Wireless body area networks (WBANs), because of their widespread applications in health care and industrial development, have an important share of the recent advancements of the Internet of things (IoT). The term “wireless” is a key element of any new user-friendly wearable technological devices in health monitoring. This concept is reinforced by the utilization of wearable antennas and ultimately leads to the integration of technique and clothes; therefore the concept of smart clothing has been introduced. Wearable antennas are different because they are planar, durable, and user friendly. In this regard, the most prevalent type of antenna that has variety of forms and patterns is the microstrip antenna. Planar antennas in general need flexible and thin substrates that enable them to be mounted on textiles. Consequently, materials such as felt, polyester, and denim are excellent candidates for the development of wearable antennas. The materials are known for having less loss in comparison to conventional substrates. However, the electromagnetic properties of such regular fabrics are not well known and are none of fabric manufacturer's concern. Therefore, a very simple technique to characterize the electromagnetic properties of sample fabrics as antenna substrates for wireless body communications in this study is proposed. Because microstrip antennas are less dependent on the imaginary part of the complex dielectric constant of the substrates, the unique method presented in this paper helps researchers determine the real part of the dielectric permittivity straightforwardly and without advanced knowledge of the substrate. The method can be considered as an example of applications of antennas to characterizing electromagnetic properties of materials. The structure of the method involves square-patch antennas that are directly fed at the center of the patch. The lowest resonance mode of the patch antenna is the key parameter in the process. Step-by-step procedures and materials used in this study to develop the method are explained and discussed. The stability and accuracy of the method is evaluated using simulations and measurements.