This paper presents a novel frequency selective window for waveguide filters. It has a resonant characteristic with two attenuation poles on both sides of a passband, that is, a dual-behavior resonance. Such frequency selective windows make it possible to construct a compact bandpass filter having multiple attenuation poles without any additional coupling structures. As design examples, we show 3-pole Chebyshev waveguide filters with six attenuation poles in both the microwave and the millimeter-wave regions. The validity of the present filters is proven by the comparison of the frequency characteristics between the calculated and the measured results.
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