A novel coaxial-excited FSS-loaded waveguide filter with multiple transmission zeros

This paper proposes a novel coaxial-excited waveguide filter, of which the resonator is a new planar resonator called the frequency selective surface (FSS). The new FSSs located at the input and output ports are directly excited by the coaxial line. In a conventional approach, the transition from TEM mode to TE10 mode is done by the coaxial probe located at the position of a quarter guided wavelength from the backshort. In our technique, the backshort length can be chosen arbitrarily, since the transition in the proposed filter is realized by the resonance of the FSS. Additionally, the coaxial-excited FSS provides transmission zero at each stopband. Such a dual-behavior resonance of the coaxial-excited FSS makes it possible to design a very compact waveguide filter having high skirt selectivity with multiple transmission zeros. To show the effectiveness of the new filter, a design example of the three-stage bandpass filter with 4% bandwidth and six transmission zeros is presented at X band.