Broadband bandpass filter with multiple spurious suppression for microwave-based head imaging

Broadband bandpass filter with compact size, wide stopband and sharp upper cut-off band is presented. The filter is designed to cover the band that can be used in microwave-based head imaging for stroke detection. The proposed filter uses a low impedance feeding network, a pair of folded parallel coupled microstrip line, a rectangular microstrip resonator, and cross coupled open-ended stubs. A prototype is designed with bandwidth 1.9 GHz (centered at 2.45 GHz) and more than 15 dB attenuation at the stopband that extends up to 20 GHz. The rate of the upper cutoff frequency is more than 140 dB/GHz.