## 1 Introduction  
In the last decade, a large variety of wireless enabled portable devices such as smartphones, tablets or laptops have been introduced. The implementation of new mobile technologies further increases the bandwidth requirements of wireless systems in order to cover recently allocated LTE and 5G frequency bands [1]. Recent research works have allowed us to develop the design of antennas using textile materials in the substrate, leading to devices called \"wearable antennas\" [2]. One of the main advantages of the antennas based on textile materials is that they can be manufactured using smart fabric and interactive textile systems [3], in which unobtrusive integration of electronic components increases functionality of the garment [4, 5]. Recently, the implementation of different kind of antennas in wearables has been massive [6, 7, 8, 9]. Microstrip patch antennas are frequently used in textile materials because of their many advantages,such as low profile, light weight, and conformity. However, these kind of antennas suffer from important issues in their design process (precise value and model of fabric dielectric constant for simulations, difficulty to glue metallic parts to textile materials, bending and moisture influence in antenna performance, etc. ), causing severe limitations in their practical applications. This fact is even more dramatic in the frequency bands of modern communication systems based on LTE and 5G technologies. The number of parameters to be tuned in order to make the antenna feasible for working in LTE and 5G applications is usually very high. In these cases, classical optimization methods are no longer suitable, and the employment of advanced optimization algorithms (mainly meta-heuristic approaches, among others) has been shown to be very useful for antenna design [10; 11; 12; 13; 14]. In this paper, we propose a new model of microstrip textile patch antenna, a multi-band device that can be tuned for LTE and 5G services, among others. Specifically, the proposed antenna is composed by a rectangular microstrip patch with two concentric annular slots and a U-Shaped slot, with sleeved meanders introduced in the ground plane to modify the surface current distribution, leading to a bandwidth improvement [15; 16; 17]. This original shape allows the antenna to work accurately in several frequency bands, including LTE and 5G communication services. On the other hand, this specific shape also leads to a hard optimization problem, with a high number of real variables and constraints to be taken into account. Moreover, the proposed antenna has been simulated considering a wearable substrate, which makes the direct designing process even more difficult. A meta-heuristic algorithm for optimization is then considered in order to obtain a good design of the antenna, with excellent properties of bandwidth in all the considered frequency bands. Therefore, we propose to use a version of the Coral Reefs Optimization (CRO) algorithm [18]--in this case, the version with the substrate layer (CRO-SL) approach [19]. The CRO is an evolutionary type algorithm which simulates all the processes occurring in a real coral reef in order to carry out the optimization of a given system (the textile antenna considered in this work in this case). The CRO-SL version has been successfully applied to a number of optimization problems [19], and it is able to combine different search patterns or strategies within a single population of potential solutions. In this case, we will show how this optimization scheme is able to obtain excellent results in the optimization process of the proposed antenna, tuning it for its use in LTE and 5G communication systems. In the experimental section of the paper, we detail the antenna design process and its simulation with specific software in order to evaluate the potential of the CRO-SL in this design problem. The rest of the paper is structured in the following way: the next section presents in detail the proposed antenna design, characteristics, and variables to be optimized.