A very thin waveguide filter with attenuation poles constructed by impedance-step slot-loaded patches

A waveguide filter loading frequency selective surface (FSS) is very useful, because it make attenuation poles without using any additional couplings and structures. This kinds of the conventional filters must take the interval of a quarter-wavelength between the adjacent FSSs. So, we first exhibit that a very thin filter can be constructed by the FSSs with the “U”-shaped slot-loaded patch. However, in this filter, there is an unnecessary resonance in the low frequency region. So, we propose a new shape loading a impedance-step. Finally, the proposed filter has been fabricated, and its effectiveness is verified experimentally.