| 摘要 |
Two variable frequency, fixed bandwidth bandpass 10, 410 are cascaded to form a bandpass filter with variable center frequency and variable bandpass. Each filter 10, 410 includes first (16, 416) and second (24, 424) mixers separated by a fixed bandpass filter (20, 420). Each mixer includes a control input terminal 30, 32: 430, 432 which receives a control signal (fLO, fOFF). The center frequency of the filter arrangement is controlled by the frequency of control signal fLO, and the bandwidth is controlled by the difference frequency between fLO and fOFF. A tracking arrangement 456 allows direct control of the bandpass by control of the frequency of an offset oscillator 458.
|
