A novel dual-polarized antenna with very low profile using non-uniform meta-surface is presented in this letter. The proposed antenna is composed of two dipoles placed crosswise of which the radiators are formed by four square metal plates. The antenna is designed to work at the lower frequency band (0.69-0.96 GHz) of base-station. By adding the meta-surface atop of the dipole antennas, the overall height of the antenna together with meta-surface can be reduced to $0.1 \lambda_{0}$ (wavelength of the center frequency), which is much lower compared to the normal height of a dipole antenna $(0.25 \lambda_0)$ . Simulated and measured results show that the height reduction is achieved without degrading the performance of the antenna, making the proposed antenna a competitive candidate for base-station application.

This letter presents a broadband 3-D-printed circularly polarized (CP) spherical Luneburg Lens (LL) with linearly polarized feed antenna for X-band. In order to implement spatially continuous varying effective refractive index (RI), the proposed LL is divided to many unit cells and their effective RI is simulated and calculated by effective medium theory. Since the effective RI of unit cells is anisotropic for two orthogonal linearly polarized (LP) waves, the proposed LL is a LP to CP polarizer realized by properly selecting the radius of the LL. The whole structure is fabricated by low cost 3-D-printing (3DP) technic, which is fed by a LP antenna source rotated to a certain angle with respect to the LL around the normal. The measured results indicate that the VSWR, axial ratio and gain enhancement are lower than 2, less than 2.8 dB, and more than 10 dB at X-band, respectively. The results of measurement agree well with the simulation.

From the characteristic mode point of view of electrically small antennas, radiation efficiency normally decreases significantly if multiple modes are well excited. Amongst all these well-excited modes, the one with the lowest modal radiation efficiency determines how much actual radiation efficiency is guaranteed. Based on this idea, this letter proposes a method for improving antenna efficiency using shape optimization approach. The optimized shape can give rise to a high efficiency and an implied high gain after being excited using a single port whose location is easily selected by observing characteristic mode current distributions.

Micro-motion characteristics of conical-shaped high-speed moving targets are presented using the Lorentz finite-difference time domain (Lorentz-FDTD) method. This research discusses the transformation formulas of the space and time increments, the incident wave, the field components between the moving system, and the laboratory system in case of a micro-motion target. The validity and accuracy of the proposed transformation formulas are verified by presenting results for a moving cone and a hemisphere-cylinder combination target.

In this letter, a multibeam leaky-wave antenna (LWA) based on a modified Luneburg lens (LL) beamforming network is proposed. The antenna performs simple structure and low profile with 2-D beam scanning. First, the modified LL serves as a beamforming network, since its variation range ratio of refractive index can be determined by the relative permittivity of the substrate. This can be simply achieved using printed circuit board technique, rather than square root of two of conventional LL. Then, the relationship between the input port angle and the multibeam angle is analyzed using the geometric-optical method. Finally, a high-scanning-rate LWA array based on spoof surface plasmon polaritons is designed, and its open-stopband is effectively suppressed. A prototype is simulated and fabricated. The measured results show that the proposed antenna has a multibeam range of -42° to 40° in the E-plane and a beam scanning range of -53° to 44° in the H-plane within 8-10.5 GHz, which agrees well with the calculation and simulation.

A frequency reconfigurable patch antenna using reed switches to connect the patch with the ground plane is proposed. Compared with other voltage-controlled switches like MEMS and PIN diodes, reed switches are controlled by a magnetic field which can penetrate the ground plane easily. In this way, the control circuit can be placed beneath the ground plane to avoid its impacts on the radiation performance of the antenna. Twenty-four reed switches are used to increase the reconfigurability of the antenna and to show the feasibility of our concept when multiple control circuits are used simultaneously. The presented antenna can be reconfigured to operate in the frequency range from 0.3 to 3 GHz, covering for a large number of communication services. Three operating modes of the antenna (with resonance frequencies at 0.8, 2, and 2.85 GHz, respectively) are presented to illustrate the feasibility of this method. The measured matching and radiation characteristics of the fabricated antenna prototype agree well with the simulations.