# An L-Slot Frequency Reconfigurable Antenna Based on MEMS Technology
## 1 Introduction  
Advances in wireless communication technology have led to a shortage of spectrum resources, and the restriction of spectrum resources has led to the development of multi-standard, multi-functional devices. To improve spectrum utilization, cognitive radio (CR) networks use spectrum awareness to detect currently unused frequency bands and adjust their parameters to accommodate free resources to enable normal communication [1]. As a key component in wireless communication systems for sending and receiving electromagnetic waves, antennas are pre-emptively affected. At this stage, solutions in this phase are mainly ultra-broadband, tunable, with high transmission capacity and efficiency, such as broadband antennas, reconfigurable antennas, array antennas, MIMO antennas, etc. Among them, the reconfigurable antenna can dynamically adjust its operating frequency, radiation pattern, and gain according to changes in communication requirements and environment. The adaptive nature of reconfigurable antennas can not only improve the current situation of scarce spectrum resources, but also replace multiple antennas with fixed parameters to reduce the system size and complexity. In addition, it can suppress interference signals in complex radio environments to ensure communication quality. Compared to the limitations of broadband antennas in terms of size, weight, and radiation efficiency, as well as the disadvantages of complex structures and the difficult calibration and maintenance of array antennas, reconfigurable antennas show unique advantages. It can be used in a wide range of systems, such as wireless communications, smart transportation, radar systems, drone swarms, and electronic countermeasures. The key technologies in 5G are wideband and high-frequency transmission. The main operating bands of conventional mobile communications are concentrated below 3 GHz, and the spectrum resources are tight. However, the available resources at high frequencies are abundant and can even occupy a wider continuous operating band to meet the future demand for channel capacity and transmission rate [2]. Because of the ultra-short wavelength of millimeter waves, millimeter wave devices naturally have the advantages of small size and high integration. As a result, multiple antennas can be centrally arranged in a smaller area, which can satisfy both isolation and multi-frequency coverage and high directivity beam allocation techniques. The search for methods to implement high-frequency reconfigurable antennas has become a hot research topic based on current application requirements. Depending on the operating characteristics and application scenarios, reconfigurable antennas can be classified as frequency reconfigurable, directional map reconfigurable, polarization reconfigurable, and hybrid reconfigurable [3]. The reconfigurable implementation methods include using liquid metal [4], carrying tunable material [5], changing the mechanical structure of the antenna, and loading the switch for electrical adjustments [6; 7; 8]. Among them, the loading switch is simple and flexible and can make the antenna structure relatively compact. The commonly applied switches are PIN diodes, varactor diodes, MEMS switches, etc. [9; 10; 11]. For example, in 2007, [PERSON] introduced a dual-band reconfigurable gap dipole antenna array controlled by an MEMS switch, capable of achieving peak gains of 7.4 dBi and 11.1 dBi at 10 GHz and 16 GHz, respectively [12]. In 2013, a U-shaped slotted antenna using three RF MEMS switches was proposed to achieve the reconfigurable characteristics of the antenna [13]. In 2018, a frequency reconfigurable antenna based on an MEMS switch designed by the North University of China could work in four different frequency states, covering 14 GHz to 22 GHz [14]. In 2020, [PERSON] et al. proposed a novel two-element multiple input multiple outputs (MIMO) reconfigurable antenna that can be switched among 600 MHz, 1.8, 2.4, 3.5, and 5.5 GHz bands [15].