Broadband Bandpass Filters Using Slotted Resonators Fed by Interdigital Coupled Lines for Improving Upper Stopband Performances

This paper proposes new broadband microstrip bandpass filters based on slotted linear tapered-line resonator (SLTR) and slotted stepped impedance resonator (SSIR) structures for size reduction and improved stopband performances. A comprehensive treatment of slot resonators and both ends of the resonator with interdigital coupled lines is described. The design concept is demonstrated by two filter examples including one with a slotted linear tapered-line resonator (SLTR) and another one with a slotted stepped impedance resonator (SSIR). These filters have not only compact size but also a wider upper stopband resulting from resonator bandstop characteristics. The simulated and experimental results of stopband performances are better than 15 dB for a frequency range up to 25 GHz.