Accurate evaluation of capacitive current characteristics in multi-circuit distribution cables laid in a common trench is vital for ensuring operational reliability, suppressing induced sheath voltages, and minimizing mutual coupling effects. Traditional time-domain methods often fail to capture high-frequency oscillations, modal switching, and environmental interactions, limiting their predictive accuracy. To address these challenges, this research develops a frequency-domain analysis framework based on the Discrete-Time Fourier Series (DTFS), enabling precise assessment of capacitive current dynamics and induced sheath voltages with reduced computational burden. The methodology integrates cable geometry, conductor spacing, insulation properties, soil permittivity, and trench configuration into a unified frequency-domain model, further validated against Frequency-Dependent Line Models (FDLINE) and the Universal Line Model (ULM). Simulation and experimental results demonstrate that optimized trench arrangements significantly improve electromagnetic performance. Compared with single-line configurations, balanced layouts achieved a 38% reduction in sheath voltage (248 V ? 154 V), a 70% reduction in capacitive current imbalance (26.4% ? 7.9%), a 58% reduction in total harmonic distortion (12.5% ? 5.3%), and 44% higher attenuation at 1.2 kHz (?12.7 dB ? ?18.4 dB). Energy dissipation factors decreased by 21%, while phase displacement improved by 64%, confirming enhanced dielectric efficiency and reactive synchronization. Comparative model evaluation revealed that DTFS provided close alignment with FDLINE and ULM predictions, achieving a validation ratio of 96.8%, while maintaining superior computational efficiency over Non-Linear Transformation (NLT) techniques. The proposed framework offers a robust and practical tool for design validation, fault prediction, and environmental impact assessment in common trench installations, ensuring optimized cable performance and long-term operational reliability.