1. Introduction
Recently, there has been a lot of focus on wearable antenna technology, which has many potential applications. Generally, these applications involve the use of body-area networks (BANs), which include on-body, off-body, and in-body communications, and enable signals to be transmitted from sensors located at different positions on (or in) the human body. The information collected by these sensors may include parameters pertaining to the wearer's health, such as blood-glucose levels and heart rates [1]–[3], or external parameters such as temperature and humidity to enable certain assessments to be made about the safety of the surroundings. Antennas may also be embedded within ingestible capsules that enable us to determine the conditions of internal organs [4]. In this case, the data acquired by the sensors would be transmitted from inside the body to a device on the body, where it may be stored until it is downloaded manually or forwarded wirelessly to a central location such as a nurses' station in a hospital. Wearable antennas are also deemed useful in applications where persons are based in remote locations, e.g., in military and farming applications, where assistance may be some distance away [5]. In such cases, it would be useful for the person receiving the signals to be able to monitor the wearer's vital signs to enable remote assistance to be rendered based on real-time information about the user's condition.