Toward Hyper-Compact Rotman Lenses: Meta-Transmission Line Design and Characterization

We present the design and characterization of a linear meta-transmission line (meta-TL) suitable for realizing hyper-compact Rotman lenses. Rotman lenses are true time delay beamforming networks that usually find applications in very-/ultra-high frequency systems such as satellite, radar, and unmanned aerial vehicle systems. The lenses designed using existing techniques tend to be at least $\mathbf{5}-\mathbf{6}\boldsymbol{\lambda}$ long making them infeasible for practical implementations. In this work, we propose a topology that achieves a very high degree of miniaturization by modifying the lumped element transmission line model. Specifically, by introducing mutual inductance terms between the first nearest neighbors in the lumped element model, we realize the meta-TL. The meta-TL can extend the linearity of the dispersion diagram by slowing down the wave within the line and lead to miniaturization. A 1D meta-TL has been designed, fabricated, and characterized demonstrating good transmission performance up to the cut-off frequency.