Three-dimensional bandpass frequency selective structures

Bandpass frequency-selective surfaces are very useful in many microwave applications. A traditional bandpass frequency-selective surface, consisting of a two-dimensional (2-D) periodical array of slots/apertures, is difficult to realize high selectivity, wide out-of-band rejection, and stable response under different angles of incidence. In this paper, a new class of three-dimensional (3-D) bandpass frequency selective structures (FSSs) based on an array of shielded microstrip lines are described, which can provide a number of transmission zeros/poles at desired frequencies and then exhibit high performance. A generalized equivalent circuit is also introduced to explain the operating principle of these high-performance bandpass FSSs.