A new compact microstrip stacked-SIR bandpass filter with transmission zeros

This paper presents a new class of bandpass filters based on a stacked-SIR (stepped Impedance resonators) configuration. By stacking multi-coupled SIR's, the longitudinal dimension of the resulting filter is not Increased despite the increase of the filter order, so that the area of the whole filter is very compact. The use of SIR's assures that the filters have a wide upper stopband. In addition, with proper tapped input and output couplings, this new bandpass filter structure is capable of generating at least two transmission zeros. Of filters of orders 2 and 4, simulated responses show three transmission zeros in the stopband. Two third-order filters with transmission zeros purposely located at twice the center passband frequency (2f₀) are fabricated and measured to demonstrate the design.