This paper uses the Unstructured Transmission Line Modeling Method to investigate near field interactions between a broadband microwave antenna and a platform that arise as a result of antenna installation. The antenna, feed line and the platform are represented by a common meshed model and simulated using a single time-domain numerical method. This paper aims to establish guidelines on how to achieve high accuracy when modeling both the near and far fields of an antenna whilst at the same time prioritizing computational resources. By isolating critical features such as the feed line and selected fine details of the antenna geometry the paper assesses how accurately these fine features need to be described in the model and how they affect the return loss and far field pattern of the antenna. The size of the platform, is varied from small to medium size (up to 10 wavelengths) and its impact on the antenna performance is assessed. Finally, the conclusions of the study are applied to an example of an antenna installed in the leading edge of an aircraft wing, with and without, a protective radome cover.