Compact bandpass filter with sharp cut-off using grooved parallel coupled microstrip lines

Abstract

A compact novel bandpass filter with sharp cut-off frequency and two transmission zeros is proposed. To be compact in size, the proposed filter is constructed using L-shaped grooved parallel coupled microstrip line (PCML) with appropriate middle resonator and short circuited via. The via is introduced to initiate a sharp lower cut-off frequency with a transmission zero at a specific frequency. The design is further improved by placing a groove at the center of the PCML structure. The groove creates sharp upper cut-off frequency with a transmission zero at specific frequencies. The filter designed at the center frequencies 2.4 GHz with bandwidths of around 400 MHz and sharp cutoff bands with 50% reduction in overall size compared with the traditional design approach.