Ground modified double-sided printedcompact UWB antenna

R. Azim, M.T. Islam and N. Misran

A double-sided printed compact antenna for UWB application isproposed. The proposed antenna, having a total size of 30 × 22 mm,consists of a patch fed by a microstrip line and a partial groundplane. The modified ground plane with triangular shaped slots on itstop edge helps to increase the bandwidth of the proposed antenna.The double-sided printed antenna has a bandwidth (VSWR ≤ 2)from 3.08 to 15.90 GHz and a maximum gain of 5.9 dBi. Antennaradiation patterns show stable variation within its operating band.

Introduction: Owing to its high data transmission rate, large bandwidth,and short-range characteristics, ultra-wideband (UWB) technology hasbeen widely used in various applications such as the wireless personalarea network (WPAN), wireless body area network (WBAN), indoorlocalisation and biomedical imaging [1]. Designing UWB antennas tomatch these applications is still a major challenge and has attractedthe interest of many researchers [2, 3]. Despite UWB performance,the antennas proposed in [2] and [3] are not suitable to integrate intoprinted circuit boards owing to their large size and the manufacturingdifficulties.

Owing to its low cost, low profile, ease of fabrication and wide band-width, the printed planar structure appears to be the most promising can-didate for wideband applications. Recently, various planar antennashave been proposed and investigated because of their advantages[4–7]. For example, a small UWB elliptical ring antenna fed by a copla-nar waveguide has been proposed and investigated in [8]. It achievedwideband performance by extending the length of the elliptical ring’smajor axis and demonstrated an ultra-wide 10 dB return loss bandwidthfrom 4.6 to 10.3 GHz. Although the antenna has fairly compactdimensions of 29 × 26 mm, it does not cover the entire ultra-wideband.An improved design of a planar elliptical dipole antenna for UWBapplications has also been developed recently [9]. By using ellipticalslots on the dipole arms, the antenna has achieved wideband character-istics, having an operating bandwidth of 94.4%. However, the antennadoes not process a physically compact profile, having dimensions of106 × 85 mm.

In this Letter, a new double-sided printed antenna with compact sizeand good impedance characteristics is presented for UWB applications.To enhance the impedance bandwidth, antenna parameters are optimisedand the ground plane is modified by cutting slots on the top edge to forma symmetrical sawtooth shape. By modifying the ground plane a widerimpedance bandwidth has been achieved compared to the design in[4–9]. The designed antenna was successfully implemented andexperimental results are presented.

y

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units: mm

initial design

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triangular shape slot

√5

4

√5 1

top view bottom view

a

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Fig. 1 Geometry of proposed antenna and photograph of prototype

a Geometry of proposed antennab Photograph of prototype

Antenna configuration: The configuration of the initial design of theproposed antenna is shown in Fig. 1a. The radiating patch, which has

ELECTRONICS LETTERS 6th January 2011 Vol. 47

a compact size of 14.5 × 14.75 mm is printed on the top side of anFR4 PCB substrate of thickness 1.6 mm and relative permittivity 4.6.A microstrip line of width 3 mm is printed on the same side of thepatch on the substrate as the radiator. The finite partial ground planewith initial dimensions of 30 × 7.5 mm is printed on the bottom sideof the substrate. The length of microstrip line is fixed at 7.25 mm toachieve 50 V characteristic impedance. An SMA connector is connectedto the port of the microstrip feed line. There is an overlap of 0.25 mmbetween the patch and the ground plane. The geometric parameters ofthe proposed antenna structure can be adjusted to tune the VSWR aswell as the bandwidth over a wide range of frequencies. From the optim-isation of antenna parameters it is found that the antenna is capable oftuning from 3.04 to 11.94 GHz providing an impedance bandwidth of8.9 GHz.

To improve the bandwidth of the proposed antenna, the ground planeis modified by cutting triangular shaped slots on its top edge. The res-ultant ground plane with a symmetrical sawtooth shaped edge isshown in Fig. 1a. Fig. 1a also shows the geometry of a single triangularshaped slot. Fig. 2a shows that the antenna with the modified groundplane having optimised triangular shaped slots with dimensions of4 mm × p

5 mm × p5 mm can be operated from 2.9 to 16.0 GHz pro-

viding a bandwidth of 13.1 GHz. Compared to the antenna having noslots in the ground plane, the antenna with triangular shaped slots onthe top edge of the ground plane can enhance the bandwidth by 45%(4.1 GHz). The insertion of slots on the top edge of the ground planeincreases the gap between the radiating patch and the ground plane,resulting in enhancement of impedance bandwidth.

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2 4 6 8 10 12 14 16frequency, GHz

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measured

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, dB

i

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Fig. 2 Simulated and measured VSWR for proposed antenna and measuredmaximum antenna gain

a Simulated and measured VSWRb Measured maximum antenna gain

Results and discussion: The proposed antenna has been analysed andoptimised by Zeland IE3D simulation software based on the methodof moments. The antenna prototype was fabricated as shown inFig. 1b. The antenna was measured in an anechoic chamber using anAgilent E8362C vector network analyser and the Satimo hybridStarLab 16 near-field antenna measurement system. It is observedfrom Fig. 2a that the measured impedance bandwidth (VSWR ≤ 2) ofthe proposed antenna is from 3.08 to 15.9 GHz, which is equivalentto 135%. The measured results are in good agreement with those ofthe simulation. The difference between simulation and measurement ismostly due to the influence of the feeding cable and inaccuracies in fab-ricating the antenna structure. Despite its very small size, the proposedantenna has achieved wider bandwidth than the antennas proposed in[4–9] and is able to tune over a wide bandwidth to cover the entirerange of 3.1 to 10.6 GHz assigned for UWB applications. Fig. 2b illus-trates the measured gain of the fabricated antenna in the frequency rangeof 3 to 11 GHz. With an average gain of 4.04 dBi, the antenna achieves amaximum gain of 5.9 dBi at 9.4 GHz and the measured gain variation isless than 2 dBi. It is obvious that the measured gain is higher than thegain of those antennas reported earlier in [5] and [6]. The radiationcharacteristics of the frequencies across the band have been studied.Fig. 3 shows the measured radiation patterns of the xz-plane and the

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yz-plane at 3.6, 7.2 and 9.6 GHz. For brevity, only the copolarisationfield is shown here. It can be observed that the yz-plane radiation patternsare almost omnidirectional and the xz-plane patterns are monopole-like.Although some dips observed in both the xz- and the yz-plane could bedue to the fact that the microstrip feed line is directly printed below theslotted partial ground plane, the radiation patterns through out the oper-ating band are quite stable.

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0270

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3.6 GHz 7.2 GHz 9.6 GHz

a b

Fig. 3 Measured radiation patterns

a xz-planeb yz-plane

Conclusion: A printed compact antenna has been proposed and fabri-cated. The antenna having a total size of 30 × 22 mm is printed onboth sides of a low-cost FR4 PCB substrate. The modified groundplane with triangular shaped slots on the top edge helps to increasethe impedance bandwidth. It is observed from measurement that theproposed antenna with the modified finite ground plane has achievedan impedance bandwidth (VSWR ≤ 2) of 12.82 GHz (3.08 to15.90 GHz), which covers the entire UWB band. The symmetric andstable radiation pattern with an average gain of 4.04 dBi makes theproposed antenna suitable for use in UWB applications.

ELECTRON

# The Institution of Engineering and Technology 201112 November 2010doi: 10.1049/el.2010.3160One or more of the Figures in this Letter are available in colour online.

R. Azim, M.T. Islam and N. Misran (Institute of Space Science(ANGKASA) and Department of Electrical, Electronic and SystemsEngineering, Universiti Kebangsaan Malaysia, 43600 UKM Bangi,Selangor, Malaysia)

E-mail: titareq@yahoo.com

References

1 Verbiest, J.R., and Vandenbosch, G.A.E.: ‘A novel small-size printedtapered monopole antenna for UWB WBAN’, IEEE Antennas Wirel.Propag. Lett., 2006, 5, (1), pp. 377–379

2 See, T.S.P., and Chen, Z.N.: ‘An electromagnetically coupled UWB plateantenna’, IEEE Trans. Antennas Propag., 2008, 56, (5), pp. 1476–1479

3 Zhou, H., Liu, Q., Sun, B., and Yang, Y.: ‘A band-notched swallow-tailed planar monopole antenna for UWB application’, Microw. Opt.Technol. Lett., 2008, 50, (3), pp. 793–795

4 Kiminami, K., Hirata, A., and Shiozawa, T.: ‘Double-sided printed bow-tie antenna for UWB communications’, IEEE Antennas Wirel. Propag.Lett., 2004, 3, pp. 152–153

5 Ren, Y.J., and Chang, K.: ‘An annual ring antenna for UWBcommunications’, IEEE Antennas Wirel. Propag. Lett., 2006, 5, (1),pp. 274–276

6 Xiao, J.X., Wang, M.F., and Li, G.J.: ‘A ring monopole antenna forUWB application’, Microw. Opt. Technol. Lett., 2010, 52, (1),pp. 179–182

7 Liu, J., Gong, S., Xu, Y., Zhang, X., Feng, C., and Qi, N.: ‘Compactprinted ultra-wideband monopole antenna with dual band-notchedcharacteristics’, Electron. Lett., 2008, 44, (12), pp. 710–711

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9 Nazli, H., Bicak, E., Turetken, B., and Sezgin, M.: ‘An improved designof planar elliptical dipole antenna for UWB applications’, IEEE AntennasWirel. Propag. Lett., 2010, 9, pp. 264–267

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