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A wide axial-ratio beamwidth (ARBW) and half-power beamwidth (HPBW) circularly polarized (CP) antenna is realized by arranging two curved patch dipole pairs orthogonally in a cruciform contour that conforms with a hemispheric shell. First, two orthogonal curved dipole pairs are designed via step-by-step investigation of the evolution of traditional crossed dipoles. Then, an antenna with a wide CP working bandwidth and wide ARBWs and HPBWs is developed by enlarging the diameter of the curved arms, replacing the narrow arms with the wide patches and making these patches conformal with the shell surface; this improves the impedance bandwidth (IBW) and further reduces the antenna’s size. Finally, a prototype with reduced dimensions of $0.52\times 0.52\times0.15$ ( $\lambda _{0}^{3}$ ) is designed, fabricated, and measured. The resulting antenna exhibits a −10 dB IBW of 55.8% (1.06–1.89 GHz) and a 3 dB AR bandwidth of 70.9% (1–2.1 GHz), within which the ARBW and HPBW reach maximum values of 202°/196° and 113°/111° in the two orthogonal principal planes at 1.602 and 1.268 GHz, respectively. Furthermore, a 3 dB ARBW exceeding 100°, an HPBW exceeding 96°, and efficiency exceeding 60% are acquired within the 1.252–1.89 GHz (40.6%) target service coverage band.

A wideband and compact Fabry–Perot resonator antenna (FPRA) employing two layers of partially reflective surfaces (PRSs) is presented in this letter. The proposed PRSs with regular hexagonal units are used in wideband FPRA for the first time. Based on the compact arrangement of regular hexagon units and the addition of tripod branches, the size of FPRA is greatly reduced. Furthermore, the regular hexagonal units are arranged periodically along three directions on the 2-D plane, which means that one regular hexagon unit has six identical units around it. Therefore, there is a strong coupling between the PRS units, and units obtain a positive phase gradient in a wide range of 9.1–13.5 GHz, which is the basis for the formation of the wideband FPRA. The FPRA with dimensions of (2.2×2.2×0.6) λ03 (λ0 is the wavelength of the center frequency) has a 3 dB gain bandwidth over 9.2–13 GHz, relatively 34.2%, with a peak gain of 14.2 dBi. The prototype has been fabricated and tested, and validate the simulated results.

In this letter, a broadband 1 bit reconfigurable transmitarray antenna (RTA) based on polarization rotation element is proposed. The transmitarray element is composed of two split circular rings connected by two narrow strips and sandwiched by two orthogonal polarizers. As phase shift and polarization conversion structure, the two patches are separated by the air layer, and the p-i-n diodes are soldered in the center of the narrow strips. The polarizer grids are used as dc bias lines to conduct p-i-n diodes. By controlling the p-i-n diodes in the on and off states, the polarization orientation of the wave emitted by the RTA element is changed. Then, the outgoing waves in the two states physically form a broadband 180° phase difference, which broadens the operating bandwidth of the RTA effectively. By utilizing the novel unit cell, a 16 × 16 elements RTA is designed, fabricated, and measured. The measured results show that the 3 dB and 1 dB gain bandwidths are 45% and 17%, respectively. The peak gain is 16.8 dBi with aperture efficiency of 18.4%. Furthermore, the proposed RTA has good beam scanning performance with 2-D scanning range of ±40°.

In this paper, decoupling of a compact isosceles triangular array is performed by a hybrid method consisting of loaded parasitic element (LPE) in combination with decoupling and matching network (DMN). By introducing a reactively loaded parasitic element at a suitable position on the axis of symmetry of the isosceles triangle, not only are the mutual couplings between the element at the vertex and the two elements on the base eliminated but also the circuit parameters of the base elements are well prepared for a DMN of a simpler form. Thus, the impedance matching of the vertex element and the decoupling and matching of the base elements can be implemented independently. The DMN of base elements comprises two impedance-transforming sections (ITS) and a $\pi $ -shaped neutralization section (NS). The ITSs inserted between the antennas and NS convert the self-conductance to the system admittance and the trans-conductance to zero. The trans-susceptance is then compensated through the main line of the NS independently, and self-susceptance is canceled out by adjusting the tapped stubs subsequently. With all the explicit formulas derived, the design is systematic and straightforward. The presented compact isosceles triangular array with element separations of $0.1\lambda $ and $0.2\lambda $ is fabricated and measured. The results show that sound isolation of 35 dB and return loss of 21 dB is obtained with ECCs less than 0.02, validating the effectiveness of the hybrid decoupling technique.

In this letter, a design method of dual-band filtering baluns is presented. The filtering balun operating in 2 bands have the characteristic with flexible frequency ratio in this approach. By properly introducing dual-mode resonators, the filtering balun can work at 2 bands and the frequency ratio of these 2 bands could be flexibly controlled. To prove the effectiveness of the proposed design principle, a dual-band filtering balun working at 3.5 and 4.7 GHz is designed and simulated. Eventually, the results of simulation exhibit favorable performance.

An octagonal prism conformal antenna array for x-band with vertically polarized omnidirectional radiation pattern is presented in this letter. The proposed antenna consists of a feeding network, radiation patches, parasitic patches, and dielectric layer. The 16 patches are placed on the outer surface of the octagonal cylinder and fed by a feeding network with uniform magnitude and phase. The patches are divided into upper and lower layers, each of which has eight units. Thus, the proposed antenna can obtain an omnidirectional radiation. To enhance the isolation between the elements, slots are introduced to decrease electromagnetic coupling between elements through the medium. By utilizing 16 conformal patches, the gain in the horizontal plane can be improved, especially for the range of $\boldsymbol{\theta}=80^{0}$ to $\boldsymbol{\theta}=100^{0}$ . The proposed antenna is designed and simulated. Simulation results reveal that the proposed antenna can provide an impedance bandwidth of 20% (7.16–8.76 GHz). Additionally, the minimum gain of the range which from $\boldsymbol{\theta}=80^{0}$ to $\boldsymbol{\theta}=100^{0}$ is greater than 2.8 dBi over the frequency band.

A wideband omnidirectional vertically polarized antenna is proposed which mounted on an unmanned aerial vehicle (UAV). The antenna adopts the structure of the printed dipole array back to back microstrip patches which fed by coaxial cable. The antenna is loaded by two shorted pin and realized characteristics of low profile and vertical polarization. The patch radiators and feed lines on one side of the ground plane are reversed in positions compared to the other side, and hence with radiators on both sides an azimuthal omnidirectional pattern is formed. The antenna realizes omnidirectional radiation in the horizontal plane. The antenna has a measured $\vert \mathbf{S}_{11}\vert bandwidth of 3.9-5.0 GHz (24.7%). The prototype antenna can be widely used in the field of communication antenna on unmanned aerial vehicle for its advantages of simple structure, small wind resistance, omnidirectional patterns, and low profile.

A circularly polarized (CP) antenna which is a set of 2×2 patch array with parasitic rectangular elements is designed and measured. The parasitic patch can enhanced the gain of the antenna. Each antenna element is fed by two probe that is connected to the feeding network. The final design, with an overall size of 160mm×160mm×28mm $(\sim 1.1\lambda_{0}\times 1.1\lambda_{0}\times 0.2\lambda_{0}$ at 2.09 GHz), was fabricated and measured. The proposed antenna has been fabricated and measured. The antenna array has a measured $\vert \mathrm{S}_{11}\vert dB bandwidth of 1.82-2.4 GHz(27.5%), the 3-dB axial-ratio(AR) bandwidth of 1.9-2.2 GHz is also obtained. Besides, the peak gain of the antenna array is 13.46 dBi at 2.01 GHz.

In this paper, a new design of an dual-band printed quadrifilar helical antenna(QHA) for S-band has been presented. This quadrifilar antenna has four helical arms wrapped around a dielectric cylinder which has low permittivity and low loss. Each arms consists of two parallel elements long and short which opened at the top of the helix. The lower end of helix is simultaneously fed, the long element resonates at 1.995GHz (1.98GHz–2.01GHz with the center frequency 1.995GHz), and the short element resonates at 2.185GHz(2.17GHz–2.2GHz with the center frequency 2.185GHz). The four arms are fed with equal amplitudes with 0°, 90°,180°,270° phase by integrated feeding network. Simulated results of the proposed antenna show that the antenna can provide good wide-beam circular polarization characteristics in both frequency bands. The proposed antenna has a smaller size, light weight and low cost to be suitable for mobile handset applications.