Traditionally, microwave filters have been implemented as passive networks of waveguide, transmission-line, or discrete lumped elements. More recently, microwave active filters have also been realized. A microwave high Q-active bandpass filter is presented. using a varactor diode for tuning, and an active component giving a substantial increase in Q of the resonant sections of filter. High-Q filter elements offer low-filter insertion loss and also yield sharp passband corners, which cannot be achieved by lossy filter and amplifier combination.
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