射頻開關簡化多天線系統

　　包含多個無線電和多個天線的手機和其他無線系統常常共用一些天線以減少系統雜波。最新的射頻開關給設計者提供了靈活性，他們需要將系統中的天線數目減至最小，而今天的系統通常可以包括一個或多個蜂窩網絡收音機、GPS定位無線電、wi-fi接口、藍牙無線電、調頻收音機以及其他無線電系統。射頻開關允許功率放大器輸出選擇系統所需頻帶的最佳天線，加上開關可防止兩個無線電同時從同一天線發射。

　　射頻開關可以在各種技術–機械結構如微型繼電器和微型機電系統（MEMS）實現開關，砷化鎵（GaAs）或CMOS FET開關，甚至PIN二極管可以用在開關裝置。射頻開關的一些關鍵技術指標包括：通電頻率、電壓駐波比、隔離度、插入損耗、回波損耗、功率處理和開關速度。機械開關傾向于處理最高功率，并提供最低插入損耗和最佳隔離，但由于它們是機械的，它們也具有最慢的開關速度，對振動敏感，并可能因機械磨損而失敗。

　　A coaxial relay， for example， can handle high frequencies with minimal insertion losses and high power levels. A PIN diode switch is faster and has infinite life， but can only handle relatively low power and has a higher insertion loss than the mechanical switches. Lastly， FET-based switches have even higher insertion losses but lower video leakage， but are easier to integrate and can handle higher frequencies. FET and PIN diode switches are also more sensitive to overvoltages caused either by electrostatic discharge （ESD） events or by the signal itself. Coaxial relays are sensitive to vibration but relatively unaffected by ESD. Other factors to consider when selecting the best switch for an application include video leakage， ESD immunity， vibration/overstress， size， and repeatability. One issue common to all the switches is the careful circuit board layout required to minimize interference and crosstalk issues. Careful design and proper ground planes are a must to optimize isolation and minimize insertion losses.