球面天线带宽与方向性的新界限：对Chu-Harrington极限的更新
New Bounds on Spherical Antenna Bandwidth and Directivity: Updates to the Chu-Harrington Limits
AI总结：
本文通过一维传输线模型重新定义球面模式Q，并用拉格朗日乘子法优化所有球谐函数激励，证明可突破Chu-Harrington极限，实现更大的天线方向性与带宽。
摘要：
Chu电路模型为分析给定球面模式的最小辐射品质因数Q提供了基础。然而，电大尺寸球面辐射体的实例清楚地表明，该Q极限在预测带宽方面存在局限性。本文重新审视了球面模式辐射，并推导出一个等效的一维传输线模型，该模型能精确模拟场分布。该模型给出了球面波导的精确截止频率，为传播场与倏逝场之间提供了清晰的界限。文中提出了一种关于“存储”与“辐射”电磁能量的新划分，从而引出了球面模式Q的新定义。接下来，关注点转向Harrington关于任意尺寸天线方向性-带宽权衡的界限。Harrington推导了在指定球谐函数数量下，使得Q不“过大”时的最大方向性。本文采用拉格朗日乘子法来量化给定带宽下的最大方向性。结果表明，最优地激励所有球谐函数（包括n>ka）能够实现比Harrington先前极限更大的方向性和带宽。虽然Chu和Harrington的分析在大多数情况下是良好的近似，但这一新的自洽理论定义了基本天线极限，得出了更新的结果。
英文摘要：
The Chu circuit model provides the basis for analyzing the minimum radiation quality factor, Q, of a given spherical mode. However, examples of electrically large spherical radiators readily demonstrate that this Q limit has limitations in predicting bandwidth. Spherical mode radiation is reexamined and an equivalent 1D transmission line model is derived that exactly models the fields. This model leads to a precise cutoff frequency of the spherical waveguide, which provides a clear boundary between propagating and evanescent fields. A new delineation of 'stored' and 'radiated' electromagnetic energy is postulated, which leads to a new definition of spherical mode Q. Next, attention is turned to the Harrington bound on the directivity-bandwidth tradeoff of an antenna with an arbitrary size. Harrington derived the maximum directivity for a specified number of spherical harmonics such that the Q is not 'large'. Here, the method of Lagrange multipliers is used to quantify the maximum directivity for a given bandwidth. It is shown that optimally exciting all spherical harmonics (including n>ka) enables both larger directivity and bandwidth than Harrington's previous limit. While Chu and Harrington's analyses are generally good approximations for most situations, the new self-consistent theory that defines fundamental antenna limits leads to updated results.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
