| 摘要 |
<p>A filter for a telecommunication system, designed to suppress a signal frequency Fa and to transmit an adjoining frequency Fb without significant attenuation, comprises a resonant cavity of prismatic shape longitudinally traversed by a conductive coil wound on a hollow dielectric core into which an adjusting screw is inserted. One end of the coil is grounded at the cavity wall while its other end is left unconnected and forms with the adjusting screw a variable capacitance Cd with distributed constants; a lumped-constant tuning capacitor C1 is connected between ground and an input lead connected to an intermediate tap on the coil, the inductance L2'' of that lead and the inductance L2' of the coil portion between the tap and ground forming an inductive voltage divider bridged by the lumped-constant capacitor C1. The remainder of the coil, lying between the tap and the unconnected end, forms an inductance L1 which together with the distributed-constant capacitance Cd shunts the portion L2' of the inductive divider and forms a series-resonant circuit tuned to frequency Fa; the combination of voltage divider L2', L2'' and lumped-constant capacitor C1 constitutes a parallel-resonant circuit tuned to frequency Fb.</p> |
