A parasitic coupling network concept for mutual coupling utilization in wideband multielement antenna arrays

Abstract

A novel approach to widening the active reflection coefficient (ARC) bandwidth of an antenna array, employing a parasitic coupling network (PCN), is investigated in this article. Different from traditional tightly coupled arrays adopting space structures for enhancing the coupling in balanced-excitation antennas, a PCN derived from rigorous formulas is employed in the feeding lines of unbalanced-excitation ones. Based on network analysis, the mutual coupling utilization condition for an (M×N)-element antenna array is initially deduced, and the PCN is implemented. Then, the PCNs are realized by introducing a parasitic element and a coupling network between the two-element H-plane and E-plane dual-layer coupled microstrip antenna arrays, resulting in 10.9% and 30.8% bandwidth enhancements compared with the original arrays, respectively. Moreover, the PCNs are further expanded to multielement antenna arrays, including three- and five-element one-dimensional and 8×2 two-dimensional arrays, exhibiting approximately 40% overlapped ARC bandwidths with normal radiation patterns, steady gains, and applicable scanning characteristics. The results indicate its potential application in large-scale wideband arrays.

1. Introduction

Mutual coupling manipulation is always an awkward issue for antenna array design, as coupling between array elements can trigger the deterioration of antenna performance, including impedance matching, radiation pattern, gain, sidelobe level, and scanning characteristics (Allen and Diamond, 1966; Guo et al., 2020). Therefore, many studies have been carried out on suppressing mutual coupling, and plentiful techniques have been proposed to achieve high isolation between elements, which can be divided mainly into two categories. One category is field methods, such as defected ground structure (DGS) (Kumar C et al., 2017), frequency selective surface (FSS) (Zhu et al., 2021), electromagnetic bandgap (EBG) (Zhai et al., 2016), single negative (SNG) metamaterial (Bait-Suwailam et al., 2010) and metasurface (Liu et al., 2020), array-antenna decoupling surface (ADS) (Wu et al., 2017), and parasitic decoupling (Lau and Andersen, 2012; Ghadimi et al., 2020; Kumar P et al., 2023). Here, parasitic decoupling mainly reduces mutual coupling by introducing parasitic structures between array elements to counteract the coupling field or current; thus, the radiation performance can be greatly improved.

The other category is circuit methods, covering decoupling networks (Zou et al., 2019, 2023; Wang ZT and Wu, 2023) and neutralization lines (Li M et al., 2020). However, mutual coupling can also be used to improve the antenna performance. According to the operating mechanism of the loaded structure, mutual coupling utilization methods can be divided into space and network ones.

The most typical example of space mutual coupling utilization is a tightly coupled array (TCA), the concept of which is derived from the infinite current sheet array (CSA) proposed by Wheeler (1965) and developed by Munk et al. (2003), who discovered that, through introducing coupling components to the end of the closely arranged dipoles, the antenna array could exhibit wideband characteristic. Since then, copious works concerning TCA have been carried out to expand the bandwidth of the antenna array and wide-angle scanning range (Holland and Vouvakis, 2012; Chen et al., 2021; Li WT et al., 2023; Zhang et al., 2023). After initially being employed in dipole arrays, TCA has been further expanded to other balanced-excitation antenna arrays, the elements of which are usually symmetric with two arms and are fed by the same amplitude and a 180° phase difference (Holland and Vouvakis, 2012), including Vivaldi array (Reid et al., 2012) and spiral antenna array (Alwan et al., 2012). However, for unbalanced-excitation antennas, the concept of mutual coupling utilization is scarcely introduced.