Tunable Couplers: An Overview of Recently Developed Couplers With Tunable Functions

With the continued development of communication technology, communication systems are required to support ever more operational frequencies and standards, which has resulted in increased complexity, cost, and size of RF front ends. Thus, miniaturized and integrated microwave devices are in high demand. In addition, frequency hopping, which helps overcome the limitations of poor anti-interference and weak security of fixed-frequency communication systems, requires the transceivers to switch to different operating frequencies and modes according to the spectrum environment. At the same time, multifunctional reconfigurable systems can free up scarce spectrum resources by switching to different operational modes depending on the spectrum environment. To leverage these advantages and to meet the aforementioned challenges and requirements of applications, it is important, both from a theoretical and an engineering standpoint, to study the integrated design of multifunctional reconfigurable microwave devices.