Dielectric Slabs-Based Lens for Millimeter-Wave Beamforming

This paper proposes a dielectric slabs-based lens for millimeter-wave beamforming systems. The proposed lens is based on the graded steps of the effective refractive index of the semi-spherical lens. It consists of multiple dielectric slabs that match the selected gradient effective refractive index. These slabs have the same thicknesses and different radii. The slab thickness in this lens should not exceed a quarter of the operating wavelength to keep on a similar effective refractive index of the original semi-spherical lens. A horn antenna is used to examine the performance of the designed lens at 28 GHz frequency in terms of the maximum gain, sidelobe level, and 3 dB beamwidth. Sixteen switchable horn antennas are used to demonstrate lens capability for millimeter-wave beamforming. Every single antenna element is selected individually, thus the dielectric lens steers and enhances the corresponding radiation of the selected element in the desired direction.

A Shared Aperture Microstrip Antenna Array with Multiple Polarisations and Near-Field Beam Steering

In this paper we present a shared-aperture polarisation reconfigurable microstrip array designed to resonate at 11.5 GHz with a gain bandwidth of 2 GHz (~17%). The polarisation reconfigurability (both linear and circular) is achieved using two orthogonal and independently-fed sub-arrays that are intertwined together on the same aperture. Each subarray is fed through one port and a feed network that distributes the power among the array elements incorporating Taylor taper distribution to minimize the sidelobe level. The array has low cross-polarisation level (<-20 dB) and good port isolation (<-24 dB). The shared aperture and absence of active switching devices provide better control of polarisation selection with almost no insertion loss. A near-field metasurface based steering system is also presented and applied to the array for one- and two-dimensional beam steering. The results are verified through model simulations and measurement of the fabricated prototypes.

A Shared Aperture Microstrip Antenna Array with Multiple Polarisations and Near-Field Beam Steering

In this paper we present a shared-aperture polarisation reconfigurable microstrip array designed to resonate at 11.5 GHz with a gain bandwidth of 2 GHz (~17%). The polarisation reconfigurability (both linear and circular) is achieved using two orthogonal and independently-fed sub-arrays that are intertwined together on the same aperture. Each subarray is fed through one port and a feed network that distributes the power among the array elements incorporating Taylor taper distribution to minimize the sidelobe level. The array has low cross-polarisation level (<-20 dB) and good port isolation (<-24 dB). The shared aperture and absence of active switching devices provide better control of polarisation selection with almost no insertion loss. A near-field metasurface based steering system is also presented and applied to the array for one- and two-dimensional beam steering. The results are verified through model simulations and measurement of the fabricated prototypes.

An Efficient Adaptive and Steep-Convergent Sidelobes Simultaneous Reduction Algorithm for Massive Linear Arrays

Antenna arrays have become an essential part of most wireless communications systems. In this paper, the unwanted sidelobes in the symmetric linear array power pattern are reduced efficiently by utilizing a faster simultaneous sidelobes processing algorithm, which generates nulling sub-beams that are adapted to control and maintain steep convergence toward lower sidelobe levels. The proposed algorithm is performed using adaptive damping and heuristic factors which result in learning curve perturbations during the first few loops of the reduction process and is followed by a very steep convergence profile towards deep sidelobe levels. The numerical results show that, using the proposed adaptive sidelobes simultaneous reduction algorithm, a maximum sidelobe level of −50 dB can be achieved after only 10 iteration loops (especially for very large antenna arrays formed by 256 elements, wherein the processing time is reduced to approximately 25% of that required by the conventional fixed damping factor case). On the other hand, the generated array weights can be applied to practical linear antenna arrays under mutual coupling effects, which have shown very similar results to the radiation pattern of the isotropic antenna elements with very deep sidelobe levels and the same beamwidth.

Synthesis of low sidelobe level antenna arrays through only main lobe assumption

An analytic method is proposed to design uniformly spaced arrays so that have as low as possible sidelobe level and having directivity as close as to that of uniformly excited arrays. The ideal array factor of arrays is assumed to have only one main lobe. The actual synthesized array would have sidelobe levels which can be controlled by a parameter. Some examples are given to verify the effectiveness of the presented method.

A Low-Sidelobe-Level Variable Inclination Continuous Transverse Stub Antenna with a Nonlinear Slow-Wave Structure

The sidelobe level (SLL) is an essential performance factor for satellite communication antennas. A low-SLL design can effectively suppress adjacent satellite interference. A low-SLL design method for a variable inclination continuous transverse stub (VICTS) antenna is proposed in this paper. The VICTS antenna is composed of three rotatable parts: a feeding plate, a radiation plate, and a polarization plate. The radiation plate comprises two groups of stubs with different radiation ratios. Combined with the nonlinear slow-wave structure attached to the feeding plate, the radiation ratio of the unit can be adjusted. The aperture field of the VICTS antenna using this method can be tapered in order to suppress the SLL. To verify the effectiveness of this method, the antenna prototype is fabricated and measured in a microwave anechoic chamber. The simulation and the measurement are in good agreement. The reflection coefficient of the antenna is kept below −15 dB and between 13.75 GHz and 14.5 GHz. When the radiation plate and the feeding plate rotate relative to each other, the pattern beam can be scanned from 5° to 70 ° . In the scanning range, the typical SLL can reach −18 dB.

Sidelobe level minimization for uniform circular smart antenna array using cultural algorithm

Cultural algorithm (CA) is a new evolutionary program inspired by sociology and archaeology theories that assisting formulating cultural evaluation. Its use to solve optimization problems. This paper analyzed the beamforming of a uniform circular antenna array (UCAA) via using the CA algorithm. The sidelobe level (SLL) is minimized by adjusting the appropriate weight for each element. In addition, the optimal beam pattern is achieved by using CA for UCAA, which means that the main beam is steering to the desired user, while the nulls represent the interference signals. The excitation amplitude is supposed to be constant while the elements are assumed isotropic. The circular array number elements and the interspacing distance between them are setting as optimization parameters. The simulation results show that the CA rationally reacts to the changing environments, and it is valuable for SLL reduction. A −25 dB of relative SLL is achieved under beam scanning (0º) and (15º), respectively.

Theoretical Demonstration of Security Improvement of Optical Phased Array Based on Optically Injection-Locked Lasers

The high security of optical phased array (OPA) signals is an important requirement for OPA-based optical wireless communication (OWC). We propose a method for improving the security of OPA-based OWC systems using optically injection-locked (OIL) semiconductor lasers. We theoretically demonstrate the amplitude and phase modulation of OIL-OPA elements by controlling the injection-locking parameters of the OIL lasers. When a Taylor window function is applied as the amplitude profile of the OPA transmitter, the sidelobe level decreases by 22 dB and the unsecured distance reduces 10 times compared to the case without the Taylor window function. In addition, the unsecured area factor becomes 0.8%.

Performance Enhancement of Reconfigurable Metamaterial Reflector Antenna by Decreasing the Absorption of the Reflected Beam

In this study, a new concept for a Ka-band 5G communication tunable reflector metasurface (MS) for beam steering at 28 GHz is proposed. Varactor diodes are used as the tunability component of each unit cell of this MS. Significant improvements in beam steering and bandwidth performance were achieved using this new concept referred to as the stripes configuration. Several different geometries of unit cells arranged in stripes were designed to achieve better performance in directionality, gain, sidelobe level (SLL), and bandwidth in the stripes configuration. Simulation results for a three-stripe MS with different unit cells in each stripe showed better performance in the phase dynamic range and reduced reflectance losses compared to a typical one-stripe MS. The simulation results showed a significant improvement of 3 dB, depending on the steering angle in reflectance gain, compared to a uniform MS (one stripe). Furthermore, a significant improvement of approximately 50% in the accuracy of the steering angle for different operating frequencies was demonstrated. Manufacturing considerations are discussed in this study.