| 摘要 |
<p>A tunable bandstop/bandpass filter particularly suitable for use in duplex applications where the transmit and receive bands are closely located, comprises two or more reactively coupled quarter wavelength resonators (1,2) e.g. dielectric resonators. One end (3b) of each resonator is coupled to ground potential. The opposite (open-circuit) end (3a) of the resonators is coupled to adjacent resonators via coupling capacitors (14). Voltage controlled tuning means, e.g. a varactor (9,9 min ) and series connected capacitor (10,10 min ), are coupled in parallel to the open circuit end of each of the resonators respectively. The stopband/passband of the filter can thus be adjusted by varying the voltage applied to the tuning means. Additionally, in the case of a bandpass filter a tunable zero (or "notch") may be introduced into the transmission response by including varactors (15,16) coupled in series to the open-circuit end (3a) of the resonators. <IMAGE></p> |
