Coupling Suppression in Compact Microstrip Lines Using Sinusoidal Geometric Modulation

Effective suppression of cross coupling in densely integrated transmission lines is crucial in compact electromagnetic systems. Conventional approaches often entail increased structural complexity or reduced fabrication compatibility. In this work, a geometrically driven coupling suppression technique is proposed based on sinusoidal modulation of the transmission line trajectory. This spatial modulation induces a spatially varying complex coupling coefficient, enabling complete destructive interference over one modulation period. Theoretical analysis reveals that the net coupling coefficient follows a zeroth-order Bessel function with respect to the modulation amplitude, allowing precise nulling at designed conditions. Full-wave simulations demonstrate over 30 dB of coupling suppression at the null frequency in a tightly spaced microstrip line pair, along with significantly reduced coupling across the operating band, while maintaining minimal degradation in input matching and near-end crosstalk. Experimental validations on three-line configurations confirm simultaneous suppression of both nearest-neighbor and next-nearest-neighbor coupling, along with efficient recovery of energy into the intended transmission path, in excellent agreement with simulation results.