| 摘要 |
PROBLEM TO BE SOLVED: To obtain a common antenna system with not a large size that can prevent a sneak path of a transmission signal to a receiver side without the use of a filter with high Q. SOLUTION: An antenna of the common antenna system 1 is used in common for transmission and reception but part of a transmission signal passing through a reception band filter is added to a received signal as an intrusion signal. The antenna of the common antenna system 1 is provided with an intrusion prevention means 10 consisting of a 1st directional coupler 11 that extracts part of the transmission signal given to a transmission band filter, a delay device 12 that delays the extracted transmission signal, a phase shifter 13 that adjusts the phase of the delayed transmission signal, an attenuator 14 that adjusts the amplitude of the transmission signal whose phase is adjusted, and a 2nd directional coupler 15 that applies the attenuated transmission signal to the output of the reception band filter as an intrusion elimination signal. The intrusion elimination signal has the same delay as, the same amplitude as and the opposite phase to those of the intruded signal and cancels the intruded signal in the received signal, thus eliminating the intruded signal.
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