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In this article, a simple dual-polarized antenna with filtering responses and enhanced bandwidth is proposed for base station applications. The antenna concludes three parts: dipole elements, baluns, and a ground plane, which is the same as that of a widely used traditional base-station cross-dipole antenna. By employing only two parasitic elements without using very complicated circuits, the proposed dual-polarized antenna achieves not only filtering response but also widened bandwidth. Each parasitic element produces one transmission zero at higher frequency for the polarization it is associated with, while the other parasitic element produces another transmission zero at lower frequency band for the perpendicular polarization. The two introduced radiation nulls near the passband edge are also controllable. The working mechanism for achieving filtering responses is given. To demonstrate the idea, a simple dual-polarized filtering base-station antenna element is fabricated. The proposed antenna obtains 63% (1.68–3.23 GHz) impendence bandwidth with voltage standing wave ratio (VSWR) less than 1.5. The antenna also features good isolation of more than 32 dB and stable beamwidth variation of less than ±5°. The measured gain within working band is around 8.5 dBi, while the radiation suppression level in stopband is 13 dB. [ABSTRACT FROM AUTHOR]

This paper presents a broadband dual-polarized filtering dipole antenna for base-station application, which has a compact size of 50 $\text {mm} \times 50\,\,\text {mm} \times 31.8$ mm. The antenna consists of four parts: main radiator, feeding baluns, reflector, and two parasitic loops. Without using complex filtering circuits, the dual-polarized dipole antenna realizes satisfactory filtering performance and enhanced bandwidth by employing only two parasitic loops. Two specific radiation nulls are thus generated and individually controlled by the two parasitic loops. To further improve the upper stopband selectivity and bandwidth, a simple open-ended stub is added to the arms of the dipole. As a result, the bandwidth can be tuned from 7.4% to 47.6%, and the realized gain is decreased dramatically from 8.6 dBi at 2.7 GHz (in-band) to −10 dBi at 2.9 GHz (out-of-band). For demonstration, a broadband dual-polarized dipole antenna is implemented. Measured results show that the proposed antenna has more than 34 dB port isolation over 48.7% (1.66–2.73 GHz) impendence bandwidth (VSWR < 1.5). The measured in-band gain is about 8.15 dBi with stable 3 dB beamwidth 65.4°±2.4° in the horizontal plane, whereas the out-of-band radiation suppression is more than 17 dB. [ABSTRACT FROM AUTHOR]

In this paper, a novel decoupling method without adding any decoupling structure is investigated, and it is able to apply to multiple-input and multiple-output (MIMO) antenna designs with dual and multiple elements. The decoupling mechanism applied in here is to change the electrical length of the radiators to manipulate the radiation pattern for obtaining pattern diversity and good isolation simultaneously. The design mechanism and procedures for realizing pattern diversity are presented. To validate the proposed method, a two-element monopole antenna array with inverted-L elements is initially studied with the isolation better than 20 dB. Next, a four-element MIMO antenna utilizing two different types of monopole elements is proposed to further verify the feasibility of the proposed decoupling method. Finally, an eight-element MIMO antenna operating at 3.5 GHz is implemented with a compact total size of $40\times 100$ mm2, and the measured isolations between two elements are better than 15 dB. Envelope correlation coefficient and channel capacity are calculated to evaluate the MIMO performance, and good results are obtained. The target application of the proposed design is for laptop, small cell base station, or WiFi box with multiple elements. [ABSTRACT FROM AUTHOR]

This paper presents a multiple-input and multiple-output antenna using a wideband decoupling structure for enhancing isolation. The decoupling structure is formed by a split ring, which consists of an inductive line and a capacitive gap to realize magnetic and electric coupling, respectively. By introducing the electric coupling in addition to the magnetic coupling, more degrees of freedom are obtained and the original coupling between antennas can be canceled out within a wide frequency band. Meanwhile, the performance of each antenna element is maintained, such as impedance bandwidth and radiation characteristics. Theoretical analysis and experimental verification are carried out. When the decoupling structure is placed between these two monopole antennas with edge-to-edge space of only 5 mm ( 0.04\lambda 0 at 2.5 GHz), more than 20 dB isolation is realized over the bandwidth of 2.3–2.9 GHz (24%) with S11 and S22 less than −10 dB. Moreover, the isolation levels reach more than 30 dB over the frequency band of 2.3–2.8 GHz. Compared with the previous related works using decoupling networks and neutralization line techniques, the proposed decoupling structure can provide higher isolation of over 30 dB in a wider bandwidth. [ABSTRACT FROM PUBLISHER]