| 摘要 |
PURPOSE:To reduce insertion loss by providing two sets of band stop filter where plural series resonance circuits are connected by a coaxial cable, and selecting the length of the coaxial cable longer for one and shorter for the other to a 1/4 wavelength of the blocking frequency. CONSTITUTION:Center frequencies of each band of transmission/reception in an antenna common use unit are taken respectively as fT0, fR0 and the relation of, e.g., fT0<fR0 is established. A band stop filter connected to a transmission terminal Tx 41 consists of a series resonator 44 and a coaxial cable 46, the resonator 44 is tuned to the frequency fR0, the cable 46 is designed to be short in length by 5-20% of 1/4 of the wavelength lambdaR of the fR0 and the length of the coupling cable 48 connected to an antenna terminal 43 is selected as lambdaR/4. The series resonator 45 at the reception terminal Rx 42 is turned to the frequency fT0, the length of the coaxial cable 47 is designed longer by 5-20% of 1/4 of the wavelength lambdaT of the fT0 and the length of the coupling cable 49 is selected as lambdaT/4. Thus, the frequency fR0 is not propagated to the terminal 41 from the terminal 43 and the frequency fT0 is not propagated to the terminal 42, the frequency characteristic is asymmetric to the center frequency of the band and the insertion loss of the pass band is reduced. |
