# Miniaturized Arrow-Shaped Flexible Filter-Embedded Antenna for Industrial and Medical Applications
## 1 Introduction  
Flexible electronics technologies have emerged as a leading trend in our modern world, recognized as a distinct category of electronics capable of conforming to various surface shapes. These technologies possess unique properties that allow them to bend, twist, and stretch, making them particularly versatile [1]. The proliferation of wearable devices in the electronics market is accelerating, driven by their application across multiple fields, including healthcare, energy harvesting, military applications, and the leisure industry [2, 3, 4]. This surge in interest stems from their unmatched characteristics, which facilitate the seamless integration of flexible electronics into daily activities, ultimately enhancing the quality of human life [5, 6]. As wearable electronics technology continues to advance, ensuring reliable wireless connectivity necessitates the use of flexible antennas. The performance and effectiveness of such devices heavily depend on the characteristics of the integrated antenna [7]. A flexible antenna must be mechanically robust, capable of withstanding high levels of bending, folding, and flexing without degradation. However, these antennas face several challenges, such as resonant frequency variation, which occurs due to changes in effective capacitance when the antenna is bent or rolled [8]. Additionally, as the degree of bending increases, the radiation pattern can become distorted, directly impacting the antenna's gain. Therefore, the design of flexible antennas must address these challenges to ensure consistent functionality in various operating conditions. Furthermore, the antenna should be lightweight and have a low profile to minimize any negative effects [9; 10; 11]. As discussed earlier, antenna designers must address frequency shifts and degradation in radiation characteristics during bending scenarios. To achieve this, highly effective antennas are required. Various types of antennas have been employed for flexible devices, such as microstrip antennas [12], slot antennas [13], planar inverted-F antennas (PIFA) [14], and fractal antennas [15]. Each antenna offers unique advantages and drawbacks based on the desired performance [16]. For example, fractal antennas are often preferred when high performance and miniaturization--up to 75%--are required, along with good radiation characteristics. This preference is due to the enhancement achieved through the modification of the antenna's radiating element geometry rather than the addition of components. This approach reduces complexity, potential failure points, and the overall cost of the antenna [17]. In recent years, several flexible fractal antennas have been reported in the literature. For example, a Sierpinski carpet fractal antenna is presented in [18], which exhibits stable radiation characteristics under bending conditions. However, the substrate used is rather bulky, with dimensions of 70 mm \(\times\) 31 mm \(\times\) 0.075 mm. In [19], a portable and flexible pre-fractal antenna is discussed, offering better control of resonant frequency and improved radiation characteristics. Despite these benefits, the complexity of this antenna design is notably high. Additionally, several interesting works on fractal flexible antennas for energy harvesting applications can be found in [20; 21; 22]. While these antennas demonstrate good performance in terms of impedance and gain, they share a common limitation--narrow bandwidth. Furthermore, electromagnetic interference is another challenge to consider when designing highly efficient antennas for flexible devices. This is because integrated antennas generate detrimental electromagnetic radiation that can cause interference with other systems, thus affecting the performance of the overall system. Therefore, interfering signals must be rejected to avoid transmission degradation [23]. Various techniques are used to suppress harmonic resonances. The most well-known method is to introduce a filter in an RF circuit [24; 25; 26].