Multiband bandpass filters with suppressed harmonics using a novel defected ground structure

Abstract

A novel defected ground structure, with a predominantly magnetic coupling, is designed, fabricated, and used to suppress the out‐of‐band harmonics of a class of multiband filter, characterized by very abrupt spurious response. A one‐pole lowpass filter is realized solely by making slots on the ground plane and keeping the original filter structure unchanged. The proposed structure has very minor effect on the performance of the original multiband filter, for example, on fractional bandwidths or level of S11. Measurements show the achieved suppression level of the filter spurious response to vary from 13 to 37 dB over a frequency range of about 1.5 GHz. Excellent agreements are observed between measurements and simulations within the filter bands. The filter size is maintained compact as the original. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2726–2731, 2014

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