Compact SIW BPF Loaded with a Tree Shaped Fractal Slot for LEO Satellite Communication Systems

This article presents a miniaturized substrate-integrated waveguide (SIW) bandpass filter (BPF) based on fractal geometry. The proposed filter miniaturization is achieved by etching a slot on the top layer of the structure using a tree-slotted fractal technique. The BPF covers a frequency range from 11.49 GHz to 12.24 GHz, with a fractional bandwidth (FBW) of 6.42% centered at 11.87 GHz. The miniaturized filter demonstrates improved scattering parameter characteristics with a high rejection band in both the lower and upper-frequency regions, resulting in a more compact SIW cavity. The passband poles of the filter are located at 11.78 GHz and 11.92 GHz, with reflection coefficient (S11) values of −37 dB and −30.4 dB, respectively. The insertion loss (IL) is measured to be 1.1 dB with return loss (RL) better than 27.5 dB with a group delay of about 1.6989 ns. The unloaded SIW BPF is still bulky compared to the microstrip BPF. To miniaturize it, a second iteration of tree-shaped fractal slots has been etched into the top layer of the proposed structure. The presented filter occupies an area of 17.8×8.6 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (1.17×0.56 λg<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>). Rogers RO4003c substrate was used to build the proposed filter. The substrate has a relative permittivity of 3.55 with a loss tangent of 0.0027 and a thickness of 0.508 mm. Finally, a simulation of the compact single-layered second-order Chebyshev SIW-based BPF design was implemented, and results were verified in two widely used full-wave simulators, Ansys EDT and CST.