A Compact Thermal Model and a New Cooling Factor Metric for Active Antennas

Abstract

This article introduces a compact thermal model (CTM) for antenna-level analysis of the printed circuit board (PCB) structures that enables fast and accurate prediction of the chip temperature (T
_chip) under varying structural and environmental conditions. The CTM represents conduction within the antenna system and convection and radiation to the environment through an equivalent lumped-element network, providing a computationally efficient alternative to full thermal simulations. A principal contribution is the definition of the antenna cooling factor (ACF), a new parameter that quantifies cooling capability of the antenna and its influence on the resulting T
_chip. The ACF offers designers a direct means to assess thermal behavior during the antenna design process, thereby supporting integrated electrothermal codesign of antenna systems. Using the proposed model, designers can simultaneously assess electromagnetic (EM) characteristics (e.g., bandwidth (BW) and maximum realized gain), structural thermal constraints (e.g., chip or antenna temperature), and joint parameters such as antenna noise temperature. The proposed CTM and ACF framework is validated experimentally using a dedicated thermal measurement setup. Nine antenna prototypes resonating at 3.5 GHz with different dielectric materials, element sizes, and antenna types are fabricated, connectorized, and characterized through combined EM and thermal measurements. The strong agreement between measurements and model predictions confirms the accuracy and practical relevance of the approach. The results establish a systematic methodology for incorporating thermal performance into antenna design with minimal computational load.