirements for broadening frequency bandwidth have increased for both commercial and military applications. Wideband antennas are desirable in personal communication systems, small satellite communication terminals, and other wireless applications. In particular, communication systems that operate in the C- and X-bands are normally designed using separate antennas for each band. Since it is becoming more and more important to use such systems in one setting, it is desirable to design a single antenna that operates in both frequency bands [1]. To comply with this requirement, compact high-performance broadband planar antennas are needed. Recently, various types of patch antennas have been studied to meet the increasing trend for wideband antennas, and several techniques for size reduction and bandwidth enhancement have been proposed [2, 3]. The most important broadbanding techniques for microstrip patch antennas [4–6] are use of thicker and=or high permittivity substrates, shaping the patch, use of aperture coupling, mounting reactive loading, and use of parasitic elements or coupled resonators. In particular, the double-sided printed dipole-antenna [4, 7], which permits the use of coupled or stacked resonators, is one efficient structure for bandwidth enhancement. This structure is simple and easily fabricated, with easy integration into solid-state devices. In addition, the use of annular-ring patches is also one of the effective shaping techniques to improve the impedance bandwidth of microstrip printed antennas [5, 6]. In this Letter, we combine these two techniques in order to design a novel wideband printed dipole antenna operating in C- and X-bands. The antenna was fabricated and characterised by determining the impedance matching characteristics, the impedance bandwidth, and the radiation patterns. The impedance matching and the impedance bandwidth can be tuned by adjusting different design parameters.
Antenna design: The proposed antenna was etched on CuClad substrate with h ¼ 0.8 mm and er ¼ 2.17. The design parameters of the optimised structure are summarised in the caption of Fig. 1. The dimensions of the antenna are 75 50 mm. On the top side of the substrate, an annular ring of inner radius R2 and an outer radius R3, with a central disc of radius R1 is printed. The annular-ring dipole (R2, R3) is fed by a strip line of width W1. The printed radiator on the bottom side of the substrate is obtained from a circular-ring, with an inner radius R4 and an outer radius R5, by adding a rectangular element of dimensions L1 W1 and by subtracting a thin vertical slot of width S as shown in Fig. 1. This radiator was connected through a microstrip line of width W2 to a rectangular ground plane of dimensions L W3. The antenna was modelled, using IE3D method of moment code, in order to realise a wideband antenna which operates in both C- and X-bands. The main optimised parameters design are the radius R1 of the central disc, radii R2 and R3 of the of the annular-ring printed on the top side of the substrate, and radii R4 and R5 of the modified annular-ring printed on the bottom side of the substrate. Fig. 2 shows the simulated return loss variation for different lengths of L1. From the simulated results in Fig. 2, we can remark that the lower resonant frequency can be tuned by varying the length L1 of the rectangular element. This lower frequency at around f1 ¼ 5 GHz shifts when we modify L1 from the optimised value 15 mm, and by maintaining a constant coupling distance S of 1 mm between the ground plane and the rectangular element (L1 W1). In fact this frequency shift with L1 is due to the modification of the resonating path, whereas the variation of the impedance matching at the lower frequency of the wide band, with L1, is due to the modification of the coupling condition between the exciting-rectangular element and the central disc. 0
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Design of wideband double-sided printed dipole antenna for C- and X-band applications
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Fig. 1 Printed dipole antenna Dimensions, mm: L ¼ 75, W ¼ 50, L1 ¼ 15, W1 ¼ 6, L2 ¼ 5, W2 ¼ 1, L3 ¼ 21.5, W3 ¼ 10, S ¼ 1, R1 ¼ 6, R2 ¼ 7, R3 ¼ 8.6, R4 ¼ 10, R5 ¼ 12
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Results: The optimised printed dipole antenna prototype was fabricated based on the dimensions specified in the caption of Fig. 1. The return loss of the structure was measured over the frequency range 4– 14 GHz using a Wiltron 360 B vector network analyser. Measurements on the radiation patterns were performed in an anechoic chamber. Fig. 3 shows both measured and simulated results of the return loss S11. As shown, relatively good agreement between simulated and measured return loss was observed. The discrepancies between simulated and measured might be attributed to the effect of the SMA connector and fabrication imperfections. The realised antenna presents a wide resonant band that extends from 5 to 12.8 GHz, with an impedance matching bandwidth of approximately 87.6 % (for S11 < 10 dB). As a result, it can be seen that the impedance bandwidth of this resonant band is suitable for communication systems operating in the C- and X-bands. The measured far-field radiation patterns in the x-z and y-z planes, at the resonance frequencies 5.56, 7.72, 9.34 GHz, are shown in Fig. 4. The radiation patterns present a certain degree of similarity in both x-z and y-z planes. These radiation patterns exhibit the typical nulls on the dipole axis (x-axis), at y angles around 0 and 180 . Moreover, some patterns (especially for f ¼ 5.56 and 9.34 GHz) present a notable degree of symmetry around the direction y ¼ 0, in both planes. We note that the radiation is directed towards both negative and positive y-axis. This effect is explained by the radiated fields of the radiators printed on both sides of the substrate. The measured peak gains observed in the range 5–12.8 GHz at the frequencies 6.68, 8.88, 9.56, 10.61 GHz are 3, 4.1, 2.9, 3.5 dBi, respectively.
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Conclusions: A novel wideband printed dipole antenna for multiple wireless services has been realised. The proposed double-sided printed dipole antenna exhibits a wideband impedance matching. The resonant bandwidth is 7.8 GHz (5–12.8 GHz). The wide impedance bandwidth, the relatively good gain and radiation characteristics, and the simple feeding of the proposed antenna make it a good choice for communication systems that operate in both C- and X-bands. The antenna could be useful, for example, as a radiating element in a sector zone base station antenna. # The Institution of Engineering and Technology 2006 21 June 2006 Electronics Letters online no: 20061948 doi: 10.1049/el:20061948 H. Rmili, J.M. Floc’h and A. Khaleghi (IETR, INSA, 20 avenue Buttes des Coe¨ smes, 35043 Rennes, France) E-mail:
[email protected] References 1 Eldek, A.A., Elsherbeni, A.Z., and Smith, C.E.: ‘Wide-band modified printed bow-tie antenna with single and dual polarization for C- and X-band applications’, IEEE Trans. Antennas Propag., 2005, 53, (9), pp. 3067–3072 2 Shackelfford, A.K., Lee, K.F., and Luk, K.M.: ‘Design of small-size wide-bandwidth microstrip-patch antennas’, IEEE Antennas Propag. Mag., 2003, 45, (2), pp. 75–83 3 Hori, T.: ‘Broadband=multiband printed antennas’, IEICE Trans. Commun., 2005, E88-B, (5), pp. 1809–1817 4 Su, C.W., Liu, Y.T., Chen, W.S., Cheng, Y.T., and Wong, K.L.: ‘Broadband circularly polarized printed-spiral-strip antenna for 5-GHz WLAN operation’, Microwave Opt. Technol. Lett., 2004, 41, (5), pp. 163–165 5 Liu, J.C., Zeng, B.H., Wu, C.Y., and Chang, D.C.: ‘Double-ring slot antenna with tree-shaped coupling strip for WLAN 2.4=5-GHz dual-band applications’, Micro. Opt. Technol. Lett., 2005, 47, (11), pp. 374–379 6 Liang, J., Chiau, C.C., Chen, X., and Parini, C.G.: ‘Printed circular ring monopole antennas’, Microw. Opt. Technol. Lett., 2005, 45, (6), pp. 372– 375 7 Ma, T.G., and Jeng, S.K.: ‘A printed dipole antenna tapered slot feed for ultrawide-band applications’, IEEE Trans. Antennas. Propag., 2005, 53, (11), pp. 3833–3836
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Fig. 4 Measured x-z plane and y-z plane radiation patterns at resonant frequencies 5.56, 7.72, 9.34 GHz
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