Future 6G communication systems call for ultrawide bandwidth in the terahertz (THz) frequency domain. Light signals propagating in photonic crystals – a functional optoelectronic material – experiences low loss in THz domain, making the material ideal for constructing devices for 6G signal processing. Adapting to such needs, we propose a novel circulator design with a NiZnFeO ferrite sphere surrounded by a triangular array of crystalline rods. The circulator achieves an operating bandwidth of 40.80 GHz at the center frequency of 0.136 THz (relative bandwidth of 31.10%) through the symmetric placement of a pair of circular aluminum plates. Sandwiching the ferrite sphere, the two plates effectively broaden the bandwidth through the external matching method yet maintain excellent isolation and insertion loss of 44.41 dB and 0.79 dB, respectively.