Microwave lowpass filter with improved out-of-band performance based on tilted rectangular slots

A compact microwave lowpass filter with sharp selectivity and wide stopband based on tilted rectangular slots is proposed in this paper. The developed prototype filter is based on the log periodic theory, where tilted log-periodic rectangular slots are studied for the first time. Effects resulting from the tilted slots on the performance of the studied filter are discussed and conclusions are drawn. A prototype of the proposed lowpass filter was fabricated and measured. The measured results show that the lowpass filter features a high selectivity and a wide suppression band from 4.05 GHz to 24.91 GHz under a level of 19.2 dB. Both measured and simulated performances are presented with good consistency.