ABSTRACT A millimetre‐wave (mm‐wave) microstrip patch antenna with a stable wide beamwidth is proposed for a wide‐angle scanning phased array. The proposed antenna element is achieved by loading four semi‐open parasitic elements around the stacked patch. The four semi‐open parasitic elements can generate two pairs of stable antiphase current radiation sources to achieve a stable rotated ‘8’‐shaped pattern, which can obtain wide‐beamwidth radiation patterns when it is synthesised with the broadside radiation pattern produced by the stacked patch. Further, the coupling between the parasitic elements and the driven patch producing the lower reflection zero is weaker than that between the parasitic patch producing the upper reflection zero. Therefore, the proposed antenna can achieve a stable wide beamwidth over wide frequency ranges. The generation of the rotated ‘8’‐shaped pattern is theoretically analysed. An eight‐element E ‐plane scanning linear antenna array based on the proposed antenna element is demonstrated for the potential application in a wide‐angle scanning phased array. The simulated and measured results show that the main beam can scan from −75° to 75° with a gain fluctuation &lt; 3 dB under a 10‐dB fractional bandwidth of 16.7%. 

Millimetre‐Wave Microstrip Patch Antenna With Stable Wide Beamwidth for Wide‐Angle Scanning

Abstract A wideband Magneto‐Electric Dipole (MED) antenna with high gain is proposed for the 700/800/850/900 MHz frequency bands for cellular network applications. The antenna comprises a half‐wavelength bow‐tie‐shaped dipole, an elongated magnetic loop and a ground reflector with four Elevated Ground Planes (EGPs) at reflector's corners. The EGPs enhance the antenna gain and Front‐to‐Back Ratio (FBR), which is a promising technique in the MED antenna design. The antenna is excited by a ‐shaped coupling element. An analytical model of the proposed antenna is developed by employing Schelkunoff's model for dipole antennas and the transmission line theory complemented by radiation resistance corrections. The antenna design is validated with full‐wave numerical simulations. The antenna is fabricated using cut and bent metallic plates and tested in an anechoic chamber. The analytical, numerical and experimental results are in a good agreement. The experimental results confirm that the proposed MED antenna with dimensions of achieves a bandwidth of 61.53% (623.1–1176.8 MHz) for and a stable gain of 9.8 1.9 dBi. By employing the EGPs, the realized peak gain and FBR are enhanced by 0.52 dBi and 1.1 dB, respectively. 

Modeling and Design of Improved‐Gain Wideband Magneto‐Electric Dipole Antenna for Micro‐BTS Applications

Training an optimal policy in deep reinforcement learning (DRL) remains a significant challenge due to the pitfalls of inefficient sampling in dynamic environments with sparse rewards. In this paper, we proposed a Human Local Guide (HLG) incorporating high-level human knowledge and local policies to guide DRL agents to achieve optimal performance. HLG deployed the heuristic rules from human knowledge in differential decision trees and then injected them into neural networks, which can continuously improve the suboptimal global policy till the optimal level. Our developed HLG includes action guides based on a policy-switching mechanism and adaptive action guides inspired by an approximate policy evaluation scheme through a perturbation model to optimise policy further. Our proposed HLG outperforms PPO and PROLONET with at least 25% improvement in training efficiency and exploration capability based on MinGrid environments with sparse reward signals. This implies that HLG has a significant potential to continuously assist the DRL agent in achieving optimal policy in dynamic and complex environments.

HLG: Bridging Human Heuristic Knowledge and Deep Reinforcement Learning for Optimal Agent Performance

This brief presents a miniaturized wideband circularly polarized magneto-electric dipole antenna using <inline-formula> <tex-math notation="LaTeX">$\Psi $ </tex-math></inline-formula>-shaped phase shifter. Its magneto-electric dipole structure utilizes four L-section patches attached to outer edges of four square patches to achieve miniaturization. A parasitic patch positioned above the dipole structure is employed as an impendence transformer to extended the bandwidth. Meanwhile, a notched cavity equivalent to four magnetic dipoles is set around the dipole structure to enhance the beamwidth. To achieve circularly polarized wave, a feeding network composed of four-order Wilkinson power divider and <inline-formula> <tex-math notation="LaTeX">$\Psi $ </tex-math></inline-formula>-shaped phase shifter is designed to realize two equal-amplitude outputs with 90° phase difference. The <inline-formula> <tex-math notation="LaTeX">$\Psi $ </tex-math></inline-formula>-shaped phase shifter utilizes an open-short stub combining open circuit and short circuit, then achieving 106.9% impendence bandwidth with low insertion loss of 0.03 dB at 1.5 GHz. Then, the proposed antenna is fabricated with a compact size of <inline-formula> <tex-math notation="LaTeX">$0.5{\lambda }_{0} \times 0.5{\lambda }_{0} \times 0.3{\lambda }_{0}\,\,({\lambda }_{0}$ </tex-math></inline-formula> at 1.5 GHz). The measured results show that its impedance bandwidth is 94.6% while the 3-dB axial ratio bandwidth reaches 107.1%. The maximum half-power beamwidth reaches 144°/135° at -45°/45°-plane within the band from 0.78 GHz to 2.15 GHz while maximum axial ratio beamwidth respectively obtains 182°/203° in -45°/45°-planes.

A Miniaturized Wideband Circularly Polarized Magneto-Electric Dipole Antenna With Wide Beamwidth Using Ψ-Shaped Phase Shifter

While Deep Reinforcement Learning (DRL) has emerged as a prospective method to many tough tasks, it remains laborious to train DRL agents with a handful of data collection and high sample efficiency. In this paper, we present an Adaptive Fuzzy Reinforcement Learning framework (AFuRL) for accelerating the learning process by incorporating adaptive fuzzy logic rules, enabling DRL agents to improve the efficiency of exploring the state space. In AFuRL, the DRL agent first leverages prior fuzzy logic rules designed especially for the actor-critic framework to learn some near-optimal policies, then further improves these policies by automatically generating adaptive fuzzy rules from state-action pairs. Ultimately, the RL algorithm is applied to refine the rough policy obtained by a fuzzy controller. We demonstrate the validity of AFuRL in both discrete and continuous control tasks, where our method surpasses DRL algorithms by a substantial margin. The experiment results show that AFuRL can find superior policies in comparison with imitation-based and some prior knowledge-based approaches.

Accelerating Deep Reinforcement Learning Under the Guidance of Adaptive Fuzzy Logic Rules

A wideband high-efficiency metal-only folded reflectarray antenna (FRA) using 3-D subwavelength detachable trapezoidal grooved element (SDTGE) is proposed in this communication. The presented element is made up of two orthogonally rectangular metal plates etched with two trapezoidal grooves. It allows the reflection phases of the two linearly polarized (LP) waves to be shifted independently by varying the lengths of the grooves. To make a detachable structure, a sliding groove is employed on one of the two metal plates to help assembly. By setting the period to a subwavelength, a smooth phase shift response is obtained to extend the bandwidth. In addition, a large reflection phase variation of 670° at 10.0 GHz and a low element loss of nearly 0 dB are obtained to further enhance the gain. Then, a $35\times 35$ element reflective aperture spatially fed by a 3-D printed pyramidal horn antenna is designed and measured to verify the performance. The measured results exhibit that a wide 1-dB gain bandwidth of 26.5% is achieved. To reduce the profile, a wideband triple-layer polarization selector suspended on the reflective aperture is designed to achieve an FRA prototype. It features a maximum gain of 29.2 dBi corresponding to an aperture efficiency of 51.8% and a 3-dB gain bandwidth of over 34.2%. These results indicate that this metal-only FRA (MOFRA) has advantages of wide bandwidth and high efficiency.

A Wideband High-Efficiency Metal-Only Folded Reflectarray Using Subwavelength Detachable Trapezoidal Grooved Element

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Papers

A Miniaturized Wideband Circularly Polarized Magneto-Electric Dipole Antenna With Wide Beamwidth Using Ψ-Shaped Phase Shifter

Accelerating Deep Reinforcement Learning Under the Guidance of Adaptive Fuzzy Logic Rules

A Wideband High-Efficiency Metal-Only Folded Reflectarray Using Subwavelength Detachable Trapezoidal Grooved Element