Bandpass Frequency Selective Surface Based on Square Waveguide Structure Using 3D Printing Technology

In this paper, a novel three-dimensional (3D) bandpass frequency selective surface (FSS) is presented based on a square waveguide structure using 3D printing technology. The proposed 3D FSS is composed of a periodic array of the square waveguides with dumbbell slots embedded in waveguide walls. The square waveguide of the unit cell provides a propagation path, which can excite two resonant modes, leading to a bandpass response with one transmission pole and one transmission zero below the cutoff frequency of the square waveguide. To explain the operating principle of the proposed 3D FSS, the electric field distributions at the frequencies of transmission pole/zero are analyzed, and an equivalent circuit model is also established. For validation, a practical example is manufactured simply and rapidly, by using 3D printing technology. To verify the performance of the proposed 3D FSS, the frequency selective characteristics of the implemented 3D FSS for both TE and TM polarizations under different incident angles are measured. The measurement results show that the proposed structure exhibits dual polarizations and provides good frequency stability under incident angles from 0 degrees to 40 degrees.