Millimeter-wave and terahertz communications face a fundamental challenge: overcoming severe path loss without sacrificing spectral efficiency. Pinching antenna systems (PASS) address this by bringing radiators physically close to users, yet existing frameworks treat the waveguide as a mere transmission line, overlooking its inherent multi-mode capabilities and the critical role of polarization. This paper develops the first polarization-aware, full-wave electromagnetic model for multi-mode PASS (MMPASS), capturing spatial radiation patterns, modal polarization states, and polarization matching efficiency from first principles. Leveraging this physically grounded model, we reveal fundamental trade-offs among waveguide attenuation, atmospheric absorption, and geometric spreading, yielding closed-form solutions for optimal PA placement and orientation in single-user scenarios. Extending to multi-user settings, we propose a modular optimization framework that integrates fractional programming with closed-form polarization updates, scaling gracefully to arbitrary numbers of waveguides, PAs, and users. Numerical results show that MMPASS achieves up to a 167% increase in spectral efficiency compared with single-mode PASS. Moreover, when comparing MMPASS with its polarization-ignorant counterpart, polarization awareness alone improves the sum rate by up to 23%. By bridging rigorous electromagnetic theory with scalable optimization, MMPASS establishes a physically complete and practically viable foundation for future high-frequency wireless networks.

翻译：毫米波和太赫兹通信面临一个根本性挑战：在不牺牲频谱效率的前提下克服严重的路径损耗。捏合天线系统通过将辐射器物理上靠近用户来解决这一问题，然而现有框架仅将波导视为简单的传输线，忽略了其固有的多模态能力以及极化的关键作用。本文提出了首个考虑极化的多模态捏合天线系统全波电磁模型，从第一性原理出发捕捉空间辐射模式、模态极化态和极化匹配效率。基于这一物理驱动模型，我们揭示了波导衰减、大气吸收与几何扩展之间的基本权衡，并给出了单用户场景下最优捏合天线位置和朝向的闭式解。针对多用户场景，我们提出了一种模块化优化框架，将分数规划与闭式极化更新相结合，可灵活扩展到任意数量的波导、捏合天线和用户。数值结果表明，与单模态捏合天线系统相比，多模态捏合天线系统的频谱效率最高提升167%。此外，当将多模态捏合天线系统与其忽略极化的对应方案进行比较时，仅极化感知一项便使总和速率提升高达23%。通过将严格的电磁理论与可扩展优化相结合，多模态捏合天线系统为未来高频无线网络奠定了物理完备且实际可行的基础。