Microstrip linear filter, duplexer and radio-frequency device

The invention discloses a microstrip line filter, which comprises a chamber which is provided with a PCB plate; the top and bottom inner wall of the PCB plate and the chamber are provided with a certain air height; the two sides of the PCB plate are both provided with corresponding cross cascaded transmission line and the cross cascaded transmission line arranged on one side of the PCB plate is connected with the transmission line on the other side through a hole. The invention also discloses a corresponding duplexer and a radio-frequency device. The embodiment of the invention has the advantages of simple producing processing, high quality rate, low transmission loss, low cost, etc.