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射频开关简化多天线系统
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射频开关简化多天线系统
包含多个无线电和多个天线的手机和其他无线系统常常共用一些天线以减少系统杂波。最新的射频开关给设计者提供了灵活性，他们需要将系统中的天线数目减至最小，而今天的系统通常可以包括一个或多个蜂窝网络收音机、GPS定位无线电、wi-fi接口、蓝牙无线电、调频收音机以及其他无线电系统。射频开关允许功率放大器输出选择系统所需频带的最佳天线，加上开关可防止两个无线电同时从同一天线发射。
射频开关可以在各种技术–机械结构如微型继电器和微型机电系统（MEMS）实现开关，砷化镓（GaAs）或CMOS FET开关，甚至PIN二极管可以用在开关装置。射频开关的一些关键技术指标包括：通电频率、电压驻波比、隔离度、插入损耗、回波损耗、功率处理和开关速度。机械开关倾向于处理最高功率，并提供最低插入损耗和最佳隔离，但由于它们是机械的，它们也具有最慢的开关速度，对振动敏感，并可能因机械磨损而失败。
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.
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