For an efficient and reliable transmission of data beyond 5G and 6G technologies, proper waveguide structures are needed. We present a rectangular solid-core slotted cladding photonic crystal fiber (PCF) and analyze its signal transmission capability in the terahertz (THz) regime. The proposed PCF performances have been investigated numerically using the finite element method. Various parameters, such as birefringence, core power fraction, effective material loss, effective area, mode-field diameter, beat length, dispersion, confinement loss, etc., have been studied by varying the geometry of the PCFs. The obtained simulation results exhibit dispersion of the order 2 ns / THz / cm, high birefringence of 0.0983, low confinement loss of the order 10 ^{− 19} mm ^{− 1}, the effective area of 0.073 mm², and high core power fraction of 99.8% in 0.2 to 2 THz range. All the parameters have been optimized among six different structures of the proposed PCF. This analysis will be helpful for the researchers to predict the transmission capability of THz waves in a rectangular PCF waveguide, which assures the boost in communication beyond 5G toward 6G evolution.