Miniaturized quad-band bandstop filter with controllable frequencies using multiple-mode resonator

The operating mechanism of the quad-band band stop filter (QB-BSF) with multiple-mode resonator (MMR) is introduced in this paper. Based on the design procedure, the operating stopband frequency locations of the proposed QB-BSF can be conveniently controlled. Also, the BSF features compact size and sharp roll-off skirts for transition bands. As an example, a QB-BSF centered at 1.23/1.8/2.4/3.5GHz with respective rejection levels of 22.5/47/52.1/23.7 dB has been designed.