The random coupling model (RCM) can be used to characterize the electromagnetic coupling between multiple ports inside large complex enclosures. This statistical model combines nonrandom parameters of the enclosure and ports with a universally distributed random variable. A strong appeal of the RCM is the ability to characterize a wide variety of enclosure congurations with a limited number of parameters. However, in practical enclosures, these parameters can be difficult to obtain. In the first part of the dissertation, nonintrusive measurement methods are developed that use the time gating technique to acquire the nonrandom system parameters. Additionally, a problematic case of high loss antenna in enclosures is addressed. For the high loss antenna case, the radiation impedance is very difficult to obtain and difficult to use if obtained. For this reason, a modied random coupling model is formulated to make use of the radiation efficiency of the antennas. These methods have been successfully tested in multiple enclosures and ports. In the second part of the dissertation, the limitation of applicability of the RCM at lower frequencies is explored. The RCM assumes an overmoded cavity and that the random plane wave hypothesis applies. The breakdown of these assumptions is measured at lower frequencies and metrics are developed to determine the lowest usable frequency of the RCM. Lastly, the concepts of the RCM and the tools of microwave systems are used to experimentally validate the theory of regularization of quantum tunneling rates in chaotic cavities. The theory is based on the random plane wave hypothesis and can be studied in microwave cavities. The theory and the validating experiments are presented.