General formulas are proposed for thoroughly evaluating the radiation efficiency of traveling-wave antennas operating in any radiating regime. Indeed, existing theoretical models only work in the scanned-beam region, where the radiating mode is considerably above cutoff and the perturbation method applies. The analysis provided here extends the application of the perturbation method close to the cutoff condition, thus providing a correct estimation of the losses even in the case of broadside radiation. This case is particularly important for Fabry–Perot cavity leaky-wave antennas (FPC-LWAs) based on partially reflecting screens (PRSs), which are commonly designed to generate a broadside pencil beam. However, the previous works on FPC-LWAs always assume either a lossless PRS, or a lossless dielectric cover layer thus neglecting metal and dielectric losses: a hypothesis that is no longer fulfilled at high frequencies, such as millimeter-wave and submillimeter-wave frequencies. An original theoretical framework is thus developed to derive analytical formulas for a rigorous evaluation of losses when either lossy PRS or lossy dielectric cover layers are employed. Interestingly, the equivalence between a lossy PRS and a lossy dielectric cover layer is shown from a theoretical viewpoint. All the findings derived here are validated through full-wave simulations to corroborate the proposed analysis.

中文翻译：

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均匀漏波天线损耗的严格评估

提出了用于全面评估在任何辐射状态下运行的行波天线的辐射效率的通用公式。事实上，现有的理论模型仅适用于扫描光束区域，其中辐射模式远高于截止频率并且适用微扰方法。此处提供的分析扩展了接近截止条件的扰动方法的应用，从而即使在宽边辐射的情况下也能提供对损耗的正确估计。这种情况对于基于部分反射屏 (PRS) 的法布里-珀罗腔漏波天线 (FPC-LWA) 尤为重要，该天线通常设计用于生成宽边笔形波束。然而，之前关于 FPC-LWA 的工作总是假设要么是无损 PRS，要么 或无损电介质覆盖层，因此忽略了金属和电介质损耗：在高频下不再满足的假设，例如毫米波和亚毫米波频率。因此，当使用有损 PRS 或有损电介质覆盖层时，开发了一个原始的理论框架来推导出用于严格评估损耗的分析公式。有趣的是，有损 PRS 和有损电介质覆盖层之间的等效性是从理论角度显示的。这里得出的所有发现都通过全波模拟得到验证，以证实所提出的分析。因此，当使用有损 PRS 或有损电介质覆盖层时，开发了一个原始的理论框架来推导出用于严格评估损耗的分析公式。有趣的是，有损 PRS 和有损电介质覆盖层之间的等效性是从理论角度显示的。这里得出的所有发现都通过全波模拟得到验证，以证实所提出的分析。因此，当使用有损 PRS 或有损电介质覆盖层时，开发了一个原始的理论框架来推导出用于严格评估损耗的分析公式。有趣的是，有损 PRS 和有损电介质覆盖层之间的等效性是从理论角度显示的。这里得出的所有发现都通过全波模拟得到验证，以证实所提出的分析。