A novel wide-angle beam scanning phase synthesis method, namely, multi-beam phase matching method (PMM) is introduced in this paper. It takes full advantage of angle sensitiv-ity characteristic of reflectarray elements to improve the beam scanning performance of reflectarrays. In the process of reflec-tarray aperture synthesis, the beam deviation factors (BDF) and reference phases are optimized to minimize the total phase error, and the geometries of each element are optimized to match the desired phase shifts at multiple beam scanning angles after taking into account the real incident angles. Then, a 16×16-element re-flectarray antenna with square patch elements operating at 12GHz has been designed, simulated and fabricated. The meas-ured results show that a gain variation less than 1.7dB across the scan coverage from -45° to +45° can be achieved by mechanically rotating the feed antenna, which shows a considerable improve-ment in beam scanning performance as compared to the reflec-tarrays designed using conventional single-focus and bifocal methods.

In this paper, a novel 3-dimensional (3-D) printed circularly polarized (CP) modified Fresnel lens antenna operating at 300GHz is introduced. By virtue of the superior geometric flexibility of the 3-D printing technique, a modified Fresnel lens consisting of subwavelength discrete dielectric posts in the odd-numbered Fresnel zones is proposed. It is further demonstrated that by integrating dielectric anisotropic metamaterial, the modified Fresnel lens can realize CP radiation fed by a simple linearly polarized (LP) open-ended waveguide (OEWG). The 3-D printing approach is also investigated to push the performance envelops of the 3-D printer for realization of the THz CP lens. The measured results show that the axial ratios (AR) of the fabricated antenna prototype are smaller than 3dB from 265 to 320GHz. Moreover, the modified Fresnel lens has a maximum gain of 27.4dBic, which is 0.9dB lager than that of the conventional Fresnel zone plane antenna (FZPA). These validate the concept, the design, and the fabricated prototype.

A broadband single layer, dual circularly polarized (CP) reflectarrays with linearly polarized feed is introduced in this paper. To reduce the electrical interference between the two orthogonal polarizations of the CP element, a novel subwavelength multiresonance element with a Jerusalem cross and an open loop is proposed, which presents a broader bandwidth and phase range excessing 360° simultaneously. By tuning the x- and y-axis dimensions of the proposed element, an optimization technique is used to minimize the phase errors on both orthogonal components. Then, a single-layer offset-fed 20 × 20-element dual-CP reflectarray has been designed and fabricated. The measured results show that the 1-dB gain and 3-dB axial ratio (AR) bandwidths of the dual-CP reflectarray can reach 12.5% and 50%, respectively, which shows a significant improvement in gain and AR bandwidths as compared to reflectarrays with conventional λ/2 cross-dipole elements.

A low-profile dual-polarized wideband omnidirectional antenna with artificial magnetic conductor (AMC) reflector is proposed. The proposed antenna is operated in the long term evolution band (1.7-2.7 GHz), and has a compact size of 200 mm × 200 mm × 30.6 mm (about 0.25λ height at 2.7 GHz). The antenna structure consists of a horizontally polarized circular loop antenna, a vertically polarized lowprofile monopole antenna, and an AMC reflector. By carefully designing the reflection characteristics of the AMC reflector, the profile height of the proposed antenna is significantly reduced as compared with those of antennas backed by conventional perfect electric conductor (PEC) ground planes. Simulated and measured results show that the proposed antenna is able to achieve over 45% impedance bandwidth (VSWR <; 1.8) with stable radiation patterns in the band of 1.7-2.7 GHz. Owing to the attractive wide bandwidth, low-profile configuration, and ease of fabrication, the proposed antenna is suitable for microbase station systems, especially for indoor ceiling antenna networking applications.

A wideband linearly polarized transmitarray antenna operating in 7-16 GHz is presented in this paper. First, a wideband element with three metallic layers is proposed, which is composed of a split circular ring connected by a narrow strip in the middle layer, and two polarizers in the upper and bottom layers. This element features a low transmission loss and approximately linear phase curves in a wide frequency band over one octave. Then, an optimization method is introduced to design the transmitarray that follows the bandwidth definition of 1 dB gain drop. The first key point of this method is determining the transmitarray element distribution with the weighted reference phases. The second is realizing wideband performances by controlling the calculated directivities and radiation patterns of the modified wideband transmitarray model at all operating frequencies. In the experiment, a 25×25-element horn-fed transmitarray with a 240 × 240 mm ² aperture area is designed and fabricated. The simulated results show that its bandwidths of 0.5, 1.5, and 3 dB gain drop are 41%, 56%, and 71%, respectively. Moreover, a peak aperture efficiency of 40.7% is achieved. Measured results agree reasonably well with the simulated ones. These results validate the proposed wideband element and the optimization method.

Conformal antennas are practicable candidates to the aerodynamic platforms. A wide-angle scanning conformal phased array antenna for an unmanned aerial vehicle (UAV) platform is designed and presented in this article. An eight-element linear phased array loaded with frequency selective surface (FSS) operating in S-band is investigated. The horizontally polarized antenna element is designed based on a tapered slot feeding dipole. The antenna aperture can be easily conformed to the front wing airframe of the UAV due to the flexibility of the employed polyimide film. To fulfill the requirement of the airborne communication system, two kinds of FSSs are loaded on the dipole antenna to enhance the gain and reduce the 3 dB beamwidth of the main lobe in the elevation plane. To improve the active impedance matching when the beam scans to the large angles, a novel parasitic structure is proposed. Finally, a 1 ×8 linear conformal array prototype is simulated, fabricated, and measured. The experimental results indicate that the antenna array achieves a fractional bandwidth of 22.1% with ±70° scanning along the E-plane. The measured results validate the performance of the proposed conformal array and the design.