Channel Capacity Analysis of Mid-Range Multigigabit Transmission Over Dielectric Waveguides

Dielectric waveguides (DWGs) have drawn great attention in millimeter-wave high-speed communication. Loss and dispersion of DWGs have been the limiting factors for utilizing the large bandwidth in the subterahertz band. Previous works have explored the restriction of maximal data rate by dispersion. However, there remains a need for more comprehensive mathematical and electromagnetic theory derivations, as well as experimental validation. In this article, a series of hollow circular PTFE fibers are simulated and measured for their s-parameters, confining a range of diameters. A baseband equivalent frequency response of DWG is proposed to remove the upconversion and downconversion from the analysis of signal transmission. Eye diagrams prove that the frequency notch below the Nyquist frequency rather than pulse broadening is the main mechanism that limits the data rate for coherent demodulation. Based on that, a negative exponential dependence and an inversed square root dependence of channel capacity on fiber length are derived for signal-to-noise ratio (SNR) and dispersion limitation. It is revealed that the channel capacity is sequentially limited by bandwidth, dispersion, and SNR as the link distance increases. Guidance is given on fiber selection. For short-to-medium range with sufficient power budgets, fibers should be optimized for minimal dispersion; to achieve long link distance or power-efficient transceiver design, fibers with small sectional area are preferred to acquire low loss and elevate the SNR limitation.