BPFs with parametrically compensated passband insertion loss and selectivity

A new technique is proposed to improve the passband selectivity (equivalently, the compensation bandwidth) for loss-compensated bandpass filters (BPFs) that make use of the negative-resistance parametric amplification effect. The key principle of this technique is to control the resonator-to-resonator coupling properly at two selected frequencies. Theoretically, the passband response of a lossy filter can be recovered to that of the lossless case. A prototype third-order filter with a fractional bandwidth of 8% has been designed and implemented to demonstrate the idea.