The design and analysis of meta-material inspired loaded monopole antenna for multiband operation are reported. The proposed antenna consists of multi resonators inspired from half mode composite right/left handed cells, which has a simple structure, compact size, and provides multiband functionalities. As a proof of concept, a triple band antenna covering all possible WiMAX operating bands, has been designed, fabricated, and characterized. The hosting monopole patch itself generates resonance for 3.3–3.8 GHz band, whereas the loaded metamaterial cells add extra resonance frequencies. The loading of two resonator cells introduces two extra resonances for 2.5–2.7 GHz and 5.3–5.9 GHz bands, respectively. The antenna's operating principle and design procedures with the aid of electromagnetic full wave simulation and experimental measurements are presented. The antenna has good omnidirectional patterns at all three bands. The monopole patch size is 13.5 × 6.5 mm2 and the whole antenna size (including the feed line) is 35 × 32 mm2. Compared with conventional single band microstrip patch radiator, the radiator size of this antenna is only 8.5% at 2.5 GHz, 17% at 3.5 GHz, and 37% at 5.5 GHz.

A super-wideband (SWB) omnidirectional antenna is reported in Lau et al. in 2005 and 2008, but the antenna structure was complex and the radiation properties were unsatisfactory. In this paper, a SWB omnidirectional antenna with simple structure and improved radiation properties is presented. The antenna just consists of a two-stage inverted cone and two shorting pins. The proposed two-stage cone can improve the impedance matching in super-wide bandwidth, and the optimized shorting pins can reduce the cut-off frequency more than 50%. The calculated and measured results are investigated to confirm the antenna performances. The impedance bandwidth of the antenna for voltage standing wave ratio ≤ 2 achieves more than 1:22.1, covering 0.905 GHz to the above band. The smaller sizes than those referred by Lau et al. in 2008 are obtained. The profile of the antenna is 0.078λc, and the diameter of the radiation body is 0.217λc (λc is the wavelength of the cut-off frequency of the antenna). In addition, the radiation properties of the kind of SWB omnidirectional antenna are improved obviously. In the whole band, the ripple levels in horizontal radiation patterns are not more than 6.6 dB, and the cross-polarized levels are reduced by 9 dB.

In this paper, triple-band stacked microstrip patch antennas (MPAs) are presented with wide impedance bandwidth and suppressed cross-polarization level. Triangular and circular shaped slots are embedded in the patch of antenna. Slot-loaded microstrip patches are fed with meandered microstrip line supported by a semi-ground plane structure. Triangular shaped slot-loaded MPA shows triple resonance at frequencies 2.2, 4.45, and 5.3 GHz having bandwidth of 45.9, 19.23, and 15.67%, respectively. Circular shaped slot-loaded MPA also shows triple resonance at frequencies 2.2, 4.42, and 5.38 GHz having bandwidth of 50.24, 33.21, and 13.43%, respectively. Using circular slot in place of triangular; bandwidth of the first and the second band is improved by 4.34 and 13.98%, respectively. Both the proposed antennas show an omnidirectional radiation pattern at all three resonance frequencies in the xz-plane with almost 0 dBi gain. Both the proposed antennas are fabricated on a FR-4 epoxy substrate and show a minimum level of cross-polarization radiations.