A group-delay-compensation admittance inverter for full-passband self-equalization of linear-phase band-pass filter

Abstract

A group-delay-compensation (GDC) admittance inverter (J-inverter) is proposed for the full-passband self-equalization of the linear phase band-pass filter (BPF). The proposed GDC J-inverter consists of a coupled-line section, two resistors, and two short-circuited lines. Its group delay (GD) has two local minima located symmetrically at both sides of the center frequency, which can be used to effectively reduce the GD fluctuation at the edge of the passband for realizing the full-passband self-equalized linear-phase BPF. The positions and magnitudes of the GD local minima are controllable by adjusting the characteristic parameters of the coupled lines and the short-circuited lines and the values of the resistors. To verify the design concept, a 3-order BPF based on the proposed GDC J-inverter is designed and compared with the BPF based on the traditional J-inverter. From the measured results, the GD fluctuation of the proposed BPF within the bandwidth of |S21| > −3 dB and the bandwidth of |S11| < −10 dB are 0.23 and 0.21 ns, respectively, which improves by 50% compared with that of the BPF based on the traditional J-inverter. Meanwhile, the out-band selectivity of the proposed BPF is almost the same as that of the BPF with the traditional J-inverter.