Compact triple-band metamaterial inspired monopole antennas

Here we present a comparison analysis on the single loop resonator (SLR) inspired triple-band monopole antennas. Two configurations with rectangular and circular shaped radiation patches are presented. Simultaneously, two feed techniques with coplanar waveguide and microstrip feeds are performed to drive the antennas. And the conventional planar monopole antennas without the SLRs are also analyzed comparatively. Numerical and experimental methods are performed to demonstrate and discuss the proposed designs. Owing to the breakthroughs of modern wireless communications, the developments of miniaturized and multi-band communication components have been the main barriers in such science and engineering areas. Antenna, one of the important component, has been excited wide research attentions in recent years for multi-band applications. Monopole antenna is one of the most attractive configuration because of the compact sizes, flexible designs, low fabrication costs, and well radiation characteristics. Some of the monopole antenna configurations are reported by properly designing various resonator configurations to reduce operating frequencies, improve radiation pattern, and at the same time reduce cross-polarization characteristics. However, most of these antennas have complex configurations [1-3]. On the other hand, metamaterial units can be widely used for designing novel antennas to improve most of the characteristics comparing with conventional antennas [4]. For the monopole antenna integrated with metamaterial unit, some novel configurations have been reported elsewhere [5,6]. Here we systematically analyze a group of compact triple-band planar monopole antennas by integrating with a single loop resonator (SLR) as part of the radiation patch. Figure 1 present the designed four kind of SLR inspired antennas with rectangular and circular shaped radiation patches, and with coplanar waveguide and microstrip feedings. The corresponding conventional single band antennas with same dimensional size are also shown in Fig. 1 (see insets). All of the antennas are optimized with HFSS and fabricated based on the optimization results and the substrates used here (0.8-mm Rogers Ro4003: dielectric constant εr = 3.55 and loss tangent tanδ = 0.0027). The simulated and measured return loss properties of the four proposed SLR inspired antennas and four corresponding conventional antennas are shown in Fig. 1. For the metamaterial inspired antennas, both the numerical and experimental results show three dips around 2.4, 3.8 and 4.9 GHz. On the other hand, the simulated and measured reflection results for the conventional monopole antenna show only one transmission dip located in the range of 3.8–5 GHz. It means that our proposed metamaterial inspired antennas can operate at very lower frequency with the same antenna size for the conventional antenna. Therefore the proposed antennas have a highly compact size property. We can also know that the triple-band operating properties can be flexibly achieved by using different patch configurations and feeding methods. It means that we can use any of the four antennas to integrate in the transmit/receive devices depended on the special space and arrangement requirements. Frequency (GHz) -30 -25 -20 -15 -10 -5 0 R e fl e c ti o n ( d B ) (a) -25 -20 -15 -10 -5 0 (b) R e fl e c ti o n ( d B ) 0 1 2 3 4 5 6 -50 -40 -30 -20 -10 0 (c) R e fl e c ti o n ( d B ) Frequency (GHz) 0 1 2 3 4 5 6 -40 -35 -30 -25 -20 -15 -10 -5 0 0 1 2 3 4 5 6 -25 -20 -15 -10 -5 0 1 2 3 4 5 6 -25 -20 -15 -10 -5 0 1 2 3 4 5 6 -25 -20 -15 -10 -5 0 0 1 2 3 4 5 6 -30 -25 -20 -15 -10 -5 0 (d) R e fl e c ti o n ( d B ) R e fl e c ti o n ( d B ) R e fl e c ti o n ( d B ) R e fl e c ti o n ( d B ) R e fl e c ti o n ( d B ) 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 0 Frequency (GHz) Frequency (GHz) Frequency (GHz) Frequency (GHz) Frequency (GHz)Frequency (GHz)(e)(f)(g)(h)SimulationsMeasurements Fig. 1 The designed antennas and the corresponding simulated and measured return loss properties.Then the simulated co-polarization and cross-polarization radiation pattern characteristics for the fourmetamaterial inspired antennas at three corresponding reflection dips are analyzed, which indicate that the fourantennas exhibit typical eight-like radiation patterns in the co-polarization E-plane, whereas in theco-polarization H-plane they possess nearly omnidirectional radiation patterns. 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