Planar Balanced Full-Passband Linear-Phase Dual-Port Absorptive Filter Based on Negative Group Delay Equalized Compensation

In this article, a novel planar balanced full-passband linear-phase dual-port absorptive filter is presented for the application of signal integrity in balanced systems. To absorb out-of-band reflected wave energy to prevent it from damaging the performance of neighboring active nonlinear circuits, the reflectionless characteristic of the dual-port absorptive filter is realized by loading absorptive networks at both the input and output ports. Negative group delay (NGD) equalized circuits are employed to compensate for salient group delay on both the edges of the passband achieving full-passband linear-phase characteristics. In order to solve the impedance mismatch problem caused by absorption networks and NGD equalized circuits, a quarter-wavelength impedance transformer is introduced to provide good matching characteristics. To verify the design concept, a conventional two-order balanced filter is improved into a full-passband linear-phase dual-port absorptive prototype, which is manufactured and measured with a center frequency of 2.45 GHz.