| 摘要 |
A re-entrant resonant cavity (12) includes a first metallized molded plastic component (18), which comprises a re-entrant stub (17), an end wall (14) and a cylindrical side wall (13). The component (18) is surface mount soldered to a metallized PCB substrate (19). A rostrum (24) is located facing the end face (21) of the stub (17) to define a capacitive gap (22) with it. The end face (21) of the stub (17) and the rostrum (24) are configured such that relative rotation between them changes the profile of the gap (22) and hence the gap capacitance. By suitably locating the two parts during manufacture, a particular capacitance may be chosen to give a desired resonance frequency from a selection available depending on the relative angular position of the stub (17) and rostrum (24). In another cavity, the rostrum is replaced by an etched metallization layer of a printed circuit board. |
