Compact tri-band bandpass filter using embedded resonators with multiple transmission zeros

A compact microstrip tri-band bandpass filter (BPF) using the embedded open stubs loaded resonator is presented. The center frequencies of the first and the third passband can be conveniently controlled by tuning the dimensions of the short stub and open stubs, whereas the second passband frequency is fixed. Moreover, the filter has been implemented with multi-transmission zeros to improve the selectivity. To verify the proposed approach, a prototype of tri-band BPF centred at 2.4/3.5/5.2 GHz for WLAN/WiMAX applications is designed and fabricated. Measured results agree well with simulated ones.