# Broadband Flexible Microstrip Antenna Array with Conformal Load-Bearing Structure
## 1 Introduction  
With the benefit of compatibility with the surface of carriers, the conformal antenna can ensure the electromagnetic characteristics of the antenna while effectively meeting the good aerodynamic layout of the carriers [1]. Achieving electromagnetic (EM) radiation characteristics without destroying the original aerodynamic layout of the carrier, the conformal antenna has been used extensively in airplanes, tanks, and various complicated and composite platforms [2]. Due to the increased complexity of the carriers and the diversity of load forms, the requirements for the conformal antenna are different. There are two significant components in the conformal load-bearing antenna (CLA): flexible antennas and a load-bearing structure. On the one hand, the conformal antenna is embedded under the skin of the aircraft with high integration, which demands the design of antennas with a miniaturized structure, stable radiation characteristics, and the capacity to bear dynamic loads [3]. On the other hand, taking manufacturing cost, portability, and life cycle into consideration, the design of a conformal antenna should be simple in structure and flexible in load-bearing [4]. [PERSON] et al. [5] investigated the impact response and damage of theconformal antenna with a load-bearing structure, which indicated the relationship between impact damage and antenna performance, and the impact energy thresholds for acceptable antenna functions were 1.5 and 1.75]. [PERSON] et al. [6] proposed a conformal load-bearing structure for an antenna array and pointed out that a multi-layered structure could be a good candidate for the CLA design. Using a multilayer structure, [PERSON] et al. [7] provided a broadband high-gain bi-layer antenna for CLA application without specific research on mechanical properties. In fact, ongoing research mainly focuses on the design of conformal antenna using flexible material, and the load-bearing structure is ignored [5; 6; 7]. A CLA is developed at the system level, rather than a single design of the antenna [8; 9]. The honeycomb core layer is often applied in the design of the load-bearing structure due to its light weight and great mechanical load-bearing properties. A method for measuring the mechanical properties of the antenna is presented by [PERSON] et al. [9], including tensile, biaxial, and twisting. Nevertheless, experimental verification is lacking. Meanwhile, the conformal load-bearing antenna structure for mechanical loading consideration has been reviewed in this paper. [PERSON] et al. [10] proposed a novel e-fiber antenna embedded in a polymer substrate for load-bearing. The conventional conformal antenna with load-bearing function has been depicted in Figure 1. It is composed of four parts: flexible antennas, honeycomb core layer, upper face sheet, and lower face sheet. Firstly, flexible antennas are in the middle layer as electronic devices. Initially filled between the face sheet and antennas, honeycomb core layers play a crucial role in the load-bearing function. Finally, the upper face sheet and lower face sheet are added as the surface of the conformal load-bearing structure [3; 10]. With the advantages of a lightweight, low-profile, and simple structure, the flexible microstrip antenna array has been broadly applied in the design of various conformal antenna. The narrow impedance bandwidth is the main limitation of the design of conformal antenna [11; 12; 13]. Based on the microstrip antenna, several related technical methods for bandwidth enhancement have been studied and verified. Owing to the diamond-shaped slot, [PERSON] et al. [14] proposed a broadband microstrip antenna with a fractional bandwidth of 13.6%. Through the planar multilayer configuration, [PERSON] et al. [15] provide a feasible solution to improve the bandwidth of the microstrip antenna. However, these methods were employed for rigid materials [14; 15; 16; 17].