Double Notch Filter for GSM-R Applications with Wide Upper Passband

In this work we present the design of a double notch (stopband) filter for GSM-R applications. The main feature of the proposed design is the very wide passband presented above the second notch (from 935 MHz to 3800 MHz). To obtain this result, a novel solution has been devised for the coupled rejection resonators realizing the notches. The proposed solution consists of capacitive-loaded cavities suitably coupled to a stripline, which connects the input to the output of the filter. The selected coupling mechanism allows the required matching up to the upper end of the passband. All the design steps are illustrated in the paper, from the synthesis of the low pass prototype to the measured fabricated device.