射頻開關(guān)簡(jiǎn)化多天線系統(tǒng)

　　包含多個(gè)無線電和多個(gè)天線的手機(jī)和其他無線系統(tǒng)常常共用一些天線以減少系統(tǒng)雜波。最新的射頻開關(guān)給設(shè)計(jì)者提供了靈活性，他們需要將系統(tǒng)中的天線數(shù)目減至最小，而今天的系統(tǒng)通常可以包括一個(gè)或多個(gè)蜂窩網(wǎng)絡(luò)收音機(jī)、GPS定位無線電、wi-fi接口、藍(lán)牙無線電、調(diào)頻收音機(jī)以及其他無線電系統(tǒng)。射頻開關(guān)允許功率放大器輸出選擇系統(tǒng)所需頻帶的最佳天線，加上開關(guān)可防止兩個(gè)無線電同時(shí)從同一天線發(fā)射。

　　射頻開關(guān)可以在各種技術(shù)–機(jī)械結(jié)構(gòu)如微型繼電器和微型機(jī)電系統(tǒng)（MEMS）實(shí)現(xiàn)開關(guān)，砷化鎵（GaAs）或CMOS FET開關(guān)，甚至PIN二極管可以用在開關(guān)裝置。射頻開關(guān)的一些關(guān)鍵技術(shù)指標(biāo)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(guān)速度。機(jī)械開關(guān)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(jī)械的，它們也具有最慢的開關(guān)速度，對(duì)振動(dòng)敏感，并可能因機(jī)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.