Compact fractal-based bandpass filter with high selectivity for terahertz applications

A compact fractal-based microstrip bandpass filter (BPF) in dual-mode configuration loaded with X-cross slots on a square patch resonator for terahertz (THz) applications is presented in this paper. In the dual-mode frequency response of the proposed THz filter, two transmission zeros (TZs) are obtained by embedding a small square perturbation at the diagonal end of the patch resonator. Better selectivity at the edges of the filter passband is realized with such TZs. Besides, a miniaturized BPF is obtained by placing X-cross fractal slots on the patch resonator. Using different parameter sweeps like optimizing the gap size, perturbation and port widths, the selectivity of the filter and its insertion loss values are improved. The filter provides an insertion loss of 1.62 dB and return loss better than 10.8 dB at 2.95 THz desirable in sub-millimeter radiation applications. Also, the left and right TZs are observed at 2.26 THz and 3.74 THz respectively. The proposed BPF is compact in size with 10 × 10 µm² and displays a desirable performance compared to the reported filter works. The said design of the dual-mode BPF at 2.95 THz is suitable for non-destructive testing applications using THz frequencies.