An Efficiency-Improved Tightly Coupled Dipole Reflectarray Antenna Using Variant-Coupling-Capacitance Method

In this paper, a tightly coupled dipole reflectarray antenna as well as a variant-coupling-capacitance method to improve the antenna aperture efficiency is presented. Tightly coupled elements and true-time-delay lines are employed in the design of a wideband reflectarray. The proposed reflectarray can operate from 2 GHz to 5 GHz with the gain varying from 11.3 dBi to 21 dBi. Moreover, we propose a variant-coupling-capacitance method to improve the reflectarray aperture efficiency at lower frequency. By changing the coupling capacitance between neighboring elements according to their positions in the reflecting surface, a more linear equivalent distance delay line is achieved. Hence, phase error is reduced. According to measurement, the reflectarray gain in 2 GHz using the proposed method is increased by 3 dBi compared with the previous design. Aperture efficiency in 2 GHz is improved by 21.6%

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Capacity Enhancement by Pattern-Reconfigurable Multiple Antenna Systems in Vehicular Applications

This work presents a design methodology for pattern reconfigurable antennas in automotive applications. Channel simulation is used to identify the relevant beam directions prior to the design of the antenna. Based on this knowledge several reconfigurable multiple antenna systems are designed. These antennas are evaluated by the channel capacity calculation from virtual and real-world test drives. An increase of the channel capacity by a factor of 2 compared to a conventional system is observed

Optical Metasurfaces with Advanced Phase Control Functionalities

The development of a metasurface platform with advanced micro- and nano-fabrication techniques has attracted a lot of attention. It exhibits a broad range of applications in the lens, hologram, image processing, vortex beam generation, information encoding, sensing, etc. Metasurfaces are ultrathin planar nanostructures made of subwavelength metallic or dielectric elements that can efficiently control the light characteristics such as polarisation, dispersion, amplitude, and phase. The high-index dielectric metasurfaces exhibit low loss and produce various types of resonant effects such as Mie-type resonances, Huygens' resonances, and so on. The Huygens' resonant regime of the dielectric metasurfaces exhibits the near-unity transmission window with a 2pi-phase coverage. The efficient 2pi-phase control capability with high transmittance feature makes the metasurfaces versatile tools for wavefront manipulation. The challenge is to realize the practical application of the metadevices such as beam deflection, optical image processing, sensing, hologram, lens, and so on. The performance of such metadevices can be made highly efficient by incorporating carefully engineered phase discretisation. Due to such engineered subwavelength wave discretisation, new functionalities that are not possible to date can be achieved by governing the phase response. In this thesis, I will first demonstrate the efficient control of deflection angle with high diffraction efficiency in the visible wavelength. I will also discuss deeply subwavelength metasurface resonators for terahertz wavefront manipulation. Then, I will focus on a novel dielectric resonant metagrating-based highly sensitive optical biosensing technique. Finally, I will demonstrate Mie-resonant dielectric metasurfaces can be used as a passive filter to perform image processing in the form of edge detection of a target object