Ultra-compact evanescent mode filter using inhomogeneous semi-lumped capacitive elements

This paper presents an original solution for the design of ultra-compact evanescent mode bandpass filters with extremely wide stopband. The idea consists of using inhomogeneous capacitive loadings among the various resonators so as to desynchronize the spurious frequencies while maintaining a synchronous passband for the fundamental mode. The technique is explained by presenting the design and the experimental results of a six-resonator surface mountable L-band filter having upper stopband extending up to 18 GHz.