Surface acoustic wave filter

摘要

A surface acoustic wave filter includes an antenna terminal, an antenna, a transmitting filter, a variable branching line and a receiving filter. The antenna is coupled to the antenna terminal. The transmitting filter is coupled to the antenna terminal for receiving an electrical power. The variable branching line is coupled to the antenna terminal. The variable branching line has a first length when the antenna terminal is opened and has a second length that is longer than the first length when the antenna terminal is terminated so that the electrical power received by the transmitting filter when the antenna terminal is opened is smaller than it when the antenna terminal is terminated. The receiving filter is coupled to the variable branching line.