Design of a compact dual-band dual-mode microstrip filter with an adjustable transmission zero

A novel compact microstrip dual-band filter with an adjustable transmission zero is proposed in this paper. The filter mainly consists of a microstrip stub-loaded dual-mode resonator and a half-wavelength resonator, and both are folded to make a compact configuration. The center frequencies of the two passbands are determined by appropriately choosing the impedance ratio of the stub-loaded dual-mode resonator. Through adding the half-wavelength resonator, another resonance is produced to form a two-order filtering property in the second passband. The dual-bandwidths can be controlled independently. Three transmission zeros are obtained between the two passbands, and one of them is readily adjustable by changing the length of a microstrip tuning line.