| 摘要 |
17 The invention discloses a three-port filter being able to connect alternately a receiver and a transmitter to a common antenna in a radio system operating by the time division principle. The first signal path between the first and the third ports comprises all resonators (R1, R2, R3, R4) The second port is connected to one (e.g. R3) of the resonators in the first signal path, whereby a first subset (R1, R2) of resonators lies between the first and the second ports, and a second subset (R3, R4) of resonators forming the signal path between the second and the third ports lies between the second and the third ports. The resonators of either subset are switchable resonators, whose resonance frequencies can be shifted between two frequencies by an external control (Control). At the first control value of the control (Control) the resonators of this subset pass the RF-signal substantially without attenuation, and at the second control value they strongly attenuate said signal.
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