Miniaturized Dual-Mode Filter Using Fractal Slot and Snaky-Shape Spur-Line

In this paper, miniaturized dual-mode filters using Koch fractal slot and snaky-shape spur-line are proposed. Compared to conventional dual-mode bandpass filter (BPF), fractal slot and snaky-shape spur-line provides more current distribution distortions which improve the electrical length and realize a compact design. A size reduction of about 61.1% is obtained compared to the traditional design. In addition, the relative 3-dB bandwidth is improved by about 20.7% after adopting the second-order Koch fractal shape. This dual-mode BPF has a good prospect in compact and broad-band microstrip circuit applications.