Design of a New Low-Pass Filter in the Hairpin Structure with a Chip-Capacitor

A compact and wide stopband low-pass filter (LPF) which consists of a hairpin structural resonator, a chip-capacitor, and inductor lines is proposed in this paper. With the capacitor loaded, the hairpin structure realized three transmission zeros in the stopband. The LPF with one hairpin unit was designed using the conventional prototype design procedure in the passband. To further improve the stopband characteristics, the LPF with three hairpin units was studied and designed with the same manner as in a one unit LPF. The finally designed three-hairpin LPF showed mostly 60dB rejection characteristics in the conjunction with defected ground condition for avoiding the spurious response at the stopband. The measurement results agreed well with simulated ones.