Instead of asymmetric molecular substitution, we investigate the molecular rectification originating from asymmetrical electrode−molecule contacts using density functional theory combined with the nonequilibrium Green’s function method. In the porphyrin-based molecular junction, we employ an additional thiol group on the left side to enhance the electronic coupling. The transportation of these contact-asymmetrical junctions shows obvious rectification, implying that the asymmetrical interface modification is feasible in the design of molecular diodes. The theoretical calculations show that the rectification ratio is about 2.6 in the large bias range from 0.6 to 1.2 V. We give an interpretation using the alignment of the molecular orbital levels to the biased electrodes in the metal−molecule−metal junction. This highlights the fact that contact asymmetry is a significant factor to be considered when evaluating nanoelectrical junctions incorporating single molecules.

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A full-passband linear-phase band-pass filter (BPF) equalized with negative group delay circuits (NGDC) is proposed. The NGDCs are utilized to suppress the salient group delay at the edge of the passband of the traditional BPF for achieving the full-passband linear-phase characteristic. To obtain input-and output-port impedance matching, two BPFs loading NGDCs are center symmetrically configured by Wilkinson power dividers. To verify the design concept, a 3-order full-passband linear-phase BPF is designed and fabricated. From the measured results, the GD fluctuation is reduced by 74% from 0.57 to 0.15 ns, return loss is better than 10 dB, and the insertion loss variation is less than 3 dB within the frequency range from 2.142 to 2.804 GHz. The proposed BPF achieves a flat group delay in the whole passband and realizes the full-passband linear-phase characteristic. INDEX TERMS Band-pass filter, full-passband linear phase, group delay equalization, negative group delay circuits.