6 A very compact radiator using a ZOR split ring resonator (SRR) is proposed and adopted for miniature symmetric MIMO antennas by S. The radiators are connected in the LC-based branch coupler for lower coupling, 5 but 3D folded monopoles share a shorted loop for better decoupling. Simple meandered quarter-wave long radiators are separated by a split ground and a hybrid coupler by Sharawi et al., 4 and Bhatti et al., 5 respectively. Although isolation is greater than 12 dB, the structure uses a microstrip fed monopole-type decoupling element occupying a large volume. Wang, et al., 3 demonstrated two microstrip fed antennas having the layered and vertical parts of the radiators perpendicular to the layered ground by periodically meandering a decoupling element for better isolation. Payandehjoo et al., 2 utilized an electromagnetic band gap (EBG) structure to increase diversity gain by weakening the coupling between two antennas however, the structure is large and the frequency is outside the WiMAX band. The radiation patterns and isolation are acceptable, but the structure is physically large, occupying the top edge and two sides of the handset device. A number of MIMO antennas were prototyped by Mak et al., 1 with a feature of trapping the undesirable interaction between one element and the other, imitating a closed current loop suppressing a long current flow.
This challenges antenna designers to increase isolation between multiple antennas while reducing antenna size. Multi input, multi output (MIMO) antennas must provide higher quality mobile communication through diversity in RF signal transmission and reception. The design is validated with a full-wave simulation that is in good agreement with measurements of the fabricated prototype, which uses a low cost FR4 process versus ceramic-based chips or LTCC.įigure 1 Geometry of the radiating element attached to the ground top overall view (a), 3D view of the radiating element (b), side-view showing the thin layers (c). The two radiating elements are separated by just 10 mm and a folded line between them is optimized to obtain isolation above 10 dB over the 250 MHz bandwidth.
The radiator is used in the design of two antennas on the top-edge of a MIMO handset with a total length equal to 0.108 λ g(much less than a quarter-wavelength). A compact bandwidth-broadened and isolation-improved MIMO antenna appropriate for LTE communication employs a small 0.034 λ glong radiator designed to have an in-phase and dense electric field flux at the zeroth order resonance (ZOR) of 2.5 GHz for circumventing the problem of degraded antenna gain and four thin FR4 layers to create closely located resonances for expanding the bandwidth.
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