Spherical antenna array (SAA) has become highly attractive where hemispherical scan coverage is required as it can provide uniform directivity in all the scan directions. Various direction-of-arrival (DoA) estimation methods suffer from different problems, such as low accuracies in mismatched conditions, high computational complexity and poor estimation in a harsh environment. Another critical concern is mutual coupling (MC) characteristics between the array elements. These problems affect the quality of the navigation signal in harsh environments. This paper presents a robust DoA estimation and mutual coupling compensation technique based on convolutional neural network (CNN) for Spherical Array. Spherical harmonic decomposition (SHD) is used to facilitate feature extraction in two sets, which contains different features about the elevation and azimuth of the source for DoA estimation. The features serve as input to the learning technique for separate estimation of elevation and azimuth, which consequently reduce computational complexity as against the joint estimation of DoA. Learning methods for DoA estimation with few frames and dense search grids within the spherical array configuration are presented. To solve the MC error, the DoA estimation scheme is also used to obtain accurate spectrum peak in the multipath scenario with unknown MC and sharper spectrum peak via the unique structure of the MC matrix and spatial smoothing algorithms. In all, experimental results, which is the ground truth to test any procedure, show the effectiveness, validity, and potential practical application of the proposed technique.

In this communication, a wideband reconfigurable reflectarray based on reflector-backed active second-order bandpass frequency selective surface (FSS) is presented. The reflector is composed of periodic short-circuited parallel plate waveguide (PPW) and the FSS is composed of stacked non-resonant metallic elements separated by thin dielectric substrates. By integrating microwave varactors in the capacitive layers of FSS, more than 270° continuous phase tunability is achieved within a fractional bandwidth of 14%. A one-dimensional reflectarray prototype operating at C band is fabricated and measured. The experimental results show that it can achieve ±55° beam scanning coverage. Symmetric beam steering is observed due to the center-fed configuration. With advantages of low cost and simple structure, the proposed reflectarray can be potentially used in wideband wireless communication and radar systems.

Inspired by animals’ long-distance migration behaviors, we proposed a novel and reliable long-distance true navigation method based on the measurement of geomagnetic fields. By establishing a two-dimensional (2D) gradient approaching coordinate plane with geomagnetic intensity and inclination, long-distance true navigation can be achieved from any starting spots in this area. Without other calibration and auxiliary information, this navigation method is highly independent, which can be used in electromagnetic shielding circumstances, such as deep ocean. The geomagnetic intensity and inclination gradients are estimated with real-time measurement of the geomagnetic field along the navigation trajectory. With estimated local gradients, 2D gradient approaching algorithm can be applied to predict the heading direction, and the agent can press on towards the destination step by step. Theoretical analysis and Monte Carlo simulations verified the feasibility and practicality of this method, proving its robustness in the presence of interference and different measurements errors. It can be a promising candidate in the design of navigation systems used in autonomous underwater vehicles or platform.

Multi-beam system is a core part for wireless concurrent communication and massive MIMO applications. Traditional concurrent communication techniques, like phased-array or digital beam-forming (DBF) system, suffer from massive RF frontends or power-hungry high speed ADCs, which makes them complex and expensive in fabrication. Inheriting the advantages of reflectarray and passive multi-beam system, we reported in this letter a novel and cost-effective concept of steerable simultaneous multi-beam antenna (SMBA). New features and the practicality of it are fully verified with theoretical analysis and experimental implementation of a prototype working at 7GHz with 300MHz bandwidth. With multiple beams steered simultaneously, the SMBA can eliminate the crossover regions between adjacent beams of passive multi-beam antenna. Experimental results indicate its potential in the design of diverse concurrent communication systems such as base stations and point-to-point links.

Wireless power transfer (WPT) is a promising technique used in many applications, like smart terminals, IoT equipment, etc. For wireless power transfer systems based on RF rectifying, working in very low power density situation, high gain rectenna system is of great essential. According to the antenna theory, for the same physical size, higher gain means higher aperture efficiency, which means more power will be received by the antenna instead of being scattered. However, high gain rectenna usually means narrow beam width and high directivity, which is contradictory to a power harvesting system who need to have wide spatial coverage. In order to realize high aperture efficiency and wide spatial coverage at the same time, a 2-D multi-beam rectenna based on gain enhanced patches and hybrid coupler is proposed, which can improve the 2-D spatial coverage and achieve the maximum 81.5% power receiving efficiency. Simulation and experimental results indicate that the power receiving efficiency is more than 50% with 100° coverage in main beam cutting plane, 70° in H-plane, and 90° in E-plane. The practicality of this letter is fully verified, which can help to provide a guidance for the design of rectenna.

In the past decade, many efforts have been devoted to indoor localization solutions. While significant progresses have been achieved, short-range localization of passive moving objects in indoor environments remains a technical challenge, especially when available radio spectrum is limited. In this work, we resolve this challenge by proposing a single-frequency continuous-wave Doppler radar sensor implemented with a redundant single-input multiple-output (SIMO) architecture. Since only Doppler phase shift information is used in the proposed tracking-localization solution, the localization is naturally immune to stationary clutters such as walls and furniture, making this indoor localization only responsive to moving objects. Only using a single frequency is required, such an indoor localization can be implemented with the highest spectrum and energy efficiency. The obtained results imply the potential for the detection of human activities and vital signs in indoor environments with strong stationary scatters.