Edinburgh Napier University

  This study presents a miniaturised multiple input and multiple output /diversity antenna which is suitable for high data-rate communication systems such as mobile ultra-wideband (UWB). This antenna assembly comprises two identical planarinverted-F antennas, a T-shaped structure connecting them and afinite ground plane. The T-shaped structure improves theimpedance matching and suppresses the mutual coupling between the antenna elements over a wider bandwidth thanpreviously reported. The compact envelope dimension of this antenna is 50 × 90 × 7.5 mm3. Theoretical and experimentalS-parameters are illustrated for this antenna that fully cover the UWB operating frequency band of 3.1–10.6 GHz, with areflection coefficient and mutual coupling better than−10 and−20 dB, respectively. Acceptable agreement is obtained betweencomputed and measured radiation patterns, gains, envelope correlation coefficient and channel capacity loss. The proposedantenna is an attractive candidate to provide pattern diversity and enhance channel capacity in a rich scattering environment.1 IntroductionConventional narrowband wireless technologies suffer fromthe limitations of signal fading, multi-path, low immunity tothe possibility of arbitrary interference and limitedbandwidth when they operate in dense multi-pathenvironments such as occuring in buildings and vehicles.Owing to these deficiencies, they are less suitable foradoption in high data-rate wireless applications such ashigh-speed internet access ( > 200 Mbps) andhigh-definition TV video/audio streams. To tackle thisproblem, ultra-wideband (UWB) communication systems[1] have been introduced to cater to the ever increasingappetite for high data-rate wireless applications. Thesesystems feature low maximum emitted power ( < 75 nW/MHz), high data-rate ( > 500 Mbps) over short ranges( < 10 m) and large channel capacity deriving from 7.5 GHzbandwidth over the 3.1 to 10.6 GHz frequency spectrum.However, because the UWB systems use low transmittedpower have restricted the application to short-distancecommunication or moderate data rates.Multiple input and multiple output (MIMO) systemsadopting more than one antenna on the transmitting andreceiving end of the system have confirmed their capabilityin the published literature to offer superior data-rate,multi-path fading resistance and co-channel interferencereduction [2,3]. Therefore the combination of both UWBand MIMO communication technologies is one of the mostpromising and cost-effective solutions for maximising thechannel capacity and delivering a data-rate exceeding 1Gbps, using a robust wireless link employed in an indoorenvironment [4]. To ensure the sustainability of thisUWB-MIMO technology, it is imperative for antennadesigners to continue seeking viable approaches for newcompact size-reduced MIMO/diversity antennas that exhibitlow mutual coupling between elements, while preservinggood impedance matching and radiation performance overthe UWB band. They must also keep abreast of theincreasing demand for miniaturisation in the latest portablemobile/handheld devices. Taking into consideration therequirement of small inter-element spacing whilemaintaining good impedance matching over ultra-widebandwidth, significant efforts infinding solutions to reducethe wideband mutual coupling between two or more closelyplaced UWB antennas have been described [5–19]. Thesecoupling suppression methods can, in general, be classifiedas antenna element position adjustment [5–9], ground planegeometry modification [10–14] and combinations of boththe techniques [15–19]. By implementing one of thesemethods, the mutual coupling because of the near-fieldinduction, and sharing of a common ground between twoantenna elements [20], can be ameliorated.In the case of optimising the element positions [5–9], thismethod reduces the mutual coupling through minimisingthe near-field coupling current between antenna elements.Work in [5] demonstrated that it was possible to place twoantenna elements side by side with an edge-to-edge spacingof about 0.5λ0for a low mutual coupling, of better thanwww.ietdl.org444IET Microw. Antennas Propag., 2013, Vol. 7, Iss. 6, pp. 444–451&The Institution of Engineering and Technology 2013doi:10.1049/iet-map.2012.0574