| 摘要 |
PURPOSE:To control band-pass characteristics and trap frequency individually by connecting a microstrip line fixed at its capacity or conductivity as a trap element with a coupling part of double tuning circuits and changing the length and characteristic impedance of the microstrip line. CONSTITUTION:One end of the microstrip line 31 is opened and the length of the microstrip line 31 is set up to lambda(2n+1)/4 at the wavelength lambda of frequency to be trapped. Since the microstrip line 31 is resonated at the frequency, equivalent state with the insertion of a trap circuit is observed from a connection point between capacitors 30, 32. If the trap frequency is set up to a higher value than a transmission frequency band, the microstrip line 31 becomes equivalently capacitive because the wavelength is smaller than lambda(2n+1)/4 at the transmission frequency. Since the microstrip line 31 is opened, another distributed capacity is held between the microstrip line 31 and an earthed conductor on the back of a base plate. Thus, the characteristic impedance is changed and the coupling degree between two tuning circuits 24, 25 can be changed by changing the width of the microstrip line 31. |
