Duplexer and transceiver

A duplexer, comprising:

• a first port, a second port and a third port for external input/output;
• a first path being formed between the first port and the third port;
• a second path being formed between the second port and the third port;
• a phase shifting part provided for each path, the phase shifting parts having variable characteristics;
• a resonating part provided for each path,
• wherein at least any of said resonating parts has a ring conductor having a length equal to one wavelength at a resonant frequency or an integral multiple thereof, and a plurality of switches each of which is connected to a different part of said ring conductor at one end and to a passive circuit or ground conductor at the other end;
• and
• a controlling part that controls said switches and said phase shifting parts, wherein said controlling part selects from among said switches so that the variation of the characteristics of said phase shifting parts is reduced.