A broadband ±45 ^° dual-polarized base station antenna is proposed for 2G/3G/LTE bands. The proposed antenna has Y-shaped feeding lines to impart a wide impedance bandwidth to it, and a rectangular box-shaped reflector to enhance its stability in radiation patterns over the operating frequencies. A prototype of the proposed antenna is designed, fabricated, and tested. The measured results show achievement of impedance bandwidth of 45% for at both ports, port-to-port isolation 25 dB , a stable radiation pattern with 3-dB beamwidth 68 ^° ±2 ^° at H-plane and V-plane, and a stable antenna gain of 8.2 ± 0.6 dBi from 1.7 to 2.7 GHz. A broadband dual-polarized antenna array with five elements for the band is developed for base station application. Measurements show achievement of array gain of 14.8 ± 1.4 dBi, 3-dB beamwidth 66.56 ^° ±2.22 ^° at H-plane at port 1 and 64.85 ^° ±4.96 ^° at port 2 with over the operating frequency band. Simulation results have a good agreement with measurement ones.

Significance: Different from most existing multistable structures whose multiple stable states are achieved through the combinational effect of bistable units, we invent a generic tristable kirigami cuboid. The three stable states have fundamentally distinct geometric configurations and chirality, and the transformation among them can be realized by tension/compression or clockwise/counterclockwise twist. Tessellating the units in series, a family of multistable metamaterials can be constructed, the mechanical behaviors of which are programmable by the unit geometry, the material of the elastic joints, the number of units, and the loading conditions. As a demonstration of the potential applications, a frequency reconfigurable antenna for 5G triple-band communication is developed based on a tristable unit, and the frequency tunability is verified by experiments.

A circularly polarized antenna with wide axial-ratio beamwidth is presented by placing two pairs of parallel dipoles in a square contour. Firstly, our study demonstrates that circular polarization can be achieved at the broadside by setting a 90° phase difference between the vertical and horizontal paired-dipoles. Secondly, the principle of wide-beamwidth circularly-polarized radiation is described under the similarity in polar and azimuthal radiation pattern for a pair of parallel dipoles. After the spacing between two parallel dipoles is studied, the similar radiation patterns in these two orthogonal planes are derived. As such, a wide-beamwidth circular polarization can be achieved by placing the two pairs of parallel dipoles vertically and horizontally while setting a 90° phase difference between them. In final, a circularly-polarized printed antenna is designed and fabricated on a single dielectric substrate. The two arms of its four dipoles are formed on the lower and upper interfaces of the substrate, and they are excited by a 1-to-4 probe-to-microstrip feeding network. Experimental results show good agreement with simulated ones in terms of radiation pattern/gain, axial ratio and returned loss. In particular, the 3-dB axial ratio beamwidth at the central frequency of 1.6 GHz has extended to 126 ° in an angular range from -63° to +63°. The fabricated antenna exhibits a low-profile property with the height of 0.0043 free-space wavelength.

A dual-mode compressed dipole resonating at high-order modes is proposed to enhance bandwidth and directivity by loading the two dipole arms with two stubs. Characteristic mode analysis shows that with by introducing the loading stubs, the fifth-order mode of the proposed dipole shifts close to its third-order mode for achieving a wideband operation with enhanced gain. A prototype is designed to validate the principle and design approach experimentally. The measurements show that the gain of the proposed compressed dipole is 4 dBi, higher than that of a conventional dipole over the desired operating band of 3.3-3.6 GHz for the coming 5G applications.

A novel method of enhancing cross-polarization discrimination (XPD) of a ±45° dual-polarized base-station antenna, by addition of four parasitic elements placed in a square contour, is presented. First, it was established that high XPD at the broadside can be obtained by addition of four parasitic elements around a simple ±45° dual-polarized basestation antenna. Second, we investigated the principle of wide beamwidth high XPD after studying magnitude currents on parasitic element, spacing between parasitic elements and length of parasitic elements. Finally, a ±45° dual-polarized base-station antenna was designed, fabricated and measured. Measurement results are in good agreement with the results of simulation in terms of radiation pattern, gain, and Voltage Standing Wave Ratio (VSWR). In particular, the enhanced XPD is more than 20 dB at the boresight and more than 10 dB within ±60° of the main lobe at the horizontal plane.

A differentially fed dual-polarized multidipole antenna is proposed in this paper. Two pairs of long dipoles and two pairs of short dipoles are printed on an oriental crown-shaped substrate. Through a rational design of positions of dipoles, stable radiation patterns are achieved at the horizontal plane within a relative bandwidth of 45%. Because of the symmetry of the antenna, its differential port-to-port isolation is theoretically infinite. The antenna is designed, fabricated, and measured. The measurement results are in good agreement with the simulated ones in terms of gain, radiation patterns, and voltage standing wave ratio. Wideband impedance matching and stable radiation patterns are achieved by the proposed antenna. In particular, the half power beamwidth (HPBW) at the horizontal plane maintains a mean value 65° with only 4° variations across the desired band, which is suitable for the requirement of a three-sector base-station antenna. Interestingly, the proposed antenna looks like the famous building: the Oriental Crown-China Pavilion in the World Expo held in Shanghai.