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A low-profile wideband tri-polarized MIMO antenna is proposed in this paper. Based on characteristic mode analysis of a circular patch, four slots are etched symmetrically on the patch to transform the high-order monopole-like modes into broadside modes with lower resonant frequencies. Four sets of shorting pins are also applied to simultaneously adjust the resonant frequencies of the monopole-like modes and broadside fundamental modes of the patch. The effects of the slots and the shorting pins on these modes are analyzed in detail. Three dual-resonance ports with high isolation are achieved by exciting three pairs of orthogonal modes of the patch. The proposed antenna is wideband with respect to its profile (bandwidth/height = 216), as facilitated by the dual-resonance property of each port. Experimental results show that the proposed antenna features high port isolation (> 35 dB) and high gain (> 5.58 dB). The proposed low-profile wideband tri-port antenna can be applied in highly integrated MIMO systems.

A probe‐fed dipole antenna with parasitic patches is proposed in this study as the element for wideband and wide‐scanning planar‐phased arrays. Parasitic patches are used to realize wideband performance by significantly reducing the active input impendence. The printed dipole antenna with parasitic patches is directly matched with the subminiature version A (SMA) connector through the modified probe structure. The cell size is 0.5 × 0.5 × 0.145 λhigh3. The planar and low‐profile characteristics make it suitable for modular phased array applications. It is shown that the infinite array simulation results achieve 45.2% bandwidth (7.86–12.45 GHz) with active voltage standing wave ratio (VSWR) < 2 at broadside, 60° scans in E‐, D‐planes and 50° scan in H‐plane. An 8 × 8 prototype array has been manufactured and measured to validate the proposed design and the active element patterns agree well with simulation results.

In this communication, a novel planar structure-shared diverse two-port ultrawideband (UWB) antenna with high isolation and common ground is proposed based on a new slot-loaded method. A tapered slot with an end-fire radiation pattern is etched in the top middle section of a coplanar waveguide (CPW)-fed printed monopole antenna to reduce its effects on the 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 the 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. The experimental results of the proposed multiple-input multiple-output (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 the ports.

A broadband wide-scanning planar phased array is studied in this letter. An accurate equivalent circuit model is used and studied to provide more insights into the working principle of the proposed antenna element. Surface wave suppression is achieved by introducing an air gap, which also improves the active voltage standing wave ratio (VSWR) in H -plane as a wide-angle matching layer. The infinite array cell in simulation achieves nearly 65.2% bandwidth (6.3–12.4 GHz) with active VSWR E - and H -plane. Scanning patterns are measured and show good agreements with simulated results.

In this letter, 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 the 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.

A two-port structure-shared planar ultrawideband (UWB) antenna with high isolation is presented in this communication. 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 the microstrip line and the differential feeding network, respectively. The differential feeding network of the tapered slots excites the 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 the reflection coefficient of the two ports lower than −10 dB and the isolation higher than 38 dB. The measured realized peak gains are above 2.6 dB, and the measured envelope correlation coefficients are less than $9 \times 10^{-5}$ . The proposed UWB multiple-input-multiple-output (MIMO) antenna can be applied in the MIMO communication systems, especially those requiring high isolation.

This paper presents a low-profile coplanar dual-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. The 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 $0.109\lambda _{0}$ at 820 MHz). The measured gains are 13.8±0.5 dB and 16.7 ± 1 dB in lower and upper bands. Large front-to-back ratio (>24.6 dB) and high isolations (>30 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.

The authors propose the design of a compact mechanically frequency and pattern reconfigurable patch antenna. The frequency tuning is achieved by changing the positions of two adjustable shorting screws which are used to modify the length of the antenna radiating patch. Simulated and measured results are carried out to validate the proposed approach. When the screws are symmetrically positioned, the measured operating frequency can be tuned from 2.95 to 5.16 GHz without degrading the radiation characteristics over the entire comparatively wide measured tuning range of 54.5%. The antenna main radiating beam can be tilted from θ = 0° to θ = 30 ° when the screws are asymmetrically positioned. The measured gains and efficiencies range from 3.01 to 5.53 dBi and 68 to 74%, respectively. The overall antenna size is only 0.39 λ 0 × 0.39 λ 0 × 0.02 λ 0 .

We propose a miniaturized design of a four-element dual-band multiple-input–multiple-output (MIMO) 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 λ0 . 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 3.5 and 5.7 GHz with bandwidths of 58 and 43 MHz, peak gains of 2.7 and 2.85 dBi, and peak efficiencies of 63% and 65%, respectively. A considerable measured mutual coupling reduction of 10.8 dB in the lower band and 15.6 dB in the upper band is realized. The overall size of the design is 0.41λ0 × 0.41λ0 × 0.04λ0 with minimum isolation levels of 18.4 and 22.7 dB 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.

Patch antennas with a meandering slot and different distributions of grounded metallic vias are presented in this paper. The meandering slot is adopted to stimulate dual-band operation, while the number and position of the grounded metallic vias are suggested to achieve different radiation performances. The characteristics are analyzed in detail where we find that the existence of the vias also improves the impedance matching. Four samples are designed, where dual-band with both linear polarization, dual-band with circular- and linear-polarization, and single band with linear polarization are obtained, respectively. The samples are finally fabricated and the measurement results agree well with the simulation results.

A wideband dual-polarization patch antenna array is proposed in this letter. The array is fed by a parallel strip line balun, which is adopted to generate 180° phase shift in a wide frequency range. In addition, this balun has simple structure, very small phase shift error, and good ports isolation. The working band of the antenna array is from 1.88 to 2.9 GHz with a relative bandwidth of 41.7%. The height of the antenna array is only $0.144\lambda $ , and the cross polarization is below $- \hbox{20 dB}$ . Two feeding ports are presented, which correspond to two orthogonal linear polarization. The isolation between the ports is higher than 30 dB. The simulation and measurement turns out to be similar. This antenna array can be used in TD-LTE base stations, and the design methods are also useful to other wideband microstrip antennas.