We propose a miniaturized design of a four-element dual-band multiple-input multiple-output antenna system. The dual-band function is obtained by etching an “L” slot in the radiating patch. The edge-to-edge elements spacing is only 0.023${\boldsymbol {\lambda_{0}}}$. A decoupling structure consisting of cross-shaped metal strips shorted to the ground plane using vias is first introduced. Then, metalized walls are used to enhance the isolation level by realizing the pattern diversity. The measured resonant frequencies are centered at 3.5GHz and 5.7GHz with bandwidths of 58MHz and 43MHz, peak gains of 2.7dBi and 2.85dBi, peak efficiencies of 63% and 65%, respectively. A considerable measured mutual coupling reduction of 10.8dB in the lower band and 15.6dB in the upper band is realized. The overall size of the design is 0.41${\boldsymbol {\lambda_{0}}}$ x 0.41${\boldsymbol {\lambda_{0}}}$ x 0.04${\boldsymbol {\lambda_{0}}}$ with minimum isolation levels of 18.4dB and 22.7dB in the lower and upper bands, respectively. The envelope correlation coefficient is lower than 0.08 across both operating bandwidths. The measured results validate the good diversity performance of the MIMO system.

A two-port structure-shared planar ultra-wideband antenna with high isolation is presented in this paper. The proposed antenna consists of a planar monopole and two back-to-back tapered slots etched on the monopole. The monopole and the tapered slots are fed by microstrip line and differential feeding network, respectively. The differential feeding network of the tapered slots excites modes which are orthogonal to those of the monopole. Therefore, high isolation between the two ports can be achieved without additional decoupling structures. The measured results show that the proposed antenna can operate from 3 to 10 GHz with reflection coefficient of the two ports lower than -10 dB and isolation higher than 38 dB. The measured realized peak gains are above 2.6 dB and the measured envelope correlation coefficients are less than 9×10-5. The proposed UWB MIMO antenna can be applied in the MIMO communication systems, especially those requiring high isolation.

This paper presents a low-profile coplanar du-al-polarized dual-band base station antenna array. A slotted patch antenna operating from 0.82 to 0.99 GHz with four shorting strips is proposed and analyzed. The four shorting strips are employed not only to improve the impedance matching in the lower band, but also to remove the center part of the patch, thus making room for higher band dipoles operating from 1.68 to 2.86 GHz. The height of the proposed array is nearly half of the conventional base station array while other performances are guaranteed. Measured results show that the proposed antenna array has wide impedance bandwidths of 18.7% (0.82 ~ 0.99 GHz) and 57.9% (1.68 ~ 2.86 GHz) (VSWR 24.6 dB) and high isolations (> 30 dB and > 25 dB in lower and upper bands, respectively) are achieved. The proposed antenna can be easily built with printed circuit board fabrication technique and applied in low profile multiband base stations for 2G/3G/4G and the next generation systems.

A low-profile linearly polarized antenna based on artificial magnetic conductor (AMC) is proposed. Triangle cuttings and Π-shaped slots are introduced on a traditional double-sided printed rectangular dipole antenna to realize ultrawideband characteristic and miniaturization. A novel 6 × 6 AMC array is proposed for the purpose of reducing the profile of the dipole. The AMC unit consists of a circular patch with four groups of symmetrical edged slots. Experimental results for the proposed antenna exhibit a 40% impedance bandwidth (4.77–7.12 GHz), maximum gain of 9.9 dB, and a front-to-back ratio of approximately 25 dB. The total height is 6mm (0.12 λ ₀ at 6 GHz). Compared to the slotted dipole antenna with perfect electrical conductor, the profile is reduced from 0.19 λ ₀ to 0.12 λ ₀ . This antenna with the advantages of simple-fed structure, low cost, easy fabrication can be a good candidate for C band communications.

In this paper, a novel planar structure-shared diverse two-port ultra-wideband (UWB) antenna with high isolation and common ground is proposed based on a new slot-loaded method. A tapered slot with end-fired radiation pattern is etched in the top middle section of a coplanar waveguide (CPW)-fed printed monopole antenna to reduce its effects on monopole mode. The two-port UWB antenna features diverse patterns which can fully cover the upper space. A nonuniformly symmetric coupled coplanar waveguide (NSC-CPW) is introduced to enable two sets of the feeding structures sharing a ground plane with minimum interaction. Due to the modal orthogonality, high isolation between the two ports is obtained without additional decoupling structures. Experimental results of the proposed MIMO antenna indicate that the isolation is higher than 31.4 dB and the diversity gain is approximately 10 dB within a wide frequency range from 2.98 to 10 GHz. Meanwhile, high realized peak gain (> 2.5 dB) and good efficiency (> 80%) are also obtained for both two ports.

In this paper, we present a systematic approach to design a compact dual-mode monopole-like patch antenna using characteristic mode analysis (CMA). The modal analysis of a slotted circular patch structure incorporating a new shorting pin loading technique is presented. To achieve a compact monopole-like antenna with wideband operation, it is demonstrated that the first two significant modes with monopole-like patterns are the most suitable ones for dual-mode excitation. Based on the analysis of the modal currents and electric fields, four groups of shorting pins and four slots are introduced to individually tune the two modes, which facilitates the optimization. The effects of these slots and shorting pins on the resonant frequencies of the two modes are analyzed in detail. Finally, a CPW T-junction power divider is applied to simultaneously excite these two modes and suppress the undesired modes. Apart from a more compact form factor and higher gain than existing work, it also features a competitive gain-bandwidth per volume ratio.