Abstract: A simple dual-band band-pass filter is proposed. It is composed of an unequal-length cross-shaped resonator and parallel coupled lines feed structures. Due to the symmetry of the filter distribution circuit, the transmission zero and transmission pole are analyzed using the even-odd mode analysis method. The designed filter has 3 transmission zeros and 4 transmission poles. The positions of the transmission zeros do not change with the changing of the impedance parameters. Among 4 transmission poles, the first even-mode transmission pole and the first odd-mode transmission pole constitute the first passband, and the remaining two transmission poles constitute the second passband. Compared with the equal-length cross-shaped filter, this structure has one extra transmission pole. The passband bandwidth can be adjusted by adjusting the position of the transmission poles. Then the physical parameters of the designed filter are given. The simulated results of the designed filter are obtained. Finally, the designed filter is fabricated and measured. Simulations are basically consistent with the measured ones, which verify the correctness of the design theory.

Key words: unequal length cross-shaped resonator, dual-band band-pass filter, transmission pole, transmission zero